• Open Access

Are they protected? Immunity to vaccine-preventable diseases in healthcare workers at an Australian hospital

Authors


  • The authors have stated they have no conflict of interest.

Abstract

Objective: Australian guidelines for healthcare worker (HCW) vaccination were updated in 2010, and pre-employment assessment of new employees has previously been identified as a priority. We determined the vaccination status of a cohort of existing HCWs at a tertiary hospital in Melbourne, Victoria.

Methods: Random sampling of HCWs employed prior to 2006 with unknown/incomplete immunisation status was conducted between April and August 2011. Immunity to vaccine-preventable diseases (VPDs) was determined serologically (hepatitis B, varicella, measles, mumps, rubella) and by questionnaire (diphtheria, tetanus and pertussis), with vaccination by a nurse immuniser.

Results: Overall, 95 HCWs were evaluated. Mean age and duration of employment were 47.2 and 12.6 years, respectively. Forty-seven staff (49%) required vaccination to comply with Australian immunisation guidelines: 18% were non-immune to hepatitis B, 2% to varicella, 8% to measles, 19% to mumps and 13% to rubella. HCWs without serological hepatitis B immunity were all staff with clinical roles. Total costs were $7,527.34 (mean $222.79/HCW).

Conclusions: Immunity to VPDs among existing HCWs was inadequate. About half assessed HCWs were non-immune to at least one VPD, and non-immunity to hepatitis B was high. A comprehensive assessment strategy for existing employees is required to enhance vaccination coverage and compliance with national guidelines.

Implications: Adequately resourced ‘look-back’ immunisation assessment programs are required to reduce the risks of VPDs among existing staff and patients. Review of current approaches and national consensus regarding the need for mandatory strategies would assist this process.

Infection prevention strategies for healthcare workers (HCWs), including immunisation programs, are essential in healthcare facilities, given the potential risk of acquisition and transmission of vaccine-preventable diseases (VPDs) in clinical settings.1 In Australia, National Health and Medical Research Council (NHMRC) recommendations stipulate that prior to employment, all HCWs should be assessed and tested for a range of VPDs including hepatitis B, varicella, measles, mumps and rubella.2 Hospital outbreaks of VPDs3,4 underscore the importance of providing a comprehensive vaccination program, and vaccination of HCWs reduces absenteeism.5

Despite recommendations, Australian and international studies have reported suboptimal vaccination coverage for VPDs in HCWs.6–8 A cross-sectional survey at a Victorian hospital in 2002 found only 18% of HCWs to be fully vaccinated.9 Screening and vaccination of healthcare workers for VPDs is varied in Australia. Review of public and private hospitals in New South Wales (NSW) in 2003 found 50% of facilities reported pre-employment screening was performed for nursing staff, with even less (20%) for physicians. Routine assessment of measles and varicella immunity was performed at only one-third of centres.10 Subsequently, the NSW Health Policy Directive was released in 2011, mandating HCW assessment, screening and vaccination for newly recruited staff.11

Consistent with the Victorian Immunisation Strategy 2009–12,12 a mandatory pre-employment assessment and vaccination program was introduced for all new employees at the Peter MacCallum Cancer Centre in 2006. Prior to this time, assessment and vaccination was not mandated and compliance was not monitored. The objective of this study was to determine the vaccination status of a cohort of HCWs employed at this centre prior to the introduction of a mandatory policy. We also sought to determine the costs associated with assessment and vaccination of existing HCWs. We proposed that this cohort may be representative of HCWs at other centres, where screening and vaccination are not routinely performed.

Methods

Healthcare workers were considered eligible for participation in the study if they were employed at the Peter MacCallum Cancer Centre prior to 2006 and if immunisation status was unknown or incomplete. To ensure representation by high and medium risk areas within the study centre, payroll listings of staff employed in haematology, surgical oncology, pathology and outpatient units were obtained. Eligible staff were randomly selected and invited to participate via email correspondence. Telephone and further email contact was attempted up to five times, after which time HCWs were categorised as ‘contact unsuccessful’.

