An estimated 2.6 billion people or 40% of the world's population lack access to improved facilities for the disposal of human excreta, such as a latrine connected to a piped sewer system, or a composting toilet (United Nations 2005). In developing regions, where people are most vulnerable to infection and disease, only one in two people is covered by improved sanitation. But even these alarming figures obscure the severity of the problem in certain areas. In sub-Saharan Africa, South Asia, and Eastern Asia, coverage is just 37%, 38%, and 45%, respectively (United Nations 2005). In rural areas, coverage is 39% worldwide, and, if current trends continue, more than half of the rural population will still be without sanitation coverage in 2015 (United Nations 2005). In Africa and East Asia, it is five to seven times more likely that urban dwellers will have improved sanitation than their rural counterparts (WHO/UNICEF 2006). However, due to migration into cities, urban sanitation also represents a continuing challenge. Despite an increase of almost 40% in the number of people served with improved sanitation between 1990 and 2004, current projections suggest that the raw number of urban dwellers without access to improved sanitation will actually increase by 50% from 1990 to 2015 (WHO/UNICEF 2006).
The shortfall in sanitation coverage is not the result of a failure to recognize the need or declare goals at the highest international level. The 1977 Mar del Plata Declaration by the United Nations expressed the goal of providing safe water and sanitation for all by 1990, launching the Water and Sanitation Decade (1981 to 1990). In 1990, the United Nations renewed the call and extended the deadline to the end of the century. While sanitation was first omitted from the United Nations Millennium Development Goals (MDGs), it was added to the water target at the Johannesburg-based World Summit on Sustainable Development in 2002. Target 10 of Goal 7 is less ambitious than its predecessor objectives, seeking only to reduce by half the portion of the population without access to "basic" sanitation. Even so, the evidence suggests that current efforts will fall far short of even this scaled down target; in sub-Saharan Africa, current efforts will actually result in an increase in the number served by 91 million (WHO/UNICEF 2005; UNDP 2007). Of course, even if the MDGs target could be met, it would still leave well more than one billion without such access. In a further effort to attract attention to this deficit and additional priority to the sector, the United Nations General Assembly declared 2008 as the International Year of Sanitation (United Nations 2006).
Definitions of sanitation
Despite the apparent agreement about the need for sanitation and the value of monitoring progress, there is no clear consensus over what precisely should be promoted. In its broadest sense, sanitation deals not only with the collection, storage, treatment, disposal, reuse, or recycling of human excreta (faeces and urine), but also the drainage, disposal, recycling and re-use of wastewater and storm water (sullage), and household, industrial, and hazardous solid wastes. The MDGs target, which is expressed in terms of "basic sanitation", followed this broader approach and also included concepts of affordability, cultural acceptability, and environmental sustainability (United Nations 2002). The United Nations Millennium Task Force on Water and Sanitation attempted to consolidate these notions, defining 'basic sanitation" as "the lowest-cost option for securing sustainable access to safe, hygienic, and convenient facilities and services for excreta and sullage disposal that provide privacy and dignity, while at the same time ensuring a clean and healthful living environment both at home and in the neighbourhood of users" (Millennium Proj 2005). The MDGs definition is context specific. In dispersed, low-income, rural areas, it may include a simple pit latrine, while in congested urban slums with reliable water service, household-based solutions would be deemed inadequate and low-cost sewerage systems would be necessary to ensure proper collection, treatment, and disposal or re-use of excreta and household wastewater (Millennium Proj 2005).
At the end of the Water and Sanitation Decade, the World Health Organization (WHO) and United Nations Children's Fund (UNICEF) agreed to combine their experience and resources in a Joint Monitoring Programme for Water Supply and Sanitation (JMP). Before 2000, the JMP used data supplied by governments, yielding results that were inconsistent and unreliable. Since 2000, the JMP has used national representative household surveys such as Multi-Indicator Cluster Surveys, the Living Standards Measurement Studies, Demographic and Health Surveys, and census data to publish Global Water Supply and Sanitation Assessments in 1991, 1993, 1996, and 2000. While definitions used by the JMP have evolved over the course of these assessments, in 2000 the JMP defined the terms "improved sanitation" and "unimproved sanitation" in terms of the facilities for the disposal of human excreta. Improved sanitation includes a private flush or pour-flush toilet or latrine connected to a piped sewer system or septic system, simple pit latrine with slab, ventilated improved pit latrine, or composting toilet. Unimproved sanitation includes any other flush or pour-flush latrine, open pit latrine, bucket latrines, hanging latrine, any public or shared facility, or open defecation (WHO/UNICEF 2002).
