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Probiotics for the prevention of Clostridium difficile-associated diarrhea in adults and children

  1. Joshua Z Goldenberg1,
  2. Stephanie SY Ma2,
  3. Jane D Saxton1,
  4. Mark R Martzen3,
  5. Per O Vandvik4,
  6. Kristian Thorlund5,
  7. Gordon H Guyatt5,
  8. Bradley C Johnston6,7,*

Editorial Group: Cochrane Inflammatory Bowel Disease and Functional Bowel Disorders Group

Published Online: 31 MAY 2013

Assessed as up-to-date: 21 FEB 2013

DOI: 10.1002/14651858.CD006095.pub3


How to Cite

Goldenberg JZ, Ma SSY, Saxton JD, Martzen MR, Vandvik PO, Thorlund K, Guyatt GH, Johnston BC. Probiotics for the prevention of Clostridium difficile-associated diarrhea in adults and children. Cochrane Database of Systematic Reviews 2013, Issue 5. Art. No.: CD006095. DOI: 10.1002/14651858.CD006095.pub3.

Author Information

  1. 1

    Bastyr University, Seattle, WA, USA

  2. 2

    McMaster University, Division of Plastic & Reconstructive Surgery, Hamilton, Ontario, Canada

  3. 3

    Bastyr University, Bastyr University Research Institute, Kenmore, WA, USA

  4. 4

    Norwegian Knowledge Centre for the Health Services, Oslo, Norway

  5. 5

    McMaster University, Department of Clinical Epidemiology and Biostatistics, Hamilton, Ontario, Canada

  6. 6

    The Hospital for Sick Children Research Institute, Toronto, Ontario, Canada

  7. 7

    University of Toronto, Institute of Health Policy, Management and Evaluation, Toronto, Ontario, Canada

*Bradley C Johnston, bradley.johnston@sickkids.ca. bjohnst@mcmaster.ca.

Publication History

  1. Publication Status: New
  2. Published Online: 31 MAY 2013

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Characteristics of included studies [ordered by study ID]
Arvola 1999

MethodsPlacebo controlled RCT, follow-up: 3 months post first antibiotic administration


ParticipantsPediatric population, primarily outpatients (inpatients 5/119 outpatients 114/119), Finland, unclear if patients with recurrent C. difficile were included


InterventionsL. rhamnosus GG 53103, 40 x 109 cfu/day for duration of antibiotic treatment


OutcomesCDAD, AAD and AE


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Low risk“The patients were randomized by means of a computer program”

Allocation concealment (selection bias)Unclear riskNo pertinent information provided, therefore it is unclear if allocation was successfully concealed. Empirical data from an analysis of 1346 trials suggests that unclear and inadequately concealed allocation can bias trials with unpredictable magnitude. However, unclear or inadequately concealed allocation was associated with bias only with subjective outcomes. There is little evidence of such bias with objective outcomes (Wood 2008)

Blinding of participants and personnel (performance bias)
CDAD
Low risk “Lactobacillus GG and placebo capsules were indistinguishable in appearance and taste”

“All patients received the same information and the follow-up was conducted in a similar manner”

“Lactobacillus GG and placebo capsules also were indistinguishable in appearance and taste when opened”

Blinding of participants and personnel (performance bias)
AE
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of participants and personnel (performance bias)
AAD
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of outcome assessment (detection bias)
CDAD
Low riskThere was no explicit statement about blinding of ‘outcome assessors.’ The outcomes of interest in our review relevant to this study are CDAD, AE and AAD. The outcome of diarrhea was assessed by the parents of the participants. As the parents were blinded we consider this outcome to be assessed blind. In cases of diarrhea, samples were analyzed for C. difficile. There is no mention of blinding of the cytotoxin assay personnel although this is a placebo controlled drug trial so we will consider the risk of bias to be low here. Additionally, we consider the cytotoxin assay to be an ‘objective outcome’ which is less susceptible to bias based on inadequate blinding (Wood 2008)

Blinding of outcome assessment (detection bias)
AE
Low risk“The parents reported no adverse effects of Lactobacillus GG or placebo.” While not explicitly mentioned as an outcome in the ‘methods’ section AE were reported on in ‘results.’ It appears AE were assessed via report from the parents who were blinded therefore we consider this outcome to be assessed blinded as well  

Blinding of outcome assessment (detection bias)
AAD
Low riskThe outcomes of interest in our review relevant to this study are CDAD, AE and AAD. The outcome of diarrhea was assessed by the parents of the participants. As the parents were blinded we consider this outcome to be assessed blind

Incomplete outcome data (attrition bias)
CDAD
High risk29% dropout. No mention of intention-to-treat analysis. Unbalanced loss to follow-up (20 placebo, 28 active) with only two observed events of C. difficile. It seems a per protocol analysis was done. As the event rates were extremely low we consider this a high risk of attrition bias

Incomplete outcome data (attrition bias)
AE
High riskSee above: Incomplete outcome data (attrition bias) CDAD

Incomplete outcome data (attrition bias)
AAD
High riskSee above: Incomplete outcome data (attrition bias) CDAD

Selective reporting (reporting bias)Low riskNo independent protocol was identified. All outcomes declared in ‘methods’ were reported on in ‘results.’ While not listed explicitly as outcomes, viral and bacterial analyses including C. difficile assay were described in ‘methods’ and reported on in ‘results.’ In addition, while not described in ‘methods’ AE were reported on in ‘results’ as well

Other biasLow riskFunding sources listed and did not include industry sponsors. Baseline characteristics of participants included in analysis appeared roughly equal and evenly distributed. No other risk of bias identified

Beausoleil 2007

MethodsPlacebo controlled RCT, follow-up: 3 weeks after last drug dose


ParticipantsAdult population, inpatient, Canada, 2/44 patients in the treatment arm and 4/45 in the control arm had a history of C. difficile infection


InterventionsFermented milk containing L. acidophilus CL1285 and L. casei 25 x 109 cfu/day for 2 days then 50 x 109 cfu/day for duration of antibiotic course or placebo fermented milk


OutcomesCDAD,AAD, and AE


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskThe method of randomization was not adequately reported in this paper

Allocation concealment (selection bias)Unclear riskNo pertinent information provided, therefore it is unclear if allocation was successfully concealed 

Blinding of participants and personnel (performance bias)
CDAD
Low risk”Both preparations were provided in identically labelled containers; their taste and texture were similar”

Blinding of participants and personnel (performance bias)
AE
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of participants and personnel (performance bias)
AAD
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of outcome assessment (detection bias)
CDAD
Low riskNo explicit statement about blinding of ‘outcome assessors.’ The primary outcome of AAD was defined by stool frequency and consistency. It appears as if this assessment was done by the participant. Secondary outcomes include adverse events (also reported by the participant) and cytotoxin assay. The participants were blinded so those outcomes involving participant assessment are assumed to be assessed blinded. There is no mention of blinding of the cytotoxin assay personnel although this is a placebo controlled drug trial so we will consider the risk of bias to be low here. Additionally, we consider the cytotoxin assay to be an ‘objective outcome’ which is less susceptible to bias based on inadequate blinding (Wood 2008

Blinding of outcome assessment (detection bias)
AE
Low riskSee above: Blinding of outcome assessment (detection bias) CDAD 

Blinding of outcome assessment (detection bias)
AAD
Low riskSee above: Blinding of outcome assessment (detection bias) CDAD 

Incomplete outcome data (attrition bias)
CDAD
High riskThe testing of samples for C. difficile differed between groups:. 7 patients in active arm developed AAD, of these 2 were tested for C. difficile, 1 of whom was positive. In the placebo arm 16 patients developed AAD, yet 13 were tested for C. difficile and 7 were positive. It is unclear why all diarrhea samples were not tested as this was part of protocol stated in the ‘methods.’ Therefore for the outcomes involving C. diffile there is substantial incomplete outcome data that could have resulted in ‘material’ bias of results for these outcomes

Incomplete outcome data (attrition bias)
AE
Low riskThere were no patients lost to follow-up

Incomplete outcome data (attrition bias)
AAD
Low riskThere were no patients lost to follow-up

Selective reporting (reporting bias)Low riskA protocol for this study could not be identified. All outcomes discussed in ‘methods’ were reported in ‘results’

Other biasLow risk“Product and placebo were provided by Bio-K+ International Inc, Laval, Quebec. A research grant was provided by Bio K+ International Inc to cover the pharmacy administration fees.” While a producer of the active treatment was a financial sponsor no author is from the sponsoring agency

Bravo 2008

MethodsPlacebo controlled RCT, follow-up: 9 days after last study drug dose


ParticipantsMixed population (15 to 81 years of age), outpatient, Chile, unclear if patients with recurrent C. difficile were included


InterventionsS. boulardi 10.2 x 109 cfu/day for 12 days (duration of antibiotic course 5 to 10  days) or placebo


OutcomesCDAD, AAD and AE


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskThe method of randomization was not described in this paper

Allocation concealment (selection bias)Unclear riskNot enough information provided

Blinding of participants and personnel (performance bias)
CDAD
Low risk“In a controlled randomized, double blind trial...” 

Blinding of participants and personnel (performance bias)
AE
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of participants and personnel (performance bias)
AAD
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of outcome assessment (detection bias)
CDAD
Low riskThere is no explicit mention of outcome assessor blinding. There is no mention of blinding of the cytotoxin assay personnel although this is a placebo controlled drug trial so we consider the risk of bias to be low here. Additionally, we consider the cytotoxin assay to be an ‘objective outcome’ which is less susceptible to bias based on inadequate blinding (Wood 2008

Blinding of outcome assessment (detection bias)
AE
Low riskIt appears AE were assessed by participants reporting to study personal all of whom were blinded

Blinding of outcome assessment (detection bias)
AAD
Low riskSee above: Blinding of outcome assessment (detection bias) AE

Incomplete outcome data (attrition bias)
CDAD
High riskThere were four losses to follow-up reported in this paper, two from each group. Analysis was done intention-to-treat although sensitivity analysis was performed for efficacy. All 86 participants who were enrolled and not excluded from onset due to exclusion criteria were analyzed. However, not all diarrhea samples were tested for C. difficile. Three participants in the active arm developed AAD. Of these patients, 3 were tested for C. difficile, 0 of which were positive for the toxin. In the placebo arm 5 participants developed AAD yet only 1 was tested for C. difficile and 0 were positive. Because 4 other placebo AAD cases were not evaluated for C. difficile we consider this a relatively high incomplete outcome rate for this outcome. For this reason we consider the CDAD outcome to have a high risk of ‘material’ bias

Incomplete outcome data (attrition bias)
AE
Low riskThere were four losses to follow-up reported in this paper two from each group. Analysis was done intention-to-treat although sensitivity analysis was performed for efficacy. All 86 participants who were enrolled and not excluded from onset due to exclusion criteria were analyzed. We do not consider this small and balanced dropout rate to reasonably and ‘materially’ affect the AE reported event rate. For this reason we consider the outcome of AE to have a low risk of ‘material’ attrition bias

Incomplete outcome data (attrition bias)
AAD
Low riskSee above: Incomplete outcome data (attrition bias) AE

Selective reporting (reporting bias)Low riskNo protocol identified. All presumed outcomes from the ‘methods’ section were reported on in the ‘results’ section

Other biasLow risk“Funding: TUSCANY Laboratory.” Funding was disclosed. It is unclear if TUSCANY produces the investigated product. No authors were associated with the funding organisation

Can 2006

MethodsPlacebo controlled RCT, follow-up: 4 weeks after last antibiotic dose


ParticipantsAdult population, inpatient, Turkey, unclear if patients with recurrent C. difficile were included


InterventionsS. boulardi lyophilized 20 x 109 cfu/day ≤ 48 hours of antibiotic start dose (duration of study drug course not stated), additional information regarding length of probiotic treatment was unclear


OutcomesCDAD and AAD


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskThe method of randomization was not adequately described

Allocation concealment (selection bias)Unclear riskNo pertinent information provided and so it is unclear if allocation was successfully concealed

Blinding of participants and personnel (performance bias)
CDAD
Low risk“…a double-blind controlled study…”

Blinding of participants and personnel (performance bias)
AAD
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of outcome assessment (detection bias)
CDAD
Low riskNo explicit statement about blinding of ‘outcome assessors.’ The outcome of diarrhea was assessed by the participants who were blinded. There is no mention of blinding of the cytotoxin assay personnel although this is a placebo controlled drug trial so in accordance with our a priori defined RoB criteria we will consider the risk of bias to be low here

Blinding of outcome assessment (detection bias)
AAD
Low riskThe outcome of diarrhea was assessed by the participants who were blinded

Incomplete outcome data (attrition bias)
CDAD
Low riskNo missing outcome data; number randomized is clearly stated and equal to number analysed. The risk of attrition bias is considered to be low for all outcomes

Incomplete outcome data (attrition bias)
AAD
Low riskSee above: Incomplete outcome data (attrition bias) CDAD

Selective reporting (reporting bias)Unclear riskA protocol for this trial could not be identified. Outcomes were not explicitly mentioned as ‘outcomes’ in the ‘methods’ section although it seems they included AAD, C. difficile, microscopic and macroscopic stool examination, and type of antibiotic used. In the ‘results’ section all were reported with the exception of stool examination. This outcome is not particularly of interest in our review, however it is suggested that this domain be assessed at the study level not outcome level (Higgins 2011). It is also unclear how ‘material’ the bias to our review would be from this omission

Other biasLow risk“Source of support: Departmental sources.” No other source of bias identified

Cindoruk 2007

MethodsPlacebo controlled RCT, follow-up: 6 weeks after last antibiotic dose


ParticipantsAdults, not specified, Turkey, unclear if patients with recurrent C. difficile were included


InterventionsS. boulardi 500 mg twice daily for 2 weeks


OutcomesCDAD, AAD and AE


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Low risk“Randomization was done using computer-based random numbers”

Allocation concealment (selection bias)Unclear riskNot specifically discussed.