HCWs were requested to complete a questionnaire capturing demographic data (age, date of birth and employment category) and previous vaccination history, and to provide any available vaccination documentation. Initial assessment and pre-test counselling was conducted by an accredited nurse immuniser. Serological testing was performed by an external pathology service for hepatitis B surface antibodies (HepBsAb) and varicella, measles, mumps and rubella-specific IgG antibodies. Serology was performed where there was no previous documentation or if history of disease or previous vaccination was uncertain. Non-immune HCWs were offered vaccination, in accordance with guidelines in the Australian Immunisation Handbook.13

A HepBsAb titre <10 mIU/mL was considered indicative of non-immunity to hepatitis B. If hepatitis B vaccination was required, post-vaccination serology was performed. If post-vaccination HepBsAb titre was <10 mIU/mL, hepatitis B surface antigen and core antibody were evaluated. National immunisation guidelines14 were followed for vaccination assessment of pertussis (dTpa booster if >10 years since previous vaccination). Diphtheria and tetanus vaccination status were opportunistically evaluated (dTpa booster if age >50 years and no booster for tetanus in previous 10 years).

Initial assessment of eligible HCWs was performed between April and August 2011. Results were reviewed by a study nurse and infectious diseases physician. A project co-ordinator (0.4 Equivalent Full Time) was responsible for scheduling assessment and follow-up appointments. All serological and vaccination results were stored in a confidential database accessible to the study nurse and co-ordinator.

Stata 9.015 was used for data analysis. Proportional outcomes were calculated according to HCW category, NHMRC healthcare worker category (A or B), age and gender. NHMRC category A is defined as HCWs with direct contact with blood or body substances, and category B is defined as HCWs who have indirect contact with blood or body substances, but may be exposed to infection by respiratory transmission.2 Mean cost per HCW (AUD$) was estimated based on expenditure for serological testing, vaccines administered and nurse immuniser, physician and administrative wages. The estimated costs did not account for material costs such as database development and purchase of a vaccination fridge.

Ethics approval was obtained from the Peter MacCallum Cancer Centre human research ethics committee. Participation was voluntary and completion of the staff questionnaire signified implied consent for participation in the study.

Results

At the time of the study, 945 of 2,567 staff were employed prior to 2006. Of these, 169 were invited to participate, and none of these had complete vaccination records. Ninety-five of the invited staff responded and were assessed (response rate 56%). Participating HCWs were classified according to occupation: nursing staff (n = 44, 44%), medical staff (n = 15, 16%), allied health staff (n = 18, 19%), laboratory staff (n = 6, 6%) and administrative staff (n = 12, 13%). According to NHMRC risk categories, 85 (89%) and 10 (11%) were represented by categories A and B, respectively. Ages ranged between 26 and 67 years (mean ± standard deviation, 47.2 ± 11.4 years); 73 were female and 22 were male. Characteristics of participant HCWs are summarised in Table 1. About one-third (31%) of tested HCWs were born prior to 1966. The average duration of employment was 12.6 years (standard deviation 7.6 years).

Table 1. Characteristics of participating health care workers.
 Nursing (N=44)
 n (%)
Medical (N=15)
 n (%)
Allied Health (N=18)
 n (%)
Laboratory (N=6)
 n (%)
Admin/Clerical (N=12)
 n (%)
Total (N=95)
 n (%)
Age category (y)      
 20–295 (11)1 (17)1 (8)7 (7)
 30–3913 (30)3 (20)5 (28)1 (17)2 (17)24 (25)
 40–4912 (28)7 (47)2 (11)1 (17)2 (17)24 (25)
 50–598 (18)3 (20)8 (44)2 (33)5 (42)26 (27)
 ≥606 (14)2 (13)3 (17)1 (17)2 (17)14 (15)
Gender      
 Female40 (91)4 (27)14 (78)4 (67)11 (92)73 (77)
 Male4 (9)11 (73)4 (22)2 (33)1 (8)22 (23)
Mean (SD) duration of employment (y)11.6 (7.0)10.1 (4.6)16.2 (10.3)14.5 (8.6)13.3 (6.3)12.6 (7.6)