Neither set of definitions is strictly health-based. The MDGs definition addresses not only safety and hygiene, but also convenience, cost, privacy, and dignity. It emphasizes household and community impact, sustainability, and actual use by the covered population. While the JMP classification is intended to reflect the health risk associated with safe excreta disposal, the distinction between improved and unimproved facilities is based mainly on observable criteria developed by the JMP to facilitate surveys of coverage and promote the upgrading of facilities. The differences between these definitions are not merely academic; funding and other resources are largely directed at increasing coverage reported by the JMP and meeting the MDGs targets (UNDP 2007). At a minimum, however, both definitions agree that sanitation must include the disposal of human excreta, a criterion that is founded in health. For this reason, this review focuses on interventions to improve excreta disposal facilities.
Diarrhoeal disease, disease agents, and pathways
Diarrhoeal diseases kill an estimated 1.8 million people each year (WHO 2005). Among infectious diseases, diarrhoea ranks as the third leading cause of both mortality and morbidity (after respiratory infections and HIV/AIDS), placing it above tuberculosis and malaria. Young children are especially vulnerable, bearing 68% of the total burden of diarrhoeal disease (Bartram 2003). Among children younger than five years, diarrhoea accounts for 17% of all deaths (United Nations 2005). For those infected with the human immunodeficiency virus or who have developed acquired immunodeficiency syndrome (AIDS), diarrhoea can be prolonged, severe, and life-threatening (Hayes 2003).
Diarrhoea is characterized by stools of decreased consistency and increased number. The clinical symptoms and course of the disease vary greatly with age, nutritional and immune status, and the pathogen. Most cases resolve within a week, though a small percentage continue for two weeks or more and are characterized as 'persistent diarrhoea'. Dysentery is a diarrhoeal disease defined by the presence of blood in the liquid stools (Blaser 1995). Though epidemic diarrhoea such as cholera and shigellosis (bacillary dysentery) are well-known risks, particularly in emergency settings, their global health significance is small compared to endemic diarrhoea (Hunter 1997).
The immediate threat from diarrhoea is dehydration and a loss of fluids and electrolytes. Thus, the widespread promotion of oral rehydration therapy has significantly reduced the case-fatality rate associated with the disease. Such improvements in case management, however, have not reduced morbidity, which is estimated at four billion cases annually (Kosek 2003). And since diarrhoeal diseases inhibit normal ingestion of foods and adsorption of nutrients, continued high morbidity is an important cause of malnutrition, leading to impaired physical growth and cognitive function (Guerrant 1999), reduced resistance to infection (Baqui 1993), and potentially long-term gastrointestinal disorders (Schneider 1978). With continued high attack rates, diarrhoeal disease is also an enormous economic burden, resulting in significant direct costs to the health sector and patients for treatment as well as in lost time at school, work, and other productive activities (Mulligan 2005).
The infectious agents associated with diarrhoeal disease are transmitted chiefly through the faecal-oral route (Byers 2001). A wide variety of bacterial, viral, and protozoan pathogens excreted in the faeces of humans and animals are known to cause diarrhoea. Among the most important of these are Escherichia coli, Salmonella spp., Shigella spp., Campylobacter jejuni, Vibrio cholerae, rotavirus, norovirus, Giardia lamblia, Cryptosporidium spp., and Entamoeba histolytica (Leclerc 2002). The importance of individual pathogens varies between settings, seasons, and conditions. Although diarrhoea is also associated with the ingestion of metals, nitrates, organics, and other chemicals, the burden of disease arising from such exposure is small relative to infectious diarrhoea (WHO 2002).
These diarrhoegenic agents may be transmitted through the ingestion of contaminated food, water, or other beverages, by person-to-person contact, and by direct or indirect contact with infected faeces. Because of this variety of pathways, environmental interventions for the prevention of diarrhoeal disease typically include steps to improve the proper disposal of human faeces (sanitation), improve water quality (Clasen 2006), improve water quantity and access, and promote hand washing and other hygiene practices (Ejemot 2008).