Blinding of participants and personnel (performance bias)
CDAD
Low risk"Double blind"

Blinding of participants and personnel (performance bias)
AE
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of participants and personnel (performance bias)
AAD
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of outcome assessment (detection bias)
CDAD
Low riskCDAD assessment done by C. difficile toxin so risk of bias assumed to be low 

Blinding of outcome assessment (detection bias)
AE
Low riskAE assessment filled out by participants who were blinded

Blinding of outcome assessment (detection bias)
AAD
Low riskNo mention of how diarrhea was determined or assessed. Assumed to have been assessed by subjects who were blinded

Incomplete outcome data (attrition bias)
CDAD
High riskC difficile was only measured in a subset of diarrhea patients

Incomplete outcome data (attrition bias)
AE
Unclear riskNo mention of patients lost to follow-up after treatment period. Diarrhea is listed with other AE

Incomplete outcome data (attrition bias)
AAD
Unclear riskIncomplete outcome data (attrition bias) AE

Selective reporting (reporting bias)Low riskNo mention of a clinical trial register in text. Trial not found on clinicaltrials.gov. Outcome measures discussed in methods section were AE and H pylori. These outcomes were reported in results section. There was no explicit mention of a C. difficile outcome in the methods section although it was reported on in the results section

Other biasUnclear riskBaseline differences not statistically significant. No mention of funding sources

Duman 2005

MethodsNo treatment controlled RCT, follow-up: 4 weeks after last study drug dose


Participants17 to 81 yrs of age, not specified, Turkey, unclear if patients with recurrent C. difficile were included


InterventionsS. boulardi 30 x 109 cfu/day  for 14 days (i.e. for duration of antibiotic course) or no treatment


OutcomesCDAD, AAD and AE


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskThe method of randomization was not described

Allocation concealment (selection bias)Unclear riskNo pertinent information provided so it is unclear if allocation was successfully concealed

Blinding of participants and personnel (performance bias)
CDAD
Unclear risk“This is a multicentre, prospective, open label and randomized study.” This is an open label study and therefore there was knowledge of the allocated intervention and we consider this to have a high risk of performance bias. However, the magnitude of the bias may differ depending on the outcome in question.  Additionally, there is little empirical evidence that objective outcomes are subject to bias due to lack of blinding (Wood 2008

Blinding of participants and personnel (performance bias)
AE
High risk“This is a multicentre, prospective, open label and randomized study” 

Blinding of participants and personnel (performance bias)
AAD
Unclear riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of outcome assessment (detection bias)
CDAD
Unclear riskThis is an open label study and therefore there was knowledge of the allocated intervention and we consider this to have a high risk of performance bias. Participants were not blinded and they self-reported diarrhea. Therefore these outcome assessments were definitely not blinded. There is no mention of blinding for microscopic and macroscopic investigation, nor for cytotoxin ELISA. However, we assume the assessors were not blinded as this was an open label trial. The magnitude of the bias may differ depending on the outcome in question.  Additionally, there is little empirical evidence that objective outcomes are subject to bias due to lack of blinding (Wood 2008)

Blinding of outcome assessment (detection bias)
AE
High riskThis is an open label study and therefore there was knowledge of the allocated intervention and we consider this to have a high risk of performance bias. Participants were not blinded and they self-reported adverse events. Therefore these outcome assessments were definitely not blinded

Blinding of outcome assessment (detection bias)
AAD
Unclear riskSee above: Blinding of outcome assessment (detection bias) CDAD

Incomplete outcome data (attrition bias)
CDAD
High risk“The C. difficile toxin test was tested in the stool in 16 patients with diarrhea (11 in the control group and five in the treatment group) and it was positive only in one patient in the control group.” Total diarrhea cases included 28 participants in control group and 14 in treatment group. It appears that only one third of diarrhea cases in each group were assessed for C. difficile. We are very concerned with the risk of this missing outcome data especially considering the low event rate for the C. difficile and CDAD outcomes

Incomplete outcome data (attrition bias)
AE
Low riskIt appears from the presentation of results that the analysis was done with intention-to-treat. All 389 patients randomized were analysed in their groups as randomized. Missing outcome data is balanced in numbers across intervention groups, with similar reasons for missing data across groups.

Incomplete outcome data (attrition bias)
AAD
Low riskSee above: Incomplete outcome data (attrition bias) AE

Selective reporting (reporting bias)High riskA protocol for this study was not identified. All outcomes discussed in ‘methods’ were reported in ‘results.’ However an additional outcome was reported in ‘results’ (cumulative diarrhea rate).  Therefore the primary outcome of rate of diarrhea was “reported using measurements, analysis methods or subsets of the data (e.g. subscales) that were not pre-specified.” This classifies as a high risk of bias (Higgins 2011)

Other biasUnclear riskNo mention of funding source. According to our a priori criteria for RoB assessment we will assess this as an unclear risk of bias

Gao 2010

MethodsPlacebo controlled RCT with 2 actives arms (differing dose), follow-up: 3 weeks after last study drug dose


ParticipantsAdult population, inpatients, China, unclear if patients with recurrent C. difficile were included


InterventionsProbiotic arm 1: L. acidophilus CL1285 and L. casei LBC80R 50 x 109 cfu/day

Probiotic arm 2: L. acidophilus CL1285 and L. casei LBC80R 100 x 109 cfu/day within 36 hours of antibiotic commencement until 5 days after discontinuation

Placebo


OutcomesCDAD, AAD and AE


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Low risk“The randomization sequence used in this trial was generated by a computerized random-number generator (SAS, release 9.2; SAS Institute, Cary, NC) using a permuted block design that randomized among the three study groups while stratifying for age (50 – 59 vs. 60 – 70 years) and number of days on antibiotics (3 – 8 and 9 – 14 days)”

Allocation concealment (selection bias)Low risk“Study products were delivered to the investigative site in identical containers labelled only with the lot number and a sequentially numbered patient identification code”

Blinding of participants and personnel (performance bias)
CDAD
Low risk“This study was conducted using triple-blinding procedures. First, patients were blinded to the treatment received throughout the trial. Each patient received two pills each day, which were identical in shape, size, taste, smell, and color regardless of the assigned treatment group. Second, investigators and all involved clinicians were blinded to the treatment allocation throughout the course of the study. Finally, all study coordinators, clinical monitors, and biostatisticians were blinded to treatment allocation throughout the entire clinical study and until after all analyses were completed”

Blinding of participants and personnel (performance bias)
AE
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of participants and personnel (performance bias)
AAD
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of outcome assessment (detection bias)
CDAD
Low risk“This study was conducted using triple-blinding procedures. First, patients were blinded to the treatment received throughout the trial. Each patient received two pills each day, which were identical in shape, size, taste, smell, and color regardless of the assigned treatment group. Second, investigators and all involved clinicians were blinded to the treatment allocation throughout the course of the study. Finally, all study coordinators, clinical monitors, and biostatisticians were blinded to treatment allocation throughout the entire clinical study and until after all analyses were completed”

Blinding of outcome assessment (detection bias)
AE
Low riskSee above: Blinding of outcome assessment (detection bias) CDAD

Blinding of outcome assessment (detection bias)
AAD
Low riskSee above: Blinding of outcome assessment (detection bias) CDAD

Incomplete outcome data (attrition bias)
CDAD
Low riskNo missing outcome data; number randomized is clearly stated and equal to number analysed. We consider the risk of attrition bias to be low for all outcomes

Incomplete outcome data (attrition bias)
AE
Low riskSee above: Incomplete outcome data (attrition bias) CDAD

Incomplete outcome data (attrition bias)
AAD
Low riskSee above: Incomplete outcome data (attrition bias) CDAD

Selective reporting (reporting bias)Low riskProtocol was listed with clinicaltrials.gov (NCT00958308). All primary and secondary outcomes listed in protocol were reported in the ‘results’

Other biasUnclear risk“Bio-K + International (Laval, Quebec, Canada) provided financial support for this clinical trial. Sprim Advanced Life Sciences helped with study planning, conduct, and analysis and with paper development.” Three paper authors work for Sprim which is a CRO which we assume was funded by Bio-K+ since they were the sponsor of the study. So while no sponsoring employees were authors the sponsoring agency contracted the organization that planned and analyzed the study

Hickson 2007

MethodsPlacebo controlled RCT, follow-up: 4 weeks after last antibiotic or study drug dose


ParticipantsAdult population, inpatient, England, unclear if patients with recurrent C. difficile were included


InterventionsL. casei imunitass DN-114 001 19 x 109 cfu/day and L. bulgaris 1.9 x 109 cfu/day and S. thermophilus 19 x 109 cfu/day or placebo for length of course of antibiotics and for 1 week afterwards


OutcomesCDAD, AAD and AE


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Low risk“An independent statistician generated the random allocation sequence, which was stratified for hospital, sex, and two age groups (50-69 and ≥70). The sequence was given to the pharmacy on each site.” While no explicit mechanism of randomization was mentioned we will consider the involvement of an independent statistician to have led to an adequate randomization

Allocation concealment (selection bias)Unclear risk“The sequence was given to the pharmacy on each site.”

“The pharmacies removed the commercial labels, then applied study labels to identify the patient…” There is no explicit mention of allocation concealment. It appears the randomization sequence was delivered to the pharmacy and that the pharmacy assigned bottles directly to patients. While this suggests that the allocation was concealed we cannot be certain from this description and must consider as unclear

Blinding of participants and personnel (performance bias)
CDAD
Low risk“Actimel is sold in 100 g white plastic bottles with removable labels; Yazoo is packaged similarly but in 200 ml bottles. We chose Yazoo as placebo because it looks identical in colour and consistency to Actimel... The pharmacies removed the commercial labels, then applied study labels to identify the patient, the drink’s “use by” date, and storage instructions. We could not find a placebo in an identical bottle to Actimel. Patients and researchers were blind to the study drink as they did not see the bottle the drink came in. Nursing staff dispensed the drinks and were instructed to pour 100 ml into a cup for the patient; they were not told which bottle contained which drink. Older people in the UK are not generally familiar with these products, but it is possible some patients might have recognized the taste. However, we had excluded people who regularly took this or other probiotic products from the study. Potential bias through unblinding was possible but unlikely.”

 

While there is potential for unblinding here the risk of ‘material’ bias is unclear and would depend on how many participants could identify based on taste and/or the interactions of nursing staff who may have recognized the bottles with the researchers and participants. Outcomes from this study which are pertinent to our review include AE (which we consider to be a subjective outcome) and CDAD (which we consider to be an objective outcome). Because the blinding is unclear we will assess the risk of ‘material’ performance bias in AE (subjective outcome) to be unclear while we consider the risk of ‘material’ performance bias in CDAD (objective outcome) to be low

Blinding of participants and personnel (performance bias)
AE
Unclear riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of participants and personnel (performance bias)
AAD
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of outcome assessment (detection bias)
CDAD
Low risk“Microbiology staff who were blind to the study grouping assessed occurrence of C. difficile by analysis of a stool sample from patients who had diarrhea.” We consider the CDAD outcome to have been assessed blind in this study and the risk of ‘material’ detection bias to be low

Blinding of outcome assessment (detection bias)
AE
Unclear riskIt appears AE were assessed by the participants and reported to study staff. It is unclear if all participants were blind. For the purposes of this review we have classified AE as a subjective outcome and therefore we assess the risk of ‘material’ detection bias for AE to be unclear

Blinding of outcome assessment (detection bias)
AAD
Low riskSee above: Blinding of outcome assessment (detection bias) CDAD

Incomplete outcome data (attrition bias)
CDAD
Low risk“We could not complete follow-up on 16%  (22/135; 12 in probiotic group, 10 in placebo group) as we were unable to contact them at home despite numerous phone calls and written communications (16) or they had withdrawn (6) from the study, thus the analysis for occurrence of antibiotic associated diarrhea included 113 patients (56 in control and 57 in probiotic group). Four patients were not tested for C difficile (one in probiotic group, three in control group) and thus were not included in the analysis for occurrence of diarrhea associated with C difficile.”

The missing data were equally distributed between the two groups and the reasons for the missing data were similar in both groups. The missing data points are less likely to affect the authors’ conclusions regarding the CDAD outcome in a ‘material’ way considering the event rates of 0 to 9

Incomplete outcome data (attrition bias)
AE
High riskSince there were no AE reported and the actual reasons given for dropout were not known for many participants it is possible that different AE rates due to intervention might have led to some dropout and since even a few events would change the results for this outcome (the comparison was 0 to 0) we therefore consider the risk of ‘material’ attrition bias to be high for this outcome

Incomplete outcome data (attrition bias)
AAD
Low riskMissing data were equally distributed between the two groups and the reasons for the missing data were similar in both groups

Selective reporting (reporting bias)High riskThe trial was registered with the National Research Register under ID N0016106821. In the register the outcomes listed were: “Proportion of patients free of diarrhea in active & placebo groups, average length of stay compared in the two groups.”

The outcome of length of hospital stay which was listed in the register was not reported on as an outcome in the paper. Additionally the secondary outcome of CDAD which was listed in the paper was not listed in the register. Finally, the primary outcome of rate of diarrhea was “reported using measurements, analysis methods or subsets of the data (e.g. subscales) that were not pre-specified” (Higgins 2011). This classifies as a high risk of bias according to Higgins. Considering all of these concerns we classify the risk of ‘material’ reporting bias to be high

Other biasUnclear risk“Funding: Healthcare Foundation and Hammersmith Hospital Trustees research committee and Danone Vitapole (Paris, France). The Healthcare Foundation made initial comments on the design of the study. Once funding was agreed none of the funding sources had any role in the data collection, analysis, interpretation of data, writing of the report, or the decision to submit the paper for publication.

“Competing interests: CJB, MH, and ALD’S have received funding from Danone to attend Danone International Conventions on Probiotics. CJB is a member of Danone UK advisory group.

The intervention is a product of Danone. While the study received funding from the producer of the product a clear statement was made regarding the conduct and design of the study. According to our a priori criteria for RoB assessment for funding we consider an industry/sponsor author to be a high risk of bias. In this case an author was a member of an industry/sponsor advisory group as opposed to an employee. The risk of bias in this regard is therefore unclear to us

Imase 2008

MethodsNo treatment control three armed RCT (2 active arms of differing dose), follow-up: days 3 and 7 post treatment


ParticipantsAdult population, NS, Japan, unclear if patients with recurrent C. difficile were included


InterventionsClostridium butyricum CBM588, one group 6 tablets / day x 7 days and one group 12 tablets/day x 7 days or no treatment


OutcomesC. difficile incidence and AAD


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskThe method of randomization was not described

Allocation concealment (selection bias)Unclear riskNo pertinent information provided so it is unclear if allocation was successfully concealed

Blinding of participants and personnel (performance bias)
C. difficile incidence
Unclear riskNo pertinent information provided

Blinding of participants and personnel (performance bias)
AAD
Unclear riskNo pertinent information provided

Blinding of outcome assessment (detection bias)
C. difficile incidence
Unclear riskNo pertinent information provided

Blinding of outcome assessment (detection bias)
AAD
Unclear riskNo pertinent information provided

Incomplete outcome data (attrition bias)
C. difficile incidence
Low riskNo missing outcome data; number randomized is clearly stated and equal to number analysed. The risk of attrition bias is considered to be low for all outcomes

Incomplete outcome data (attrition bias)
AAD
Low riskSee above: Incomplete outcome data (attrition bias) C. difficile incidence

Selective reporting (reporting bias)Low riskNo protocol for this study was identified. The outcomes listed and described in ‘methods’ were those analysed in ‘results’

Other biasHigh riskNo clear statement regarding financial conflict of interest or funding. “CBM588 (MIYA-BM tablets, Miyarisan Pharmaceutical, Tokyo, Japan) is a probiotic agent containing approximately 107 cfu per tablet.”