Eighty-five HCWs were tested for hepatitis B surface antibodies and 15 (18%, 95%CI 9.9–29.1%) were non-immune (Table 2). The majority of these were nursing, allied health and medical staff (33%, 33% and 20%, respectively). Eleven were administered a hepatitis B vaccination course and, of these, eight were immune following vaccination. Five were lost to follow up or did not complete a full hepatitis B vaccination course and two remained non-immune following vaccination (serological non-responders).

Table 2. Serological status of participating health care workers according to NHMRC employment category.
 Category Aa (N=85)
 n (%)
Category Bb (N=10)
 n (%)
Total (N=95)
 n (%)
  1. a. Category A defined as health care workers with direct contact with blood or body substances.

  2. b. Category B defined as health care workers who have indirect contact with blood or body substances, but may be exposed to infection by respiratory transmission.

Blood borne virus
  Hepatitis B surface antibodies (not detected)

 15 (18)

 –

 15 (18)
Other infections
  Varicella zoster virus IgG (not detected)
  Measles virus IgG (not detected)
  Mumps virus IgG (not detected)
  Rubella virus IgG (not detected)

 2 (2)
 7 (8)
 15 (18)
 13 (13)


 1 (10)
 4 (40)
 2 (20)

2 (2)
 8 (8)
 19 (20)
 13 (14)

All HCWs were tested for immunity to varicella, measles, mumps, and rubella (Table 2). Two percent were non-immune to varicella, 8% to measles, 20% to mumps and 14% to rubella. Of those who were not immune to mumps, nursing staff comprised 32%, allied health, medical and administrative staff 21% respectively, and laboratory staff (5%). Nursing staff made up the vast majority of HCWs who were not immune to rubella (46%). Twenty-four (25%) participants reported no or uncertain vaccination status for diphtheria, tetanus or pertussis.

Of all participating HCWs, 47 (49%) required one or more vaccinations and 15 (16%) required two or more vaccinations to comply with Australian immunisation guidelines.

An estimated mean cost per participating HCW, inclusive of serological testing, vaccines, medical review and nurse immuniser EFT, was $222.79. These costs are summarised in Table 3. Overall costs, excluding administrative resources, were estimated to be $7,527.34.

Table 3. Itemised costs for program implementation (AUD$).
ItemUnit cost ($)NOverall cost ($)
  1. a. Engerix-B (contains 20 μg recombinant hepatitis B surface antigen protein).

  2. b. Varilrix (contains not less than 103.3 plaque-forming units of attenuated varicella-zoster virus).

  3. c. Priorix (contains not less than 103.0 CCUID50 of the Schwarz measles, not less than 103.7 CCUID50 of the RIT 4385 mumps and not less than 103.0 CCUID50 Wistar RA 27/3 rubella virus strains).

  4. d. Boostrix (contains ≥2 IU diphtheria toxoid, ≥20 IU tetanus toxoid, 8 μg PT, 8 μg FHA and 2.5 μg PRN).

Hepatitis B serology13.40851,139.00
Measles, mumps, rubella serology33.25953,158.75
Varicella serology15.75951,496.25
Hepatitis B vaccinea14.8033488.40
Varicella vaccineb46.894187.56
Measles, mumps, rubella vaccinec21.7821457.38
Diphtheria, tetanus, pertussis vaccined25.0024600.00
Study nurse, coordinator, physician wages13,638.00

Discussion

This study of a cohort of existing Australian HCWs identified that almost half the surveyed staff were not immune to at least one VPD, with high proportions of staff susceptible to mumps (20%), hepatitis B (18%) and rubella (14%). About two-thirds of participants consisted of nursing and medical staff. Estimates of cost appear marginal compared to the costs of containing and managing hospital outbreaks of VPDs,16–18 and these estimates may allow future planning of an expanded program for remaining HCWs at our centre.