Excreta disposal and diarrhoea
While the biologic association between diarrhoea and exposure to human faeces is well established, there is comparatively little rigorous epidemiologic evidence of the effectiveness of sanitation interventions to prevent disease. A previous Cochrane Review examined "environmental sanitary interventions", but it was limited to interventions to prevent active trachoma and, accordingly, extended only to excreta disposal interventions undertaken as fly control measures (Rabiu 2005). Moreover, the review identified only a single study of an excreta disposal intervention (Emerson 2004), and in that study the intervention reduced eye-fly contact but had not statistically significant impact on the prevalence of active trachoma.
With respect to diarrhoea, there are three previous reviews of excreta disposal interventions (Esrey 1985; Esrey 1991; Fewtrell 2005). Esrey and colleagues identified 10 studies of improvements in excreta disposal with a median reduction in diarrhoea of 22% (range of 0% to 48%) (Esrey 1985). A subsequent review of "sanitation" interventions reported a median reduction of 30% from 11 studies (36% from five studies the investigators deemed rigorous) (Esrey 1991). Esrey and colleagues based their conclusions chiefly on observational studies. In addition to the confounding and bias inherent in such studies, Esrey and others have pointed out significant and widespread methodological problems with these studies (Blum 1983; Esrey 1986). Although these previous reviews were helpful in identifying the broad questions and suggesting answers, they did not employ the more rigorous methodologies and statistical methods, including meta-analysis, of a systematic review (Egger 2001). In terms of coverage, for example, neither review involved a comprehensive search strategy. Accordingly, the conclusions with respect to sanitation are based on a limited number of studies. The reviews were also limited to studies in the English language. With respect to statistical methods, the simple use of the median fails to take into account the size of the study and the variance observed in the results (Deeks 2001). Also, Esrey and colleagues ignored the clustering effect of introducing interventions at the community level rather than individual level. Moreover, they did not distinguish between the various case definitions (Moy 1991) and measures of diarrhoea morbidity (Pickering 1987; Morris 1996). Also, while Esrey attempted to incorporate quality criteria in the reviews, there was no independent assessment of study quality or, for that matter, whether identified studies met the inclusion criteria.
An update of Esrey's review of environmental interventions to prevent diarrhoea addresses some of these methodological shortcomings. Fewtrell and colleagues conducted a more formal systematic review and meta-analysis of environmental interventions against diarrhoea (Fewtrell 2005). They identified just four such studies of improved sanitation, only two of which provided data that they could use in a meta-analysis. Fewtrell and colleagues reported the interventions to be protective, with a pooled relative risk of 0.68 (95% confidence interval 0.53 to 0.87) − a 32% reduction in diarrhoea that would appear consistent with Esrey's findings. In addition to being based on just two studies, however, there are other reasons to question the evidentiary weight of this estimate. First, the review was limited to published studies and did not include a search of Chinese databases. Second, only one of the two studies had endemic diarrhoea as its outcome (Daniels 1990); the other study (Azurin 1974) based its findings on cholera, a source of epidemic diarrhoea against which environmental interventions tend to be more effective than can be expected for general diarrhoea (Gundry 2004). Finally, the study conducted by Daniels and colleagues followed an observational design, even though Emerson and colleagues (Emerson 2004) have demonstrated that a health impact (trachoma) from latrines can be investigated using the more rigorous randomized, controlled trial design.
Beyond the paucity of rigorous epidemiologic evidence in support of sanitation interventions, there is relatively little evidence of the acceptability, scalability, and sustainability of steps to improve excreta disposal, especially in rural settings where coverage is lowest (Jenkins 2005). This limited evidence may be contributing to the comparatively slow progress in achieving the sanitation target under the MDGs.
To assess the effectiveness of interventions to improve human excreta disposal for preventing diarrhoeal disease.
Criteria for considering studies for this review
Types of studies
Randomized and quasi-randomized controlled trials. The unit of randomization may include individuals, families, households, communities, or other clusters.
Types of participants
Children and adults.
Types of interventions
Interventions aimed at disposing of human excreta in a manner designed to reduce the direct or indirect human contact. This includes any steps to remove or contain faeces, such as simple pit latrines, ventilated improved pit latrines, bucket latrines, hanging toilets, water sealed pour-flush toilets (whether or not connected to a vault, septic tank, or sewer), and composting toilets, and should be contrasted with open defecation.
We will include interventions that combine improvements in excreta disposal with other environmental interventions such as improvements in water quantity or access, water quality or hygiene practices, and will use subgroup analysis to explore the impact of such additional components.
Study participants who are following their usual practices with respect to excreta disposal rather than the prescribed intervention, or who have received a different type of intervention.