One of the authors is associated with the company that produces the probiotic tested.  According to our a priori criteria for RoB assessment we will classify this as a high risk of bias

Klarin 2008

MethodsPlacebo controlled RCT, follow-up: 2 times per week while patient was in ICU


ParticipantsAdult population, inpatients (ICU), Sweden, unclear if patients with recurrent C. difficile were included


InterventionsLactobacillus plantarum 299v initially 9.6x 10^11 cfu/day and thereafter 8x10^10 cfu/day or placebo for length of ICU stay


OutcomesC. difficile infection


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskThe method of randomization was not described

Allocation concealment (selection bias)Unclear risk“Randomisation was blinded to the investigators, the ward staff, and the sponsor (Probi AB, Lund, Sweden). Packages of the active and control study products came from an independent company.” This description makes no explicit mention of allocation concealment. There is no indication that the intervention packages were sequentially numbered. Therefore, it is unclear if allocation was successfully concealed

Blinding of participants and personnel (performance bias)
AE
Low risk“Randomization was blinded to the investigators, the ward staff, and the sponsor. Packages of the active and control study products came from an independent company… The active study product consisted of a fermented oatmeal gruel containing 8 _ 108 colony-forming units (CFU)/ml of Lp299v (Probi AB). As a control, the same gruel without Lp299v bacteria but with lactic acid added to achieve the same pH was used… Enteral feeding was carried out”

Blinding of participants and personnel (performance bias)
C. difficile incidence
Low riskSee above: Blinding of participants and personnel (performance bias) AE

Blinding of outcome assessment (detection bias)
AE
Low risk“Identification of C. difficile and testing for toxins were performed at the clinical microbiology departments at the hospitals. Lp299v was analysed in blinded samples… Furthermore, at the Lund University Hospital ICU, a second set of rectal swabs was collected on sampling days and sent blinded to Probi AB for analyses of lactobacilli, Enterobacteriaceae, sulphite-reducing clostridia, enterococci, and total viable count of anaerobes and Gram-negative bacteria”

Blinding of outcome assessment (detection bias)
C. difficile incidence
Low riskSee above: Blinding of outcome assessment (detection bias) AE

Incomplete outcome data (attrition bias)
AE
Low risk“Forty-eight patients were included according to the protocol. Two patients declined participation, and two were excluded because the enteral feeding and the tested product were not given as instructed in the protocol. Thus, a total of 44 patients completed the study; 22 were given the active treatment and 22 received the control product”

Only 8% missing outcome data

Incomplete outcome data (attrition bias)
C. difficile incidence
Low riskSee above: Incomplete outcome data (attrition bias) AE

Selective reporting (reporting bias)Low riskA protocol for this study was not identified. Outcomes not explicitly stated as ‘outcomes’ in ‘methods’ although all those inferred to be outcomes were all reported in ‘results’

Other biasHigh risk“Probi AB provided the study product and performed bacterial analyses as an unconditional grant. Two of the authors, B. J. and G. M., are shareholders in Probi AB.”

Probi AB produces the probiotic being tested. According to our a priori defined criteria for RoB assessment we assess this as a high risk of bias

Koning 2008

MethodsPlacebo controlled RCT, follow-up: days 7, 14, 63


ParticipantsAdult population, outpatient, Netherlands, unclear if patients with recurrent C. difficile were included


InterventionsMultispecies (10) probiotic for total dose of 1x 10^10 cfu/day for 2 weeks or placebo


OutcomesAAD, C. difficile infection and AE


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskThe method of randomization was not described

Allocation concealment (selection bias)Unclear risk“The treatment allocation was concealed to all investigators and volunteers, until the study had been completed and all analyses had been performed.”

While this trial claims that the allocation was concealed there is no description of the methods used for concealment

Blinding of participants and personnel (performance bias)
AE
Low risk“The study was executed according to a parallel, randomized, placebo-controlled, double-blind design”

Blinding of participants and personnel (performance bias)
C. difficile incidence
Low riskSee above: Blinding of participants and personnel (performance bias) AE

Blinding of participants and personnel (performance bias)
AAD
Low riskSee above: Blinding of participants and personnel (performance bias) AE

Blinding of outcome assessment (detection bias)
AE
Low riskThe outcomes of AAD and AE were assessed by the participants who were blinded

Blinding of outcome assessment (detection bias)
C. difficile incidence
Low riskThere is no explicit mention of blinding of the laboratory (e.g. cytotoxin assay) personnel although this is a placebo controlled drug trial so in accordance with our a priori defined RoB criteria we will consider the risk of bias to be low here 

Blinding of outcome assessment (detection bias)
AAD
Low riskSee above: Blinding of outcome assessment (detection bias) AE

Incomplete outcome data (attrition bias)
AE
Low risk“One subject in the probiotic group was found to be allergic to amoxycillin and had to be excluded.. Forty healthy volunteers completed the study” 

Incomplete outcome data (attrition bias)
C. difficile incidence
Low riskThere is no mention of noncompliance with fecal samples and it seems all groups were over 90% compliant with the placebo, intervention and antibiotic. From data representation in the paper it seems these two participants who did not complete the questionnaire were also excluded from analysis. In regards to C. difficile incidence, the two missing outcome data patients were from the placebo group so any unaccounted for C. difficile incidence in these participants would have actually favored the intervention effect estimate

Incomplete outcome data (attrition bias)
AAD
Low riskSee above: Incomplete outcome data (attrition bias) AE

Selective reporting (reporting bias)Low riskA protocol for this study was not identified. Outcomes were not explicitly stated as such in ‘methods’ although all those inferred to be outcomes were all reported in ‘results’

Other biasUnclear riskNo explicit mention of conflict of interest. However, one of the authors is associated with the company that produces the study product. Our a priori defined criteria for assessment of funding bias considers a ‘sponsor’ as author to be a high risk of bias. While a study author is associated with the product being evaluated the funding appears to have come from a government agency. Additionally, no information regarding the roles of each author is provided so it is impossible to assess the role of the author connected to industry in planning the study or analysing the data. So while we identified a conflict of interest not reported in the paper we are unable to assess the role of this in creating ‘material’ bias in the effect estimates 

Kotowska 2005

MethodsPlacebo controlled RCT, follow-up: 2 weeks after last study drug dose


ParticipantsPediatric population, mixed inpatient and outpatient, Poland, unclear if patients with recurrent C. difficile were included


InterventionsS. boulardi 10 x 109 cfu/day or placebo for duration of antibiotic course


OutcomesCDAD, AAD and AE


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Low risk“Investigators at the Medical University of Warsaw used computers to generate independent allocation sequences and randomization lists for each study site. To avoid a disproportionate number of patients in the experimental or placebo group, randomization at each site was performed in blocks of six (three received placebo and three, active treatment)”

Allocation concealment (selection bias)Low risk“To ensure allocation concealment, an independent subject prepared the randomization schedule and oversaw the packaging and labelling of trial treatments”

Blinding of participants and personnel (performance bias)
CDAD
Low risk“All investigators, participants, outcome assessors and data analysts were blinded to the assigned treatment throughout the study”

“The active treatment and placebo used in this study were prepared centrally by the hospital pharmacy at the Medical University of Warsaw as identically appearing wafers”

Blinding of participants and personnel (performance bias)
AE
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of participants and personnel (performance bias)
AAD
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of outcome assessment (detection bias)
CDAD
Low riskOutcome assessors were blinded

Blinding of outcome assessment (detection bias)
AE
Low riskBlinding of outcome assessment (detection bias) CDAD

Blinding of outcome assessment (detection bias)
AAD
Low riskBlinding of outcome assessment (detection bias) CDAD

Incomplete outcome data (attrition bias)
CDAD
Low risk“Overall, 23 (8.6%) of the randomized children [13 (9.8%) in the S. boulardii group and 10 (7.2%) in the placebo group] withdrew before completing the trial and were lost to follow-up. The reasons for not completing the trial were non-acceptance of the allocated intervention (n = 22) or damage of the study product (n = 1).”

 

A relatively low number of participants had missing data post randomization. The missing data was balanced between groups both in number and reasons given for the missing outcome data. Additionally, an extreme case scenario regarding the missing data was calculated by the authors and shown to not influence the authors’ conclusions. While it is unclear from the paper if this extreme case scenario was conducted for outcomes besides AAD (the authors’ primary outcome), we consider the missing data to not realistically have a risk of ‘material’ bias on the authors’ conclusions regarding CDAD

Incomplete outcome data (attrition bias)
AE
Low riskThere were no AE reported in either group. Although an extreme disproportion in AE event rates in the missing outcome data could have affected the estimate of AE it seems highly unlikely based on the rationale given for the missing data, null event rate in both groups, as well as the overall low amount of missing data

Incomplete outcome data (attrition bias)
AAD
Low riskSee above; Incomplete outcome data (attrition bias) CDAD

Selective reporting (reporting bias)Low riskA protocol of this trial was not located. All outcomes listed in ‘methods’ were analysed in ‘results.’ We consider the risk of reporting bias to be low

Other biasUnclear riskBaseline participant characteristics roughly equivalent with no significant differences noted. No financial support, funding, or conflict of interest were listed. According to our a priori criteria for risk of funding bias we consider the risk of bias here to be unclear

Lewis 1998

MethodsPlacebo controlled RCT, follow-up: every four days during length of treatment


ParticipantsAdult (elderly) population, inpatients, Wales, unclear if patients with recurrent C. difficile were included


InterventionsS. boulardii 226 mg/day or placebo for length of antibiotic treatment


OutcomesC. difficile incidence and AAD


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskThe method of randomization was not described

Allocation concealment (selection bias)Unclear riskNo pertinent information is provided so it is unclear if allocation was successfully concealed

Blinding of participants and personnel (performance bias)
C. difficile incidence
Low risk“The trial capsules were prepacked by the pharmacy such that the nursing staff dispensing them were blinded to which medication they were dispensing to the subjects. The medical management of each volunteer was by the attending physician and not influenced by the study”

Blinding of participants and personnel (performance bias)
AAD
Low riskSee above: Blinding of participants and personnel (performance bias) C. difficile incidence

Blinding of outcome assessment (detection bias)
C. difficile incidence
Low riskOutcomes assessed by the nursing staff are assumed to be blinded as the nurses were blinded.  There is no mention of blinding of the cytotoxin assay or cell culture personnel although this is a placebo controlled drug trial so in accordance with our a priori defined RoB criteria we will consider the risk of bias to be low here

Blinding of outcome assessment (detection bias)
AAD
Low riskSee above: Blinding of outcome assessment (detection bias) C. difficile incidence

Incomplete outcome data (attrition bias)
C. difficile incidence
Low risk“Of 81 patients invited to participate in the study, 72 agreed and were randomized. Three subjects failed to complete the study because they did not wish to have stool specimens collected.”

From the presentation of their results it seems 69 participants were included in analysis therefore it seems the missing outcomes data are for the 3 who did not complete the study. It is not clear from which group those three belonged. However, the reason given for the missing outcome data (not wishing to collect stool specimens) is unlikely to be related to the true outcome. Additionally, even assuming high event rates for each outcome from the missing data there would be little effect on the conclusion reached by the study authors. Therefore, we will consider the risk of attrition bias here to be low for all outcomes

Incomplete outcome data (attrition bias)
AAD
Low riskSee above: Incomplete outcome data (attrition bias) C. difficile incidence

Selective reporting (reporting bias)Low riskA protocol for this study was not identified. Outcomes not explicitly stated as such in ‘methods’ although all those inferred to be outcomes were all reported in ‘results’

Other biasLow riskThis paper appears to be free of baseline imbalances and funding conflicts. No other sources of bias identified

Lonnermark 2010

MethodsPlacebo controlled RCT, follow-up: depending on outcome last day of study drug or 3 weeks post treatment


ParticipantsAdult population, mixed inpatient and outpatient, Sweden, unclear if patients with recurrent C. difficile were included


InterventionsL. plantarum 299v 10 x 109 cfu/day or placebo within 48 hours of antibiotic commencement until 7 days after discontinuation


OutcomesCDAD, AAD, AE, and C. difficile incidence


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Low risk“Computer-generated randomization lists were used to allocate patients to either treatment group”

Allocation concealment (selection bias)Low risk“Staff at Ska˚nemejerier, who at no time had direct contact with the patients or investigators, labelled the test drink packages according to the randomization schedule”

Blinding of participants and personnel (performance bias)
CDAD
Low risk“The study was double blind and placebo controlled”

Blinding of participants and personnel (performance bias)
AE
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of participants and personnel (performance bias)
C. difficile incidence
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of participants and personnel (performance bias)
AAD
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of outcome assessment (detection bias)
CDAD
Low riskThe outcomes of diarrhea as well as other secondary outcomes such as A.E. were assessed by the participants who were blinded.  There is no mention of blinding of the cytotoxin assay personnel although this is a placebo controlled drug trial so in accordance with our a priori defined RoB criteria we will consider the risk of bias to be low here

Blinding of outcome assessment (detection bias)
AE
Low riskSee above: Blinding of outcome assessment (detection bias) CDAD

Blinding of outcome assessment (detection bias)
C. difficile incidence
Low riskSee above: Blinding of outcome assessment (detection bias) CDAD

Blinding of outcome assessment (detection bias)
AAD
Low riskSee above Blinding of outcome assessment (detection bias) CDAD

Incomplete outcome data (attrition bias)
CDAD
Unclear risk“Among the 76 patients who left the study, 38 were randomized to L. plantarum 299v and 38 to placebo. The reasons for not completing the study did not differ between these groups of individuals (data not shown). A comparison between the patients who remained in the study and patients who did not is presented in Table 1. The drop-outs were significantly younger than the patients completing the study (P=0.0015).”

 

Missing outcome data balanced in numbers across intervention groups, with similar reasons for missing data across groups (when reasons were known). However, the number of drop outs is very large and we have no reason given for drop out for 31 participants. In addition, event rates were very low for both objective and subjective outcomes. Due to these concerns we will assess as unclear risk of attrition bias for all outcomes

Incomplete outcome data (attrition bias)
AE
Unclear riskSee above: Incomplete outcome data (attrition bias) CDAD

Incomplete outcome data (attrition bias)
C. difficile incidence
Unclear riskSee above: Incomplete outcome data (attrition bias) CDAD

Incomplete outcome data (attrition bias)
AAD
Unclear riskSee above: Incomplete outcome data (attrition bias) CDAD

Selective reporting (reporting bias)Low riskOutcomes clearly stated in ‘methods’ all of which were analysed in ‘results.’

Other biasHigh riskThe study product being investigated in this study is sold by Probi AB. Financial support came from Probi AB. One of the authors is associated with Probi AB. Three authors hold stock in Probi AB.  According to our a priori defined RoB criteria for funding bias we assess this as a high risk of bias

McFarland 1995

MethodsPlacebo controlled RCT, follwo-up: 7 weeks after last study drug dose


ParticipantsAdult population, inpatient, USA, unclear if patients with recurrent C. difficile were included


InterventionsS. boulardi lyophilized 30 x 109 cfu/day or placebo within 72 hours of antibiotic commencement until 3 days after discontinuation


OutcomesCDAD, AAD, AE, and C. difficile incidence


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskThe method of randomization was not described

Allocation concealment (selection bias)Unclear riskNo pertinent information provided

Blinding of participants and personnel (performance bias)
CDAD
Low risk“A double-blinded…trial.”

 

“The appearance and odor of the capsules of the patented S. boulardii and placebo were identical. The 1:1 ( S. boulardii:placebo) randomization and packaging of the blinded study kits was performed at Laboratoires Biocodex (Montrouge, France) to ensure that the study investigators did not have access to the identity of the study drug”

Blinding of participants and personnel (performance bias)
AE
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of participants and personnel (performance bias)
C. difficile incidence
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of participants and personnel (performance bias)
AAD
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of outcome assessment (detection bias)
CDAD
Low risk“The etiology of all cases of diarrhea was determined independently by three blinded investigators.”

The outcomes from this trial pertinent to our review include CDAD, C. diff incidence, and AE. It appears diarrhea and AE were reported by patients to study investigators, all of whom were blinded. In addition, the assessment of CDAD was explicitly described as assessed blinded. While not explicitly mentioned in the text of the paper, it would appear likely that the C. difficile incidence was assessed in a similar blinded manner.For these reasons we consider the risk of ‘material’ detection bias for the outcomes CDAD, C. diff incidence, and AE to be low

Blinding of outcome assessment (detection bias)
AE
Low riskSee above: Blinding of outcome assessment (detection bias) CDAD

Blinding of outcome assessment (detection bias)
C. difficile incidence
Low riskSee above: Blinding of outcome assessment (detection bias) CDAD

Blinding of outcome assessment (detection bias)
AAD
Low riskSee above: Blinding of outcome assessment (detection bias) CDAD

Incomplete outcome data (attrition bias)
CDAD
High riskThere are missing data from 33% of randomized participants. The authors claim that there was no significant difference in study group assignment between those censored and those remaining in the trial. In addition, while censored participants did have significantly different outcomes than the rest of randomized patients (e.g. AAD) the authors claim there was no significant difference based upon the type of study drug assigned. However, the raw numbers of missing outcome data per study group are not provided. Considering the extremely high missing outcome data rate we must consider the risk of ‘material’ attrition bias for the low event rate outcomes of CDAD and C. diff incidence to be high

Incomplete outcome data (attrition bias)
AE
Low risk96% of adverse event forms for all randomized patients were available for analysis. Therefore, we consider the risk of ‘material’ attrition bias to be low for the AE outcome

Incomplete outcome data (attrition bias)
C. difficile incidence
High riskSee above: Incomplete outcome data (attrition bias) CDAD

Incomplete outcome data (attrition bias)
AAD
High riskSee above: Incomplete outcome data (attrition bias) CDAD

Selective reporting (reporting bias)Low riskNo protocol identified. ‘Outcomes’ were not explicitly listed although all outcomes and statistical analyses inferred from the ‘methods’ section were analysed in the ‘results’ section

Other biasHigh riskThis study was free of baseline imbalances.

 

“The study was funded by grants to University of Kentucky, University of Washington, and St. Louis University Medical Center from Laboratoires Biocodex, Montrouge, France.”

The primary author is associated with a company that both produces S. boulardii and funded the trial. According to our a priori determined criteria for risk of funding bias we consider this to constitute a high risk of ‘material’ bias

Miller 2008a

MethodsPlacebo controlled RCT, follow-up: not stated


ParticipantsAdult population, inpatient, Canada, unclear if patients with recurrent C. difficile were included


InterventionsLGG capsules (4 x 1010 cfu /day) or placebo for 14 days


OutcomesCDAD and AE


Notesunpublished


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Low riskFollow up with authors revealed that they used computers for generation of randomization

Allocation concealment (selection bias)Unclear riskNo pertinent information provided, therefore it is unclear if allocation was successfully concealed

Blinding of participants and personnel (performance bias)
CDAD
Low risk“We conducted two randomized, double-blind studies”

Blinding of participants and personnel (performance bias)
AE
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of outcome assessment (detection bias)
CDAD
Low risk“Diarrhea stool was tested for C. difficile toxin.”

 

There is no mention of blinding of the cytotoxin assay personnel although this is a placebo controlled drug trial so we will consider the risk of bias to be low here

Blinding of outcome assessment (detection bias)
AE
Low riskWhile the only AE reported was mortality it was assessed as not related to intervention. Nevertheless mortality is an obviously objective outcome and so for both AE and CDAD we assess the risk of ‘material’ bias to be low

Incomplete outcome data (attrition bias)
CDAD
Low riskNo loss to follow up

Incomplete outcome data (attrition bias)
AE
Low riskSee above: Incomplete outcome data (attrition bias) CDAD

Selective reporting (reporting bias)Unclear riskNo protocol identified. This was an unpublished abstract so unclear if methods section would match with results section. We consider the risk of ‘material' reporting be unclear

Other biasHigh riskConagra supported the study and produces the product. It is unclear what role or access Conagra had with design, conduct, and analysis of the studies. 

 

“Dr. Miller has received research grants, acts as a consultant, or serves on an advisory board for the following: Biomerieux, ConAgra, Convatec, Genzyme, Iroko, Merck, Novartis, Optimer, Salix, Wyeth.”

Primary author has financial relationship with the company funding the trials and producing the trial intervention. According to our a priori defined criteria for RoB assessment we assess this as a high risk of bias

Miller 2008b

MethodsPlacebo controlled RCT, follow-up: not stated


ParticipantsAdult population, inpatient, Canada, unclear if patients with recurrent C. difficile were included


Interventions 

LGG 12 x 1010 cfu /day or placebo for 14 days


OutcomesCDAD, AAD and AE


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Low riskFollow up with authors revealed that they used computers for generation of randomization

Allocation concealment (selection bias)Unclear riskNo pertinent information provided, therefore it is unclear if allocation was successfully concealed

Blinding of participants and personnel (performance bias)
CDAD
Low risk“We conducted two randomized, double-blind studies”

Blinding of participants and personnel (performance bias)
AE
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of participants and personnel (performance bias)
AAD
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of outcome assessment (detection bias)
CDAD
Low risk“Diarrhea stool was tested for C. difficile toxin.”

There is no mention of blinding of the cytotoxin assay personnel although this is a placebo controlled drug trial so we will consider the risk of bias to be low here

Blinding of outcome assessment (detection bias)
AE
Low riskWhile the only AE reported was mortality it was assessed as not related to intervention. Nevertheless mortality is an obviously objective outcome and so for both AE and CDAD we assess the risk of ‘material’ bias to be low

Blinding of outcome assessment (detection bias)
AAD
Low riskDiarrhea assessment was from blinded personnel

Incomplete outcome data (attrition bias)
CDAD
Unclear riskThere is some confusion in abstract and materials provided by authors. In Miller 2008b the abstract says there was 1 LTFU in the LGG group and 4 in placebo group. But it also says by the end there were 3 LTFU. It is unclear if these are additional LTFU and what group the 3 were in. Communication with authors could not resolve this

Incomplete outcome data (attrition bias)
AE
Unclear riskSee above: Incomplete outcome data (attrition bias) CDAD

Incomplete outcome data (attrition bias)
AAD
Unclear riskSee above: Incomplete outcome data (attrition bias) CDAD

Selective reporting (reporting bias)Unclear riskNo protocol identified. This was an unpublished abstract so unclear if methods section would match with results section. We consider the risk of ‘material' reporting be unclear

Other biasHigh riskConagra supported the study and produces the product. It is unclear what role or access conagra had with design, conduct, and analysis of the studies. 

 

“Dr. Miller has received research grants, acts as a consultant, or serves on an advisory board for the following: Biomerieux, ConAgra, Convatec, Genzyme, Iroko, Merck, Novartis, Optimer, Salix, Wyeth.”

 

Primary author has financial relationship with the company funding the trials and producing the trial intervention. According to our a priori defined criteria for RoB assessment we assess this as a high risk of bias

Nord 1997

MethodsPlacebo controlled RCT, follow-up: 21 days post antibiotic treatment


ParticipantsAdult population, healthy, Sweden, unclear if patients with recurrent C. difficile were included


InterventionsBifidobacterium bifidum and Lactobacillus acidophilus 2x10^10 cfu/day or placebo for 14 days


OutcomesC. difficile incidence and AE


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskThe method of randomization was not described

Allocation concealment (selection bias)Unclear riskNo pertinent information provided, therefore it is unclear if allocation was successfully concealed 

Blinding of participants and personnel (performance bias)
AE
Low risk“The investigation was performed as a randomized double-blind parallel group study…”

Blinding of participants and personnel (performance bias)
C. difficile incidence
Low riskSee above: Blinding of participants and personnel (performance bias) AE

Blinding of outcome assessment (detection bias)
AE
Low riskThe outcomes pertinent to our review from this trial include AE and C. difficile incidence.  It appears AE were observed by study personnel and/or reported to them by the participants all of which were blinded. There is no explicit mention of blinding of laboratory personnel who would have assessed the C. difficile incidence outcome. However, this is a placebo controlled drug trial so in accordance with our a priori defined RoB criteria we will consider the risk of bias to be low here

Blinding of outcome assessment (detection bias)
C. difficile incidence
Low riskBlinding of outcome assessment (detection bias) AE

Incomplete outcome data (attrition bias)
AE
Low riskIt appears all outcome data were available from all randomized participants

Incomplete outcome data (attrition bias)
C. difficile incidence
Low riskSee above: Incomplete outcome data (attrition bias) AE

Selective reporting (reporting bias)Low riskNo protocol identified and no explicit listing of “outcomes” in the ‘methods’ section. However, all assumed outcomes discussed in ‘methods’ were analysed in ‘results’

Other biasUnclear riskNo other source of bias identified. No mention of funding source. According to our a priori criteria for RoB assessment we will assess this as an unclear risk of bias

Plummer 2004

MethodsPlacebo controlled RCT, follow-up: last day of study drug


ParticipantsAdult population (elderly), inpatient, England, unclear if patients with recurrent C. difficile were included


InterventionsL. acidophilus and B. bifidum 20 x 109 cfu/day or placebo within 36 hours of antibiotic commencement then for 20 days


OutcomesCDAD, AAD and C. difficile incidence


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskThe method of randomization was not described

Allocation concealment (selection bias)Unclear riskNo pertinent information provided and so it is unclear if allocation was successfully concealed

Blinding of participants and personnel (performance bias)
CDAD
Low risk“The trial was a double blind, placebo-controlled study…”

Blinding of participants and personnel (performance bias)
C. difficile incidence
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of participants and personnel (performance bias)
AAD
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of outcome assessment (detection bias)
CDAD
Low riskThe outcomes of this study pertinent to our review include CDAD and C. difficile incidence. Both of these outcomes were assessed via culture and immunologic laboratory measures. There is no mention of blinding of the laboratory personnel although this is a placebo controlled drug trial so in accordance with our a priori defined RoB criteria we will consider the risk of bias to be low here

Blinding of outcome assessment (detection bias)
C. difficile incidence
Low riskSee above: Blinding of outcome assessment (detection bias) CDAD

Blinding of outcome assessment (detection bias)
AAD
Low riskSee above: Blinding of outcome assessment (detection bias) CDAD

Incomplete outcome data (attrition bias)
CDAD
Low risk“Of the randomised patients, 138 completed the study, 69 with probiotics in conjunction with antibiotics and 69 with antibiotics alone.”

“150 patients were recruited and 138 patients fulfilled the inclusion criteria. For these patients, bowel habit on admission and prescribed medication were recorded.”

 

It appears that for all eligible participants that were randomized all outcome data was available. We consider the risk of ‘material’ attrition bias to be low for all outcomes.

Incomplete outcome data (attrition bias)
C. difficile incidence
Low riskSee above: Incomplete outcome data (attrition bias) CDAD

Incomplete outcome data (attrition bias)
AAD
Low riskSee above: Incomplete outcome data (attrition bias) CDAD 

Selective reporting (reporting bias)Low riskNo protocol identified. No explicit disclosure of ‘outcomes’ to be addressed although all inferred outcomes from ‘methods’ section were analyzed in ‘results’

Other biasHigh riskThere is no direct mention of study funding although it is disclosed that the study product was provided by Cultech. The primary author is an employee of the company (Cultech) that produces the study product. Although funding is not explicitly disclosed, we consider it likely that the trial was funded by Cultech. Due to these considerations we consider the risk of ‘material’ bias here to be high

Pozzoni 2012

MethodsPlacebo controlled RCT, follow-up: 12 weeks after last antibiotic dose


ParticipantsAdult population (> 50 years of age), inpatient, Italy, unclear if patients with recurrent C. difficile were included


InterventionsSaccharomyces Boulardii 10x109 cfu/day or placebo within 48 hours of antibiotic commencement for length of antibiotic treatment and then for 7 days afterwards


OutcomesCDAD, AAD, and AE


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Low risk"...computer-generated random-number table"

Allocation concealment (selection bias)Low risk"Central randomisation by hospital pharmacy.."

Blinding of participants and personnel (performance bias)
CDAD
Low risk"The S. boulardii and placebo tablets were identical in shape, size, taste, smell, and color. The participants, researchers, and staff contributing to the study (doctors, nurses, and microbiologists) were unaware of the treatment allocations throughout the duration of the study"

Blinding of participants and personnel (performance bias)
AE
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of participants and personnel (performance bias)
AAD
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of outcome assessment (detection bias)
CDAD
Low risk"The participants, researchers, and staff contributing to the study (doctors, nurses, and microbiologists) were unaware of the treatment allocations throughout the duration of the study"

Blinding of outcome assessment (detection bias)
AE
Low riskSee above: Blinding of outcome assessment (detection bias) CDAD

Blinding of outcome assessment (detection bias)
AAD
Low riskSee above: Blinding of outcome assessment (detection bias) CDAD

Incomplete outcome data (attrition bias)
CDAD
High risk25% of patients in the treatment group were lost to follow-up and 27% of placebo patients were lost to follow-up.