Types of outcome measures
Diarrhoea episodes among individuals, whether or not confirmed by microbiological examination. The WHO's definition of diarrhoea is three or more loose or fluid stools (that take the shape of the container) in a 24-hour period (WHO 1993). We will define diarrhoea and an episode in accordance with the case definitions used in each trial. We will exclude trials that had no clinical outcomes; for example, trials that only report on microbiological pathogens in the stool. Where provided, we will extract and analyse data from studies on the method of diarrhoea surveillance and reporting, severity of diarrhoea, hospital admission and measures taken by individuals in response to diarrhoea.
- Adverse events.
Search methods for identification of studies
We will attempt to identify all relevant studies regardless of language or publication status (published, unpublished, in press, ongoing).
We will search the following databases using the search terms detailed in Appendix 1: Cochrane Infectious Disease Group Specialized Register; Cochrane Central Register of Controlled Trials (CENTRAL), published in The Cochrane Library; MEDLINE; EMBASE; and LILACS. We will also search Chinese-language databases available under the Wan Fang portal using the search terms detailed in Appendix 1 or their Chinese-language equivalents. We will also search the metaRegister of Controlled Trials (mRCT) using 'diarrhea' and 'sanitation or latrine or toilet or privy or disposal' as search terms.
We will search the following conference proceedings of the following organizations for relevant abstracts: International Water Association; and Water, Engineering and Development Centre, Loughborough University, UK.
Organizations and pharmaceutical companies
We will contact researchers and organizations including Water, Sanitation and Health Programme of the World Health Organization; World Bank Water and Sanitation Program; UNICEF Water, Environment and Sanitation; Environmental Health Project; IRC International Water and Sanitation Centre; Foodborne and Diarrheal Diseases Branch, Division of Bacterial and Mycotics Diseases, Centers for Disease Control and Prevention (CDC); US Agency for International Development (USAID); and the UK Department for International Development (DFID) for unpublished and ongoing trials.
We will also check the reference lists of all studies identified by the above methods.
Data collection and analysis
Selection of studies
Thomas Clasen (TC) and Kristof Boeston (KB) will independently review the titles and abstracts resulting from the searches and select all studies that potentially fall within the inclusion criteria for the review. After obtaining full copies of all such studies, we will independently determine if the trial meets such inclusion criteria. Where we agree, we will either include or exclude the trial. Where we are unable to agree, we will consult Sandy Cairncross (SC) who will make the final decision. Any studies that TC or KB propose to include but which were ultimately determined by SC not to be included will be identified together with the reason for exclusion in the 'Characteristics of excluded studies'.
Data extraction and management
One author will use a pre-piloted form to extract and record the data described in Appendix 2, and attempt to contact authors to supply missing data. We will record morbidity based on the measure used in the trial, but where possible will recalculate morbidity based on the available data. One author will enter the extracted data into Review Manager 5.
Assessment of risk of bias in included studies
Two authors will independently assess the risk of bias (methodological quality) of each trial using generation of allocation sequence, allocation concealment, blinding, and loss to follow up.
We will classify generation of allocation sequence − the process used to generate the randomization list − as adequate if the method used is described and the resulting sequences are unpredictable (eg computer-generated random numbers, table or random numbers, coin toss, drawing lots); unclear if stated that the trial is randomized, but the method is not described; or inadequate if sequences could be related to outcomes (eg according to case record number, date of birth, alternation).
We will classify allocation concealment − the process used to prevent foreknowledge of group assignment − as adequate if the participants and the investigators enrolling participants cannot foresee assignment; unclear if method is not described; or inadequate if participants and investigators enrolling participant can foresee upcoming assignment.
We will classify blinding − whether the participant or outcome assessor is blind to the intervention group − as double blind if the trial uses a placebo or double dummy technique such that neither the participant or the assessor knows whether or not participant receives the intervention; single blind if the participant or the assessor knows whether or not participant receives the intervention; or open if both participant and assessor knows whether or not participant receives the intervention.
We will classify the inclusion of randomized participants in the analysis as adequate if more than 90%, unclear, or inadequate if less than 90%.
Also, we will assess quasi-randomized controlled trials using the following criteria:
- Comparability of characteristics between intervention and control groups with respect to relevant baseline characteristics such as water quality, diarrhoeal morbidity, age, socioeconomic status, access to water, hygiene practices, and sanitation facilities. We will classify this as adequate if no substantial differences are present; unclear if not reported or not known if substantial differences exist; or inadequate if one or more substantial difference exists.