It appears that patients were only evaluated for C. difficile if the diarrhea occurred in the hospital.

It seems only 29 patients developed diarrhea. Of these 22, developed diarrhea out of hospital and only 2 patients were tested for C. difficile. Therefore 20/29 cases of diarrhea were not tested for C. difficile

Incomplete outcome data (attrition bias)
AE
Low riskAll patients who discontinued where investigated for rationale and none reported withdrawal due to AE

Incomplete outcome data (attrition bias)
AAD
Unclear riskHigh LTFU, unclear what effect this has on AAD outcome

Selective reporting (reporting bias)Low riskThe study is registered under ISRCTN number ISRCTN86623192 ( http://www.controlled-trials.com/ISRCTN86623192/). The reported outcomes are identical to those published in protocol

Other biasLow riskThis study was supported financially by an ad hoc hospital fund for independent research.

No funding biases noted. No significant baseline differences between groups

Psaradellis 2010

MethodsPlacebo controlled RCT, follow-up: 3 weeks after last study drug dose


ParticipantsAdult population, mixed inpatient and outpatient, Canada, unclear if patients with recurrent C. difficile were included


InterventionsPlacebo or L. acidophilus CL1285 and L. casei 25 x 109 cfu/day for 2 days then 50 x 109 cfu/day until 5 days after discontinuation of antibiotic


OutcomesCDAD, AAD, and AE


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskThe method of randomization was not described

Allocation concealment (selection bias)Unclear riskNot enough information provided

Blinding of participants and personnel (performance bias)
CDAD
Low risk“This was a multicenter double-blind, randomized, placebo controlled, study…”

Blinding of participants and personnel (performance bias)
AE
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of participants and personnel (performance bias)
AAD
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of outcome assessment (detection bias)
CDAD
Low riskThere is no explicit mention of outcome assessor blinding. Outcomes of interest to our review from this trial include AE and CDAD. There is no mention of blinding of the cytotoxin assay personnel although this is a placebo controlled drug trial so we will consider the risk of bias to be low here 

Blinding of outcome assessment (detection bias)
AE
Low risk“Safety was assessed by the incidence of treatment emergent adverse events, which were reported according to the MedDRA (version 10.1) dictionary of terms.”

It appears AE were assessed by participants reporting to study personal all of whom were blinded and that an objective dictionary of terms was used for reported adverse events

Blinding of outcome assessment (detection bias)
AAD
Low riskDiarrhea assessed by blinded individuals

Incomplete outcome data (attrition bias)
CDAD
High risk“Among the 472 randomized patients, 29 patients were excluded from the ITT analysis due to antibiotic treatment duration of less than 3 days and 6 patients were excluded because diarrhea onset occurred before initiation of study treatment. Therefore a total of 437 (92.6%) were included in the ITT population…”

“There were 16 patients in the BIO K+ group and 30 in the placebo group that underwent CDAD testing. Of these, 1 (6.2%) patient in the BIO K+ group and 4 (13.3%) in the placebo group were positive for the C. difficile toxins (odds ratio = 0.433, p = 0.645).”

The missing data results from less than 10% of the participants and the numbers and reasons for those being excluded are balanced across groups. However, a 2:1 difference in sampling for CDAD is apparent and not representative of the difference in occurrence of AAD between groups. Therefore we must conclude a high risk of ‘material’ bias from incomplete and unbalanced outcome data for the CDAD outcome    

Incomplete outcome data (attrition bias)
AE
Low riskThe missing data results from less than 10% of the participants and the numbers and reasons for those being excluded are balanced across groups. Therefore we are not concerned about attrition bias as it relates to the AE outcomes

Incomplete outcome data (attrition bias)
AAD
Low riskSee above: Incomplete outcome data (attrition bias) AE

Selective reporting (reporting bias)Low riskWhile not reported in the full text article a protocol was discovered on clinicaltrials.gov. The primary outcome listed in the protocol was reported on in the paper. However a secondary outcome listed in the protocol was not mentioned in the paper: “Health outcome evaluation will look at the direct medical costs and clinical outcomes of alternative strategies in the prevention of antibiotic-associated diarrhea in hospitalized adult patients.” Additionally, the primary outcome was secondarily analysed using statistical adjustments not prespecified in the protocol. However the unadjusted results are reported as well both in the body and abstract of the paper. We do not consider these concerns sufficient to consider the risk of ‘material’ reporting bias to be high. We therefore assess the risk of material bias here as low

Other biasUnclear risk“The patient demographics and baseline characteristics were similar for the BIO K+ and placebo groups”

 

“John S. Sampalis and Eliofotisti Psaradellis are employees of JSS Medical Research Inc.; JSS Medical Research Inc. was paid by BIO K+ International Inc. to conduct and manage this study. JSS Medical Research Inc. was responsible for analyzing and interpreting the data as well as writing and reviewing the manuscript. The study was funded by a grant-in-aid of research from BIO K+ International Inc.”

 

Both study authors are employed by a CRO which was paid by the company (Bio K+) which produces the study product.

Rafiq 2007

MethodsRCT (control group not stated), follow-up: not stated


ParticipantsNS, inpatient, USA, unclear if patients with recurrent C. difficile were included


InterventionsL. acidophilus 80%, L. bulgaricus 10%, B. bifidum 5%, S. thermophilus 5%. 3g/day with start of antibiotic until hospital discharge


OutcomesCDAD


Notesunpublished


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskThe method of randomization was described

Allocation concealment (selection bias)Unclear riskInformation not provided

Blinding of participants and personnel (performance bias)
CDAD
Unclear riskNo mention of blinding in abstract and multiple contact attempts with author were unsuccessful. While AE were mentioned in abstract results regarding this outcome were not reported so the only relevant outcome for our review is CDAD

Blinding of outcome assessment (detection bias)
CDAD
Low riskThere is no mention of blinding of the cytotoxin assay personnel although this is a placebo controlled drug trial so we will consider the risk of bias to be low here

Incomplete outcome data (attrition bias)
CDAD
Unclear riskNo mention of loss to follow-up in abstract and multiple contact attempts with author were unsuccessful. We are uncertain if there was incomplete outcome data and must assess as unclear 

Selective reporting (reporting bias)Unclear riskNo protocol identified. This is an abstract so unable to determine predefined outcomes from methods section for comparison with results

Other biasUnclear riskNo information regarding funding is provided. According to our a priori defined criteria for RoB assessment we assess this as an unclear risk of bias

Ruszczynski 2008

MethodsPlacebo controlled RCT, follow-up: 2 weeks after last study drug


ParticipantsPediatric population, mixed inpatient and outpatient, Poland, unclear if patients with recurrent C. diff were included


InterventionsL. rhamnosus GG (2593, 2594, 2595) 2 x 1010 cfu/day or placebo for duration of antibiotic course


OutcomesCDAD, AAD, and AE


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Low riskThe study authors claim to have followed the protocol of an earlier study conducted by their research group (Kotowska 2005).

“Investigators at the Medical University of Warsaw used computers to generate independent allocation sequences and randomization lists for each study site. To avoid a disproportionate number of patients in the experimental or placebo group, randomization at each site was performed in blocks of six (three received placebo and three, active treatment).” (Kotowska 2005)

Allocation concealment (selection bias)Low risk“To ensure allocation concealment, an independent subject prepared the randomization schedule and oversaw the packaging and labelling of trial treatments”

Blinding of participants and personnel (performance bias)
CDAD
Low risk“This was a double-blind, randomized, placebo-controlled, clinical trial…”

“All investigators, participants, outcome assessors and data analysts were blinded to the assigned treatment throughout the study”

Blinding of participants and personnel (performance bias)
AE
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of participants and personnel (performance bias)
AAD
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of outcome assessment (detection bias)
CDAD
Low risk“All investigators, participants, outcome assessors and data analysts were blinded to the assigned treatment throughout the study”

Blinding of outcome assessment (detection bias)
AE
Low riskSee above: Blinding of outcome assessment (detection bias) CDAD

Blinding of outcome assessment (detection bias)
AAD
Low riskSee above: Blinding of outcome assessment (detection bias) CDAD

Incomplete outcome data (attrition bias)
CDAD
Low risk“Of the 240 children recruited in the study, we assigned 120 children to receive L. rhamnosus and 120 to receive the placebo. Overall, three of the randomized children (one in the probiotic group and two in the placebo group) discontinued the study intervention and started to use one of the commercially available probiotic products. However, no patient was lost to follow-up. Thus, all 240 children enrolled were available for the analysis”

Incomplete outcome data (attrition bias)
AE
Low riskSee above: Incomplete outcome data (attrition bias) CDAD

Incomplete outcome data (attrition bias)
AAD
Low riskSee above: Incomplete outcome data (attrition bias) CDAD

Selective reporting (reporting bias)Low riskAll primary and secondary outcomes were clearly identified in the ‘methods’ section and analysed in the ‘results’ section. In addition the study authors claim to have followed the protocol of an earlier study from their group (Kotowska 2005). The outcomes in that earlier paper were identical

Other biasLow risk“The study products were supplied by Biomed (Lublin, Poland), who had no role in the conception, design, or conduct of the study or in the analysis or interpretation of the data. Randomization codes were secured until all data entry was complete and data were analysed. The probiotic combination used in this study is commercially available as Lakcid Forte.”

 

“Declaration of funding interests: This study was funded in part by Biomed, Lublin, Poland, and the Medical University of Warsaw (Research Agreement UKI ⁄ 224 ⁄ 2004).”

 

This study appeared free of gross baseline imbalances between groups.

 

This study was partially funded by industry but there was a clear declaration of non-involvement and access to study design, conduct etc. According to our a priori defined criteria for funding bias we consider this a low risk of ‘material’ bias

Safdar 2008

MethodsPlacebo controlled RCT, follow-up: not stated


ParticipantsAdult population, inpatient, USA, unclear if patients with recurrent C. difficile were included


InterventionsL. acidophilus 60 x 109 cfu/day or placebo during and 14 days after antibiotic course


OutcomesCDAD, AAD, and AE


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskThe method of randomization was not described

Allocation concealment (selection bias)Unclear riskNot enough information provided so it is unclear if allocation was successfully concealed

Blinding of participants and personnel (performance bias)
CDAD
Low risk“This was a double-blind randomized placebo-controlled trial…”

 

“Patients and investigators were unaware of treatment assignment”

Blinding of participants and personnel (performance bias)
AE
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of participants and personnel (performance bias)
AAD
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of outcome assessment (detection bias)
CDAD
Low riskThere is no explicit mention of blinding of ‘outcome assessors.’ There is no mention of blinding of the cytotoxin assay personnel although this is a placebo controlled drug trial so in accordance with our a priori defined RoB criteria we will consider the risk of bias to be low here

Blinding of outcome assessment (detection bias)
AE
Low riskIt appears AE was assessed by participants reporting to personnel all of whom were blinded

Blinding of outcome assessment (detection bias)
AAD
Low riskIt appears diarrhea was assessed by participants reporting to personnel all of whom were blinded

Incomplete outcome data (attrition bias)
CDAD
Low risk“Analyses were intention-to-treat.”

 

“Between November 2003 and June 2005, 40 subjects were enrolled and were randomized, 23 to Florajen and 17 to placebo. One subject on placebo withdrew at his request and thus, 23 patients took Florajen and 16 took placebo.”

 

C. difficile toxin was obtained only for seven patients with diarrhea. It was positive in one and negative in six cases. The one positive case of C. difficile diarrhea occurred in a patient randomized to placebo. The six negative cases were evenly distributed in the two study groups.”

 

10 participants developed diarrhea. However only 7 of them were tested for C. difficile. Of the three that were not tested 2 were from the placebo group and one was from active group. It seems unlikely to us that this could have led to a ‘material’ bias that would have affected the authors’ conclusions regarding the CDAD outcome. We consider the risk of ‘material’ bias for the CDAD outcome to be low  

Incomplete outcome data (attrition bias)
AE
Low risk“Two subjects in the Florajen group and five in the placebo group reported adverse effects.”

Analysis was intention-to-treat. It appears one participant withdrew from the study. There was no loss to follow up. We consider the risk of attrition bias for the AE outcome to be low

Incomplete outcome data (attrition bias)
AAD
Low risk“Analyses were intention-to-treat.”

 

“Between November 2003 and June 2005, 40 subjects were enrolled and were randomized, 23 to Florajen and 17 to placebo. One subject on placebo withdrew at his request and thus, 23 patients took Florajen and 16 took placebo.”

Selective reporting (reporting bias)Low riskNo protocol for this study was identified. The outcomes listed and described in ‘methods’ were those analysed in ‘results’

Other biasUnclear riskThis study was free of baseline imbalances. 

 

“We thank American Lifeline for providing study medication and placebo.”

 

No authors were associated with the company which produces the product being investigated. There is no explicit mention of study funding besides the provision of placebo and study medication. According to our a priori determined criteria for RoB we consider the lack of adequate funding disclosure to constitute an unclear risk of ‘material’ bias

Selinger 2011

MethodsPlacebo controlled RCT, follow-up: 3 weeks after last study drug dose


ParticipantsAdult population, inpatient, United Kingdom, unclear if patients with recurrent C. difficile were included


InterventionsVSL #3 (B. breve, B. longum, B. infantis, L. acidophilus, L. plantarum, L. paracasei, L. bulgaricus, S. thermophilus) 900 x 109  cfu/day or placebo during and 7 days after antibiotic course


OutcomesCDAD, AAD and AE


Notesinterim analysis


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskThe method of randomization was not described

Allocation concealment (selection bias)Unclear riskNo relevant information provided

Blinding of participants and personnel (performance bias)
CDAD
Low riskQuote: “This multi-centre, randomised, double-blind, placebo-controlled trial…”

 

Comment: Adequate blinding of participants and personnel. Risk of ‘material’ performance bias judged to be low.

Blinding of participants and personnel (performance bias)
AE
Low riskQuote: “This multi-centre, randomised, double-blind, placebo-controlled trial…”

 

Comment: Adequate blinding of participants and personnel. Risk of ‘material’ performance bias judged to be low.

Blinding of participants and personnel (performance bias)
AAD
Low risk“This multi-centre, randomised, double-blind, placebo-controlled trial…”

Blinding of outcome assessment (detection bias)
CDAD
Low risk“Masking: Double Blind (Subject, Caregiver, Investigator, Outcomes Assessor)”

 

Protocol identified on clinicaltrials.gov NCT00973908. Protocol indicated outcome assessors were blinded.

Blinding of outcome assessment (detection bias)
AE
Low riskSee above: Blinding of outcome assessment (detection bias) CDAD

Blinding of outcome assessment (detection bias)
AAD
Low riskSee above: Blinding of outcome assessment (detection bias) CDAD

Incomplete outcome data (attrition bias)
CDAD
Low riskContact with author was able to provide ITT data. No cases of CDAD were reported in both groups of all randomized participants

Incomplete outcome data (attrition bias)
AE
Low riskSee above: Incomplete outcome data (attrition bias) CDAD

Incomplete outcome data (attrition bias)
AAD
Low riskSee above: Incomplete outcome data (attrition bias) CDAD

Selective reporting (reporting bias)Low riskProtocol identified on clinicaltrials.gov NCT00973908. All outcomes reporting in protocol are reported in analysis of interim abstract

Other biasUnclear riskThis is an interim analysis of a not fully recruited study. Abstract claims baseline demographics are grossly similar

Shimbo 2005

MethodsNo treatment control RCT, follow-up: up to 22 days after starting study drug


ParticipantsAdult population, outpatients, China, unclear if patients with recurrent C. difficile were included


InterventionsClostridium butyricum MIYAIRI 588, 360 mg/day for 1 week prior to eradication therapy for 14 days


OutcomesC. difficile incidence, AAD and AE


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskThe method of randomization was not described

Allocation concealment (selection bias)Unclear riskNo pertinent information provided

Blinding of participants and personnel (performance bias)
AE
Unclear risk“The patients were blindly and randomly allocated to two groups.”

 

The study claims the participants were blindly allocated. It is unclear but assumed this refers to blinding of patients to what group they were in. However there was no placebo. The arms were standard therapy versus standard therapy plus probiotics.  There is no further explanation as to how the medications were dispensed so it is unclear if blinding could have been assured. Also there is no statement on blinding of study personnel and no mention of double blinding or double dummy. We must assess the risk of ‘material’ performance bias to be unclear for both C. difficile incidence and AE

Blinding of participants and personnel (performance bias)
C. difficile incidence
Unclear riskSee above: Blinding of participants and personnel (performance bias) AE

Blinding of participants and personnel (performance bias)
AAD
Unclear riskSee above: Blinding of participants and personnel (performance bias) AE

Blinding of outcome assessment (detection bias)
AE
Unclear riskNo pertinent information provided

Blinding of outcome assessment (detection bias)
C. difficile incidence
Unclear riskSee above: Blinding of outcome assessment (detection bias) AE

Blinding of outcome assessment (detection bias)
AAD
Unclear riskSee above: Blinding of outcome assessment (detection bias) AE

Incomplete outcome data (attrition bias)
AE
Unclear riskNo pertinent information provided

Incomplete outcome data (attrition bias)
C. difficile incidence
Unclear riskSee above:Incomplete outcome data (attrition bias) AE

Incomplete outcome data (attrition bias)
AAD
Unclear riskSee above:Incomplete outcome data (attrition bias) AE

Selective reporting (reporting bias)Low riskNo protocol identified. All outcomes discussed in the ‘methods’ section were analysed in the ‘results’ section

Other biasUnclear riskThere is no mention of a funding source. According to our a priori determined RoB criteria for funding bias we consider this an unclear risk of ‘material’ bias

Siitonen 1990

MethodsPlacebo controlled RCT, follow-up: last day of treatment


ParticipantsAdult population, age not stated, Finland, unclear if patients with recurrent C. difficile were included


InterventionsLGG yogurt 250 ml/day or placebo for 7 days


OutcomesAE and C. difficile incidence


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskThe method of randomization was not described

Allocation concealment (selection bias)Unclear riskNo pertinent information provided and so it is unclear if allocation was successfully concealed

Blinding of participants and personnel (performance bias)
AE
Low riskThere is no mention of blinding in this study. However this is a placebo controlled drug trial and so in accordance with our a priori determined RoB criteria for performance bias we will consider this as constituting a low risk of ‘material’ performance bias

Blinding of participants and personnel (performance bias)
C. difficile incidence
Low riskSee above: Blinding of participants and personnel (performance bias) AE

Blinding of outcome assessment (detection bias)
AE
Low riskThere is no mention of blinding in this study. However this is a placebo controlled drug trial and so in accordance with our a priori determined RoB criteria for detection bias we will consider this as constituting a low risk of ‘material’ detection bias

Blinding of outcome assessment (detection bias)
C. difficile incidence
Low riskSee above: Blinding of outcome assessment (detection bias) AE

Incomplete outcome data (attrition bias)
AE
Low riskIt appears there are no missing outcome data

Incomplete outcome data (attrition bias)
C. difficile incidence
Low riskSee above: Incomplete outcome data (attrition bias) AE

Selective reporting (reporting bias)Low riskA protocol for this study was not identified. Outcomes were not explicitly mentioned as such but all inferred outcomes discussed in ‘methods’ were reported in ‘results’

Other biasHigh riskFour authors are associated with either Valio Finnish Co-operative Dairies’ Association or Orion Pharmaceutica. Lactobacillus is an organism found in many fermented dairy products. Orion is an industry that promotes and sells products with Lactobacillus GG which was the study intervention. There is no explicit mention of funding in this trial. However we believe it is likely this study was sponsored by either of the two aforementioned companies. We believe the conflict of interest and likely funding bias makes the risk of ‘material’ bias high

Sullivan 2004

MethodsPlacebo controlled RCT, follow-up: up to 1 month after start of treatment


ParticipantsAdult population, inpatients, Sweden, unclear if patients with recurrent C. difficile were included


Interventions20 x 10^9 cfu/day Lactobacillus paracasei spp. paracasei F19 or placebo for 14 days


OutcomesC. difficile incidence and AE


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskThe method of randomization was not described

Allocation concealment (selection bias)Unclear riskNo pertinent information provided so it is unclear if allocation was successfully concealed

Blinding of participants and personnel (performance bias)
AE
Low risk“The two treatment groups were randomized into one placebo and one active group regarding the probiotic supplement in a double-blind fashion.”

 

“A similar product was given to patients in the placebo groups but with no added microorganisms”

Blinding of participants and personnel (performance bias)
C. difficile incidence
Low riskSee above: Blinding of participants and personnel (performance bias) AE

Blinding of outcome assessment (detection bias)
AE
Low riskIt is assumed that AE were reported either by participants to personnel or observed by personnel all of whom where blinded. Therefore, we consider the AE outcome to have been assessed blind   

Blinding of outcome assessment (detection bias)
C. difficile incidence
Low riskassay personnel although this is a placebo controlled drug trial so in accordance with our a priori determined RoB criteria we will consider the risk of bias to be low here 

Incomplete outcome data (attrition bias)
AE
High risk44% of randomized participants did not complete the study and therefore had missing outcome data. This high missing outcome percentage leads us to consider the risk of ‘material’ attrition bias to be high for all outcomes 

Incomplete outcome data (attrition bias)
C. difficile incidence
High riskSee above: Incomplete outcome data (attrition bias) AE

Selective reporting (reporting bias)Low riskA protocol of this trial was not located. All outcomes listed in ‘methods’ were analysed in ‘results.’ We consider the risk of reporting bias to be low

Other biasUnclear riskNo financial support, funding, or conflict of interest were listed. According to our a priori criteria for risk of funding bias we consider the risk of bias here to be unclear

Surawicz 1989

MethodsPlacebo controlled RCT, follow-up: Mean 17.3 days (SD 8.6)


ParticipantsAdult population, inpatients, USA, unclear if patients with recurrent C. difficile were included


InterventionsS. boulardi lyophilized 20 x 109cfu/day or placebo within 48 hours of antibiotic commencement until 2 weeks after discontinuation


OutcomesCDAD, AAD, AE, and C. difficile incidence


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskThe method of randomization was not described

Allocation concealment (selection bias)Unclear riskNo pertinent information provided and so it is unclear if allocation was successfully concealed

Blinding of participants and personnel (performance bias)
CDAD
Low riskQuotes: “The study was performed double-blindly.”

 

“The placebo was an inert composition formulated to be indistinguishable from the capsules of yeast”

Blinding of participants and personnel (performance bias)
AE
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of participants and personnel (performance bias)
C. difficile incidence
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of participants and personnel (performance bias)
AAD
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of outcome assessment (detection bias)
CDAD
Low riskC. difficile and the presence of C. difficile in those patients with diarrhea (CDAD) were determined via culture and toxin assay laboratory methods. There is no mention of blinding of the laboratory personnel although this is a placebo controlled drug trial so in accordance with our a priori defined RoB criteria we will consider the risk of bias to be low here

Blinding of outcome assessment (detection bias)
AE
Low riskWhile the diarrhea outcome was observed by study personnel as well as reported by participants to study personnel it is unclear how AE were assessed. While we consider this outcome to be a ‘subjective’ outcome which may be more susceptible to inadequate blinding we assume AE were reported by participants to trial personnel all of whom were blinded. So despite lack of clarity in the reporting of AE outcome assessment and its subjective nature we consider the overall risk of ‘material’ detection bias for AE to be low

Blinding of outcome assessment (detection bias)
C. difficile incidence
Low riskSee above: Blinding of outcome assessment (detection bias) CDAD

Blinding of outcome assessment (detection bias)
AAD
Low riskSee above: Blinding of outcome assessment (detection bias) CDAD

Incomplete outcome data (attrition bias)
CDAD
High risk“Of the 318 patients enrolled, 138 could not be evaluated for the following reasons: never received study drug or missed >3 doses (26 patients), developed diarrhea within 24 h of starting study (15 patients) or ˜72 h of antibiotic therapy (12 patients), exclusion drug started (9 patients], radiation therapy started (2 patients), or were monitored for <8 days (74 patients).”

 

There is missing outcome data on 43% of randomized participants. This represents a potential for bias especially with the low reported event rate outcomes of CDAD and AE. While some of the missing data appears to have been due to randomized participants not being eligible for the trial due to predefined eligibility criteria there is still a large number of participants with missing outcomes data not due to exclusion criteria. The breakdown of how many missing outcome participants randomized into each group is unclear.  Additionally, not all of the 180 evaluated participants were evaluated for C. diff (138 of 180 were). For all of these reasons we consider the risk of ‘material’ attrition bias to be high in all outcomes  

Incomplete outcome data (attrition bias)
AE
High riskSee above: Incomplete outcome data (attrition bias) CDAD

Incomplete outcome data (attrition bias)
C. difficile incidence
High riskSee above: Incomplete outcome data (attrition bias) CDAD

Incomplete outcome data (attrition bias)
AAD
High riskSee above: Incomplete outcome data (attrition bias) CDAD

Selective reporting (reporting bias)Unclear riskNo protocol identified.

 

“The effectiveness of diarrhea prevention by the yeast was also evaluated in two subgroups of the study population: patients not receiving nasogastric tube feeding and patients infected with C. difficile. Patients on nasogastric tube feeding constituted a population with an increased risk of diarrhea (discussed later), and we wanted to evaluate patients in the absence of this risk factor for diarrhea. When patients who received tube feedings were eliminated from the calculations, the rate of diarrhea in the S. boulardii group was 5 of 109 (4.6%) compared with 13 of 59 (22%) for placebo (Figure 1); x2 = 10.42, P < 0.001.”

‘Outcomes’ were not explicitly listed as such in the methods section. Therefore it is difficult to assess whether apparent subgroup analyses such as that evaluating participants with naso-gastric tubes separately constitute “one or more primary outcomes [being] reported using measurements, analysis methods or subsets of the data (e.g. subscales) that were not pre-specified.” (Higgins 2011). We therefore consider the risk of ‘material’ reporting bias to be unclear

Other biasLow riskBaseline differences appeared roughly equivalent for the variables analysed.

 

“This work was supported by a grant from Laboratoire Biocodex. Montrouge, France.”

 

Sponsor acknowledged but no author is associated with sponsor. According to our a priori determined criteria for RoB assessment we consider the risk of ‘material’ bias to be low here

Thomas 2001

MethodsPlacebo controlled RCT, follow-up: 7 days after last study drug dose


ParticipantsAdult population, inpatient, USA, 2 patients in group 1 and 3 in the control group had a history of C. difficile infection


InterventionsL. rhamnosus GG 20 x 109 cfu/day or placebo within 24 hours of antibiotic commencement then for 14 days


OutcomesCDAD, AAD and AE


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Low risk“A randomization schedule was generated by the Section of Biostatistics and stratified on 3 parameters, including baseline daily bowel movement frequency (<1 vs >1), use of beta-lactams as initial antibiotic therapy, and age at entry (<65 vs >65 years).”

 

While the exact mechanism of randomization is not described we consider the involvement of the biostatistics department to be sufficient to assume a low risk of ‘material’ selection bias due to inadequate sequence generation

Allocation concealment (selection bias)Low risk“A pharmacist who at no time had direct contact with the patients or investigators dispensed active and placebo capsules according to the randomization schedule”

Blinding of participants and personnel (performance bias)
CDAD
Low riskQuotes: “Patients and investigators were blinded to the treatment.”

 

“Placebo capsules appeared identical to the active capsules...”

Blinding of participants and personnel (performance bias)
AE
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of participants and personnel (performance bias)
AAD
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of outcome assessment (detection bias)
CDAD
Low riskIt appears that CDAD was determined by following up with the participants’ primary care physicians and comparing hospital records of C. difficile positive patients which those enrolled in the trial. While it is not completely clear it seems as though the trial personnel were not those involved in assessing C. difficile but rather that those managing the patients ordered the tests themselves. Although this is unclear, this is a placebo controlled drug trial which is described as double blind. Based on our a priori determined criteria for the risk of bias for outcome assessor blinding this is sufficient to assess the risk of ‘material’ bias to be low here

Blinding of outcome assessment (detection bias)
AE
Low riskIt appears AE was reported by participants to study personnel all of whom were blinded

Blinding of outcome assessment (detection bias)
AAD
Low riskIt appears AAD was reported by blinded individuals

Incomplete outcome data (attrition bias)
CDAD
Low risk“Of the 302 patients who consented to participate, 34 failed to complete the study, and 1 patient enrolled but discontinued antibiotics after 1 dose, so was therefore determined to be ineligible. Thus, 267 patients completed the study.”

 

12% missing data. The placebo group had 16 participants withdrawn (Dropped out (n=9), Insufficient follow-up (n=7)) and the treatment group had 19 participants withdrawn (Dropped out (n=14), Insufficient follow-up (n=4), Discontinued antibiotic after 1 dose (n=1))

 

The numbers of missing data are grossly even between groups and not extreme. The reasons for withdrawal and dropout are not described.