- Data collection for intervention and control groups at the same time. We will classify this as adequate if data collected at similar points in time; unclear if not reported or not clear from trial; or inadequate if data not collected at similar points in time.
Where we disagree on trial methodological quality, we will consult Wolf-Peter Schmidt (W-PS) who will make the final decision. We will perform sensitivity analyses on the overall results and on the relevant subgroups in each category where there are sufficient trials.
Assessment of reporting biases
We will produce funnel plots to explore the existence of publication bias, heterogeneity of results, and differences in methodological quality.
We will compile and analyse data using Review Manager 5. Although trials of environmental interventions such as sanitation assess outcomes on an individual level, the unit of randomization is often not the individual but a household, group of households, neighbourhood, or village. Some trials correct for this design effect by adjusting for the intra-cluster variance.
With regard to dichotomous data from individually randomized trials (if any), we will extract the rate ratio, risk ratio, or prevalence ratio based on the raw numbers if available, or based on the ratios reported by the authors. We will calculate 95% confidence intervals (CI) for these outcomes if the raw numbers are available; otherwise we will rely on the 95% CI given by the trial authors. We will extract continuous data, summarized by the arithmetic mean or the geometric mean, with the 95% CI given by the trial authors and synthesized using mean differences.
With regard to cluster trials, we will calculate the rate ratio, risk ratio, or prevalence ratio and 95% CI if the cluster-level risk/rate/prevalence values or (in the case of matched pairs trials) the corresponding ratios are reported. We will calculate overall point estimates and 95% CI as the mean of the log cluster-level data. If cluster-level disease rates are not reported, we will rely on the point estimate and 95% CI given by the trial authors provided that clustering has been accounted for in the analysis. In trials meeting the inclusion criteria but failing to adjust for clustering (or to provide the data to allow adjustment), we will extract the unadjusted point estimates but reject the 95% CI.
We will analyse trials that randomize at a cluster level and do not statistically adjust for the smaller confidence intervals associated therewith separately from trials that randomize at the individual level or trials that do adjust for clustering.
We will report the measure of effect as reported by the authors of each trial, whether it be risk ratios, rate ratios, odds ratios, or longitudinal prevalence ratios. In this context, longitudinal prevalence is the number of days with diarrhoea divided by the number of days under observation (Morris 1996). In using these various measures of effect, we note the design effect in treating all such measures of effect as equivalent for common outcomes such as diarrhoea and the debate about methodologies for converting such measures of effect into a single measure (Zhang 1998; McNutt 2003). While it would be possible to calculate a single measure of effect for most trials based on the raw study data, we are electing not to do so for the following reasons. In addition to adjustment for clustering, studies of diarrhoeal disease also frequently adjust for other common covariates, including age and repeated episodes within the same participant. Because these adjustments are appropriate, a re-calculation of a measure of effect based on raw data would ignore these important adjustments. To avoid the homologous treatment of these different measures of effect, we will include the pooled measures of effect in the comparisons only across trials reporting the same measure of effect.
Subgroup analysis and investigation of heterogeneity
We will perform tests for heterogeneity by visually examining the forest plots and by using the chi-squared test for heterogeneity with a 10% level of statistical significance (Egger 2001) and the I
Where appropriate to pool data and heterogeneity is detected, we will use the random-effects model. Where appropriate, we will generate a pooled measure of effect using a meta-analysis for all pooled trials and for the subgroups.
The editorial base for the Cochrane Infectious Diseases Group is funded by the UK Department for International Development (DFID) for the benefit of developing countries.
Appendix 1. Search methods: detailed search strategies
Appendix 2. Data to be extracted from included studies
Protocol first published: Issue 2, 2008
Contributions of authors
Sandy Cairncross and Thomas Clasen conceived of the review. All of the authors assisted in the design and development of the protocol, including the literature review used in the 'Background' section. Thomas Clasen and Kristof Bostoen developed the search strategy. Wolf-Peter Schmidt and Sophie Boisson provided additional epidemiologic and statistical support. Isaac C-H Fung assisted in developing the search strategy for the Chinese-language databases. Marion Jenkins, Beth Scott, and Steven Sugden provided technical advice on sanitation interventions. All authors provided general advice for the review, commented on the protocol, and gave final approval of the version to be published.
Declarations of interest
Sources of support
- No sources of support supplied
- WaterAid, UK.
- UNICEF, USA.