 

“A chart review and a list of all patients with a positive C difficile toxin assay since July 1998 obtained from the Mayo Clinic microbiology laboratory revealed 5 study patients diagnosed as having and treated for C difficile colitis at our institution. Two of these patients were randomized to Lactobacillus GG, and 3 were randomized to placebo.”

The chart review displayed infrequent CDAD and seemingly same frequency in both groups. While the reasons for withdrawal and drop out were not clear, in light of the authors' negative findings we elected not to rate down here

Incomplete outcome data (attrition bias)
AE
Unclear risk“There was no difference in the proportion of patients experiencing nausea or abdominal cramping between the groups (P=.40 and P=.74, respectively). The patients receiving placebo tended to report gas or bloating more often than those receiving Lactobacillus GG (38.8% vs 28.0%), but this difference was not statistically significant (P=.06).”

 

Numbers of patients from each group experiencing the AE of nausea and abdominal cramping cannot be calculated from the presented data. The event rates for gas and bloating can be calculated and the event rates are frequent enough to most likely not be significantly influenced by the relatively low amount of missing data. However, not all event rates are clear and so it is difficult to assess the risk of attrition bias in this instance

Incomplete outcome data (attrition bias)
AAD
Unclear riskThe numbers of missing data are grossly even between groups and not extreme. The reasons for withdrawal and dropout are not described

Selective reporting (reporting bias)Low risk“The primary outcome was the proportion of patients experiencing diarrhea in the first 21 days after enrollment.”

 

“Two secondary outcomes were also assessed. The first was the proportion of patients who had either stool cultures or additional testing to determine the cause of diarrhea in the first 21 days after enrollment. These tests included fecal leukocyte counts, stool osmolality, and stool electrolytes. The second assessment was to determine the number of patients who were diagnosed as having AAD due to C difficile in the first 21 days or at any time after enrollment.”

 

Despite the clear declaration of outcomes in the ‘methods’ section the primary outcome was assessed with multiple subgroup analyses not discussed in ‘methods.’ Examples include subgroups based on type of antibiotic, differing definitions of diarrhea, duration of antibiotic treatment, severe diarrhea and length of hospitalization. Therefore the primary outcome of rate of diarrhea was “reported using measurements, analysis methods or subsets of the data (e.g. subscales) that were not pre-specified”. This classifies as a high risk of bias (Higgins 2011). This being said it is important to note that none of the subgroups resulted in significant findings either so this concern would be unlikely to bias the authors’ conclusion. Considering the authors’ conclusions, the direction of expected bias, and that these subgroups were not pertinent to our review, we consider the risk of a ‘material’ reporting bias that could influence our cumulative effect estimate in meta-analysis to be low 

Other biasLow risk“The treatment (n=133) and placebo (n=134) groups were similar in terms of their demographics and medical profiles at enrollment.” The study appears free of baseline imbalances.

 

“This study was supported in part by a grant from ConAgra Foods, Inc, Omaha, Neb.”

 

“Active capsules (CAG Functional Foods, Omaha, Neb)…” The study product is produced by a division of the sponsoring company (ConAgra). The sponsor is acknowledged and no one from the sponsoring agency was an author so based on our a priori defined criteria for funding bias we consider the risk of ‘material’ bias to be low

Wenus 2008

MethodsPlacebo controlled RCT


ParticipantsAdult population, NS, Norway, unclear if patients with recurrent C. difficile were included


InterventionsMixture of LGG, Lactobacillus acidophilus, and bifidobacterium 52.5 x 10^9 cfu/day or placebo for 14 days


OutcomesCDAD, AAD and C. difficile incidence


Notes


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskThe method of randomization was not described

Allocation concealment (selection bias)Unclear riskNo pertinent information provided and so it is unclear if allocation was successfully concealed

Blinding of participants and personnel (performance bias)
CDAD
Low risk“In this double-blind placebo controlled study…”

 

“Both products had a neutral taste…”

Blinding of participants and personnel (performance bias)
C. difficile incidence
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of participants and personnel (performance bias)
AAD
Low riskSee above: Blinding of participants and personnel (performance bias) CDAD

Blinding of outcome assessment (detection bias)
CDAD
Low riskThere is no mention of blinding of the cytotoxin assay personnel although this is a placebo controlled drug trial so in accordance with our a priori defined RoB criteria we will consider the risk of bias to be low here

Blinding of outcome assessment (detection bias)
C. difficile incidence
Low riskSee above: Blinding of outcome assessment (detection bias) CDAD

Blinding of outcome assessment (detection bias)
AAD
Low riskDiarrhea assessed by participants who were blinded

Incomplete outcome data (attrition bias)
CDAD
High risk“The remaining 87 intention-to-treat patients were randomized to probiotic (n = 46) or placebo (n = 41) treatment. Groups were well balanced at study entry (Table 1). During the study there were 12 withdrawals/drop-outs in each treatment group (Figure 1). The remaining 34 and 29 patients in the active and placebo group, respectively, completed the study according to the protocol. The withdrawal/drop-out group did not differ from the per-protocol group with respect to age, sex, usual number of stools/day and previous experiences of AAD (data not shown).

 

“Stool samples were collected twice during the study period.”

 

“Owing to low patient compliance, only 55 stool samples were examined. In the non-AAD/probiotic group one sample was positive for C. difficile culture, and another sample was positive for C. difficile toxin A. In the AAD/placebo group one sample was positive for C. difficile culture”

 

“Our study was based on per-protocol analysis. Intention-to-treat analysis could not be obtained as end point data was lacking for several patients owing to withdrawal or drop-out.”

 

Comment: There are missing outcome data on 28% of randomized participants. Additionally it appears that of the remaining 63 participants there should have been 126 stool samples for C. difficile analysis. Only 55 were analysed. These concerns coupled with an extremely low C. difficile incidence event rate lead us to consider the risk of ‘material’ attrition bias to be high

Incomplete outcome data (attrition bias)
C. difficile incidence
High riskSee above: Incomplete outcome data (attrition bias) CDAD

Incomplete outcome data (attrition bias)
AAD
High riskSee above: Incomplete outcome data (attrition bias) CDAD

Selective reporting (reporting bias)Low riskNo protocol for this study was identified. All outcomes listed in the ‘methods’ section were analysed in the ‘results’ section

Other biasLow riskGroups apparently free of baseline imbalances. The investigated product is produced by the sponsor of this trial (Biola: TINE BA, Oslo, Norway). No author was associated with the sponsoring company

 
Characteristics of excluded studies [ordered by study ID]

StudyReason for exclusion

Agarwal 2003C. difficile or CDAD not measured

Allen 2012Not an RCT

Anukam 2006C. difficile or CDAD not measured

Armuzzi 2001C. difficile or CDAD not measured

Avadhani 2011Not an RCT

Basu 2007C. difficile or CDAD not measured

Bekar 2011C. difficile or CDAD not measured

Bellomo 1980C. difficile or CDAD not measured

Benhamou 1999C. difficile or CDAD not measured

Beniwal 2003C. difficile or CDAD not measured

Berni 2011Not an RCT

Black 1991C. difficile or CDAD not measured

Bleichner 1997C. difficile or CDAD not measured

Brunser 2006C. difficile or CDAD not measured

Butler 2012Not an RCT

Chapman 2011Not an RCT

Chen 2011Not an RCT

Cimperman 2011C. difficile or CDAD not measured

Clements 1981C. difficile or CDAD not measured

Contardi 1991C. difficile or CDAD not measured

Conway 2007C. difficile or CDAD not measured

Correa 2005C. difficile or CDAD not measured

Cremonini 2002C. difficile or CDAD not measured

de Bortoli 2007C. difficile or CDAD not measured

de Vrese 2011C. difficile or CDAD not measured

Elmer 1999Patients had active diarrhea or CDAD

Erdeve 2004C. difficile or CDAD not measured

Felley 2001C. difficile or CDAD not measured

Forestier 2008C. difficile or CDAD not measured

Francavilla 2008C. difficile or CDAD not measured

Goldman 2006C. difficile or CDAD not measured

Gotteland 2005C. difficile or CDAD not measured

Gotz 1979C. difficile or CDAD not measured

Guandalini 2000C. difficile or CDAD not measured

Hafeez 2002C. difficile or CDAD not measured

Hatakka 2001C. difficile or CDAD not measured

Heimburger 1994C. difficile or CDAD not measured

Hotz 1990C. difficile or CDAD not measured

Hurduc 2009C. difficile or CDAD not measured

Jacobi 2011Not an RCT

Jirapinyo 2002C. difficile or CDAD not measured

Kato 2004C. difficile or CDAD not measured

Kollaritsch 1993C. difficile or CDAD not measured

Kruis 2012C. difficile or CDAD not measured

La Rosa 2003C. difficile or CDAD not measured

Lawrence 2005Patients had active diarrhea or CDAD

Lei 2006C. difficile or CDAD not measured

Lionetti 2006C. difficile or CDAD not measured

Madden 2005C. difficile or CDAD not measured

Madeo 1999C. difficile or CDAD not measured

Marcone 2008C. difficile or CDAD not measured

Marshall 2008Not an RCT

Martinez 2009C. difficile or CDAD not measured

McFarland 1994aPatients had active diarrhea or CDAD

Merenstein 2009C. difficile or CDAD not measured

Mihatsch 2010C. difficile or CDAD not measured

Mohan 2008C. difficile or CDAD not measured

Myllyluoma 2005C. difficile or CDAD not measured

Myllyluoma 2007C. difficile or CDAD not measured

Nista 2004C. difficile or CDAD not measured

Oleinichenko 1999C. difficile or CDAD not measured

Ozdil 2011C. difficile or CDAD not measured

Park 2007C. difficile or CDAD not measured

Pereg 2005C. difficile or CDAD not measured

Pirotta 2004C. difficile or CDAD not measured

Plewinska 2006C. difficile or CDAD not measured

Pochapin 2000Patients had active diarrhea or CDAD

Potts 1996C. difficile or CDAD not measured

Pushkarev 2005C. difficile or CDAD not measured

Ranasinghe 2007C. difficile or CDAD not measured

Rayes 2002aC. difficile or CDAD not measured

Rayes 2002bC. difficile or CDAD not measured

Rayes 2002cC. difficile or CDAD not measured

Reddy 2007C. difficile or CDAD not measured

Robertson 2000Not an RCT

Sahagún-Flores 2007C. difficile or CDAD not measured

Schrezenmeir 2002C. difficile or CDAD not measured

Schrezenmeir 2004C. difficile or CDAD not measured

Sepp 2011Not an RCT

Souza 2012C. difficile or CDAD not measured

Stein 2007C. difficile or CDAD not measured

Stockenhuber 2008Not an RCT

Tankanow 1990C. difficile or CDAD not measured

Tursi 2004C. difficile or CDAD not measured

Vandenplas 2011C. difficile or CDAD not measured

Wilhelm 2011Not an RCT

Witsell 1995C. difficile or CDAD not measured

Woo 2008Not an RCT

Wullt 2007Patients had active diarrhea or CDAD

Yoon 2011C. difficile or CDAD not measured

Yost 1985C. difficile or CDAD not measured

Ziemniak 2006C. difficile or CDAD not measured

 
Comparison 1. C. difficile associated diarrhea

Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size

 1 Incidence CDAD: complete case234213Risk Ratio (M-H, Random, 95% CI)0.36 [0.26, 0.51]

 2 Incidence CDAD: complete case - fixed effects234213Risk Ratio (M-H, Fixed, 95% CI)0.36 [0.26, 0.49]

 3 Incidence CDAD Sensitivity (1.5:1)234674Risk Ratio (M-H, Random, 95% CI)0.38 [0.27, 0.53]

 4 Incidence CDAD Sensitivity (2:1)234674Risk Ratio (M-H, Random, 95% CI)0.41 [0.30, 0.57]

 5 Incidence CDAD Sensitivity (3:1)234674Risk Ratio (M-H, Random, 95% CI)0.47 [0.33, 0.68]

 6 Incidence CDAD Sensitivity (5:1)234674Risk Ratio (M-H, Random, 95% CI)0.57 [0.38, 0.85]

 7 Incidence CDAD: Subgroup: Inpatient versus outpatient populations214026Risk Ratio (M-H, Random, 95% CI)0.36 [0.26, 0.52]

    7.1 Inpatient
142359Risk Ratio (M-H, Random, 95% CI)0.35 [0.24, 0.52]

    7.2 Outpatient
2462Risk Ratio (M-H, Random, 95% CI)0.31 [0.01, 7.47]

    7.3 Mixed
51205Risk Ratio (M-H, Random, 95% CI)0.43 [0.20, 0.94]

 8 Incidence CDAD: Subgroup: Species: all224156Risk Ratio (M-H, Random, 95% CI)0.36 [0.26, 0.51]

    8.1 Lactobacillus GG
51131Risk Ratio (M-H, Random, 95% CI)0.63 [0.30, 1.33]

    8.2 S. boulardii
71507Risk Ratio (M-H, Random, 95% CI)0.47 [0.24, 0.94]

    8.3 L. acidophilus + L. casei
3781Risk Ratio (M-H, Random, 95% CI)0.21 [0.11, 0.42]

    8.4 L. acidophilus + B. bifidum
1138Risk Ratio (M-H, Random, 95% CI)0.40 [0.08, 1.99]

    8.5 L. acidophilus
140Risk Ratio (M-H, Random, 95% CI)0.25 [0.01, 5.79]

    8.6 L. acidophilus + L. bulgaricus + B. bifidum + S. thermophilus
1100Risk Ratio (M-H, Random, 95% CI)0.28 [0.11, 0.67]

    8.7 B. breve + B. Longum + B. infantis + L. acidophilus + L. plantarum + L. paracasei + L. bulgaricus + S. thermophilus
1124Risk Ratio (M-H, Random, 95% CI)0.0 [0.0, 0.0]

    8.8 L. casei + L. bulgaris + S. thermophilus
1109Risk Ratio (M-H, Random, 95% CI)0.05 [0.00, 0.84]

    8.9 L. plantarum
1163Risk Ratio (M-H, Random, 95% CI)3.11 [0.13, 75.26]

    8.10 Lactobacillus GG + L. acidophilus + B. animalis
163Risk Ratio (M-H, Random, 95% CI)0.29 [0.01, 6.76]

 9 Incidence CDAD: Subgroup: Species: LGG versus SB122638Risk Ratio (M-H, Random, 95% CI)0.54 [0.33, 0.90]

    9.1 Lactobacillus GG
51131Risk Ratio (M-H, Random, 95% CI)0.63 [0.30, 1.33]

    9.2 S. boulardii
71507Risk Ratio (M-H, Random, 95% CI)0.47 [0.24, 0.94]

 10 Incidence CDAD: Subgroup: Species: LGG versus LA + LC81912Risk Ratio (M-H, Random, 95% CI)0.35 [0.21, 0.57]

    10.1 Lactobacillus GG
51131Risk Ratio (M-H, Random, 95% CI)0.63 [0.30, 1.33]

    10.2 L. acidophilus + L. casei
3781Risk Ratio (M-H, Random, 95% CI)0.21 [0.11, 0.42]

 11 Incidence CDAD: Subgroup: Risk of Bias234280Risk Ratio (M-H, Random, 95% CI)0.36 [0.26, 0.51]

    11.1 Low risk of bias
71308Risk Ratio (M-H, Random, 95% CI)0.27 [0.16, 0.46]

    11.2 High or unclear risk of bias
162972Risk Ratio (M-H, Random, 95% CI)0.45 [0.28, 0.72]

 12 Incidence CDAD: Subgroup: Adult versus child224156Risk Ratio (M-H, Random, 95% CI)0.36 [0.26, 0.51]

    12.1 Adult studies
193551Risk Ratio (M-H, Random, 95% CI)0.36 [0.24, 0.52]

    12.2 Pediatric studies
3605Risk Ratio (M-H, Random, 95% CI)0.40 [0.17, 0.96]

 
Comparison 2. Adverse events

Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size

 1 Adverse Events: complete case263964Risk Ratio (M-H, Random, 95% CI)0.80 [0.68, 0.95]

 2 Adverse Events: Subgroup: Risk of Bias264031Risk Ratio (M-H, Random, 95% CI)0.80 [0.68, 0.95]

    2.1 Low Risk of Bias
122120Risk Ratio (M-H, Random, 95% CI)0.84 [0.72, 0.98]

    2.2 High/Unclear risk of bias
141911Risk Ratio (M-H, Random, 95% CI)0.54 [0.29, 0.99]

 3 AE Sensitivity 1.5:1264468Risk Ratio (M-H, Random, 95% CI)0.82 [0.69, 0.99]

 4 AE Sensitivity 2:1264468Risk Ratio (M-H, Random, 95% CI)0.85 [0.70, 1.03]

 5 AE Sensitivity 3:1264468Risk Ratio (M-H, Random, 95% CI)0.88 [0.70, 1.10]

 6 AE Sensitivity 5:1264468Risk Ratio (M-H, Random, 95% CI)0.93 [0.72, 1.21]

 
Comparison 3. Incidence of Clostridium difficile infection

Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size

 1 Incidence of infection: complete case13961Risk Ratio (M-H, Random, 95% CI)0.89 [0.64, 1.24]

 2 Incidence of infection: Subgroup: Risk of Bias13961Risk Ratio (M-H, Random, 95% CI)0.89 [0.64, 1.24]

    2.1 Low Risk of Bias
3130Risk Ratio (M-H, Random, 95% CI)0.83 [0.31, 2.20]

    2.2 High or Unclear Risk of Bias
10831Risk Ratio (M-H, Random, 95% CI)0.90 [0.63, 1.28]

 
Comparison 4. Length of hospital stay

Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size

 1 Length of Hospital Stay: complete case3422Mean Difference (IV, Random, 95% CI)-0.32 [-3.21, 2.57]

 
Comparison 5. Antibiotic associated diarrhea

Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size

 1 Incidence AAD: complete case254097Risk Ratio (M-H, Random, 95% CI)0.60 [0.49, 0.72]

 2 Incidence AAD: Subgroup: Risk of Bias254097Risk Ratio (M-H, Random, 95% CI)0.60 [0.49, 0.72]

    2.1 Low risk of bias
132154Risk Ratio (M-H, Random, 95% CI)0.58 [0.46, 0.73]

    2.2 High or Unclear risk of bias
121943Risk Ratio (M-H, Random, 95% CI)0.62 [0.44, 0.88]

 3 Incidence AAD: sensitivity (1.5:1)254581Risk Ratio (M-H, Random, 95% CI)0.69 [0.58, 0.82]

 4 Incidence AAD: sensitivity (2:1)254581Risk Ratio (M-H, Random, 95% CI)0.73 [0.60, 0.88]

 5 Incidence AAD: sensitivity (3:1)254581Risk Ratio (M-H, Random, 95% CI)0.80 [0.64, 0.99]

 6 Incidence AAD: sensitivity (5:1)254581Risk Ratio (M-H, Random, 95% CI)0.90 [0.69, 1.18]

 7 Patient population213853Risk Ratio (M-H, Random, 95% CI)0.62 [0.50, 0.76]

    7.1 Inpatient
132138Risk Ratio (M-H, Random, 95% CI)0.66 [0.49, 0.88]

    7.2 Outpatient
3510Risk Ratio (M-H, Random, 95% CI)0.51 [0.30, 0.87]

    7.3 Mixed
51205Risk Ratio (M-H, Random, 95% CI)0.55 [0.35, 0.86]

 8 Species: all254097Risk Ratio (M-H, Random, 95% CI)0.60 [0.49, 0.72]

    8.1 Lactobacillus GG
4942Risk Ratio (M-H, Random, 95% CI)0.75 [0.39, 1.43]

    8.2 S. boulardi
91642Risk Ratio (M-H, Random, 95% CI)0.56 [0.39, 0.80]

    8.3 L. acidophilus + L. casei
3781Risk Ratio (M-H, Random, 95% CI)0.59 [0.42, 0.81]

    8.4 Clostridium butyricum
254Risk Ratio (M-H, Random, 95% CI)0.29 [0.06, 1.34]

    8.5 L. acidophilus + B. bifidum
1138Risk Ratio (M-H, Random, 95% CI)0.83 [0.51, 1.36]

    8.6 L. acidophilus
139Risk Ratio (M-H, Random, 95% CI)0.46 [0.16, 1.38]

    8.7 B. breve + B. longum + B. infantis + L. acidophilus + L. plantarum
1124Risk Ratio (M-H, Random, 95% CI)0.4 [0.08, 1.98]

    8.8 L. casei + L. bulgaris + S. thermophilus
1113Risk Ratio (M-H, Random, 95% CI)0.36 [0.17, 0.79]

    8.9 L. plantarum
1163Risk Ratio (M-H, Random, 95% CI)1.25 [0.40, 3.92]

    8.10 Lactobacillus GG + L. acidophilus + B. animalis
163Risk Ratio (M-H, Random, 95% CI)0.21 [0.05, 0.93]

    8.11 B. bifidum + B. lactis + B. longum + E. faecium + L. acidophilus + L. paracasei + L. plantarum + L. rhamnosus + L. sativarius
138Risk Ratio (M-H, Random, 95% CI)0.6 [0.35, 1.02]

 9 Species: LGG versus SB132584Risk Ratio (M-H, Random, 95% CI)0.62 [0.45, 0.86]

    9.1 LGG
4942Risk Ratio (M-H, Random, 95% CI)0.75 [0.39, 1.43]

    9.2 SB
91642Risk Ratio (M-H, Random, 95% CI)0.56 [0.39, 0.80]

 10 Species: LGG versus LA + LC71723Risk Ratio (M-H, Random, 95% CI)0.65 [0.47, 0.91]

    10.1 LGG
4942Risk Ratio (M-H, Random, 95% CI)0.75 [0.39, 1.43]

    10.2 LA + LC
3781Risk Ratio (M-H, Random, 95% CI)0.59 [0.42, 0.81]

 11 Adult versus child223974Risk Ratio (M-H, Random, 95% CI)0.59 [0.49, 0.71]

    11.1 Adult
193369Risk Ratio (M-H, Random, 95% CI)0.63 [0.51, 0.76]

    11.2 Child
3605Risk Ratio (M-H, Random, 95% CI)0.37 [0.23, 0.60]

 
Summary of findings for the main comparison. Probiotics for the prevention of Clostridium difficile associated diarrhea

Probiotics for the prevention of Clostridium difficile associated diarrhea

Patient or population: adults and children exposed to antibiotics
Settings: inpatient and outpatient
Intervention: probiotics

OutcomesIllustrative comparative risks* (95% CI)Relative effect
(95% CI)
No of Participants
(studies)
Quality of the evidence
(GRADE)
Comments

Assumed riskCorresponding risk

ControlProbiotics

Clostridium difficile associated diarrhea
diarrhea as defined by authors + cytotoxin and culture or both
Study populationRR 0.36
(0.26 to 0.51)
4213
(23 studies)
⊕⊕⊕⊝
moderate1,2,3,4,5,6

55 per 100020 per 1000
(14 to 28)

Median

35 per 100013 per 1000
(9 to 18)

Adverse events
as defined or described by authors
Study populationRR 0.80
(0.68 to 0.95)
3964
(26 studies)
⊕⊕⊕⊝
moderate7,8,9,10,11

187 per 1000150 per 1000
(127 to 178)

Median

69 per 100055 per 1000
(47 to 66)

Clostridium difficile infection
cytotoxin and/or culture
Study populationRR 0.89
(0.64 to 1.24)
961
(13 studies)
⊕⊕⊕⊝
moderate12,13,14,15,16

127 per 1000113 per 1000
(82 to 158)

Median

105 per 100093 per 1000
(67 to 130)

Length of hospital stay
days spent in hospital
The mean length of hospital stay in the control groups was
10.3 days
The mean length of hospital stay in the intervention groups was
0.32 lower
(3.21 lower to 2.57 higher)
422
(3 studies)
⊕⊕⊝⊝
low17,18,19,20,21

Antibiotic associated diarrhea
as defined by study authors
Study populationRR 0.60
(0.49 to 0.72)
4097
(25 studies)
⊕⊕⊝⊝
low22,23,24,25,26

209 per 1000125 per 1000
(102 to 151)

Median

220 per 1000132 per 1000
(108 to 158)

*The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).
CI: Confidence interval; RR: Risk ratio;

GRADE Working Group grades of evidence
High quality: Further research is very unlikely to change our confidence in the estimate of effect.
Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
Very low quality: We are very uncertain about the estimate.

 1 Low risk of bias studies (7/23) demonstrated a slightly more favorable protective effect than studies at high or unclear risk of bias (16/23). A test for subgroup differences did not find a statistically significant difference based on risk of bias (P = 0.16).
2 16 of 23 trials had missing CDAD data ranging from 5 to 45%. A sensitivity analysis using plausible and worst-plausible ratios of event rates in those with missing data in comparison to those successfully followed, demonstrated the CDAD results were robust to all assumptions (worst-plausible analysis: RR 0.57; 95% CI 0.38 to 0.85).
3 Effect sizes are consistent across all 23 studies (I2 = 0%; P=0.76).
4 Outcome assessed in all 23 studies is the outcome of interest for our health question.
5 Using standard alpha (0.05) and beta (0.20) values, for a RRR of 30% the optimal information size (n = 8218) was more than the total sample size (n = 4213). Additionally, overall events were very low (154) and as a result we rated down for imprecision.
6 Funnel plot inspection as well as Harbord's linear regression test (P = 0.11) are not suggestive of publication bias or other small study effects.
7 Test for risk of bias subgroup differences was not statistically significant (P = 0.16). However, only 26 of 31 trials reported on adverse events, an outcome that would presumably be documented in all probiotics trials. We therefore rated down for selective reporting bias.
8 Minimal heterogeneity between trials (I2 = 37%; P = 0.06).
9 Outcome assessed in these 26 studies is the outcome of interest for our health question.
10 Using standard alpha (0.05) and beta (0.20) values, we calculated the optimal information size based on a relative risk decrease of 30%. The OIS (n = 4044) was greater than the total sample size (n = 3964). However, given that the number of overall events was high (events = 639) we did not rate down for imprecision.
11 Funnel plot inspection and Harbord's linear regression test found no visual or statistical evidence of small study effects (P = 0.24).
12 Three studies were rated as having a low risk of bias. Ten were rated as having an unclear or high risk of bias. A test for risk of bias subgroup differences was not statistically significant (P = 0.88).
13 Effect sizes are consistent across the 13 studies reporting on C. difficile infection (I2 = 0%; P = 0.84).
14 Outcome assessed in all 13 studies is the outcome of interest for our health question.
15 Total event rate of all 13 studies is very low (122) and the 95% confidence interval includes both no effect and a substantial effect size. We therefore rated down for imprecision.
16 Funnel plot inspection as well as Harbord's linear regression test revealed no visual or statistical evidence of small study effects (P = 0.56).
17 We suspect selective outcome reporting bias as only 3 of 31 identified trials, most of which occurred in hospitals, reported on length of hospital stay - a presumably patient and hospital important outcome. Of the three studies reporting on length of stay, one had an unclear risk of bias and two were rated as having a low risk of bias.
18 Minimal heterogeneity between studies (I2 = 20%; P = 0.29).
19 Outcome assessed is the outcome of interest for our health question.
20 Using an alpha of 0.05 and beta of 0.20, the optimal information size to detect a two day difference in hospital stay (n = 800) was larger than the pooled sample size (n = 422). We therefore rated down for imprecision.
21 With only 3 trials reporting on length of stay, publication bias was not assessed.
22 A test for subgroup differences between low risk of bias studies (n = 13) versus high risk or unclear risk of bias studies (n = 12) was not statistically significant (P = 0.74). Eleven of 25 trials had missing AAD data ranging from 4% to 43%.  A sensitivity analysis using plausible and worst-plausible ratios of event rates in those with missing data in comparison to those successfully followed, demonstrated the AAD results were not robust to all assumptions (worst-plausible, RR 0.90; 95% CI 0.69 to 1.18). We therefore rated down for risk of bias associated with missing participant data.
23 There was statistically significant heterogeneity across the 25 studies (I2 = 36%. P = 0.04). We explored potential reasons for this observed heterogeneity using a priori defined subgroup analyses revealing that age (i.e. adult versus pediatric subgroup) may explain the observed heterogeneity (test of interaction: P = 0.05). Using 11 published criteria to evaluate the credibility of this subgroup, our subgroup analysis on age represents a credible subgroup effect. We therefore did not rate down for inconsistency (Sun 2010).
24 Outcome assessed in all 25 studies is the outcome of interest for our health question.
25 Using an alpha of 0.05 and beta of 0.20, for a RRR of 30% the optimal information size (n = 1094) was less than the total sample size (n = 4097).
26 While the funnel plot may suggest asymmetry, Harbord's linear regression test was negative for publication (or other small study effect) bias (P = 0.31). However our inclusion criteria (trials reporting on C. difficile) likely introduced a selection bias and we again rated down our confidence in the estimate of effect.