Non-immunity to hepatitis B among surveyed HCWs who have direct contact with blood or bodily substances was high, with close to one-fifth being non-immune. This is similar to previous European experience7 but lower than reports by other Australian healthcare facilities.9,10,19 An evaluation of two healthcare facilities following the implementation of a policy directive in NSW found that about one-third of staff had no immunity to hepatitis B.19 Further education regarding hepatitis B vaccination and more stringent policy is required to improve uptake of hepatitis B vaccination in Victorian HCW.

Serologically confirmed non-immunity to mumps (20%) and rubella (14%) was high, compared with measles (8%). This is in contrast to lower proportions of HCWs who were non-immune to measles, mumps and rubella (3.5%, 7.4% and 6.6% respectively) reported by Vagholkar et al.19 About 63% and 92% of HCWs in our study who were not immune to mumps and rubella were born before 1966, and were therefore not targeted as part of the standard measles, mumps and rubella immunisation schedule in Australia.20 The higher median age of participants in the current study may explain the observed high proportion of non-immunity to mumps and rubella.

Guidelines for HCW vaccination and screening vary widely across jurisdictions in Australia, sometimes with different strategies employed for existing and new employees. Only the states of NSW and Queensland have enforced mandatory HCW assessment and vaccination policies. In Queensland, it is a condition of employment that workers with direct patient contact or exposure to blood and body fluids are assessed for immunity and vaccinated against Hepatitis B,21 while in NSW, the policy directive implemented in 2002 requires new employees to provide evidence of immunity against specified VPDs.22 However, vaccination uptake has remained suboptimal following the introduction of the policy,23 likely due to the fact that individual healthcare facilities have been responsible for implementation.

In Victoria, mandatory screening is not enforced and practices are therefore varied across health services. The scope of HCW immunisation screening is largely unknown, formal monitoring of compliance is not performed, and unprotected clinical staff may inadvertently perform high risk activities. A strategy comparable to that employed in NSW is required to ensure appropriate screening and vaccination of HCWs. However, adequate resourcing, leadership and communication must be available to avoid the pitfalls experienced by some healthcare facilities in that jurisdiction.

Reasons for not undertaking vaccination were not examined in this study. Previous studies have found that HCWs fail to be vaccinated for many reasons – concern for vaccine safety and side effects, perceived vaccine inefficacy, cost, difficulty in accessing vaccination service and inadequate education of staff regarding policy.9,24,25 These must be identified prior to implementation of strategies for risk reduction in Victorian healthcare facilities. Furthermore, many vaccination programs target new employees, neglecting a group of possible at-risk existing employees. At our centre, the program for assessment of new employees is rigorous, achieving 81% and 84% compliance with policy for staff classified as NHMRC categories A and B, respectively (2011).

Our findings may not be applicable to all Victorian HCWs as the sample was from a single centre, and liable to selection bias. Given the small sample size, it is possible that at-risk HCWs were under-represented, as some existing workers may have undergone previous assessment either voluntarily or as follow up due to contact tracing activities. Recruitment of participants resulted in over-representation of nursing staff and under-representation of allied health and laboratory staff in our study when compared to the proportion employed overall. Country of birth was not included in the questionnaire, which may have implications on generalisability of results if HCWs originated from an endemic country. While we assessed immunity to hepatitis B, measles, mumps, rubella and varicella, influenza vaccination status was not assessed. Similar to the policy directive in NSW, annual influenza vaccination is a requirement at our centre, but has not yet been made a mandatory condition of employment.26

Common to all serostudies, measurable antibody titres may not equate to clinical immunity. Similarly, lack of detectable antibody post vaccination may not equate to disease susceptibility. However, immunity in our study was measured and defined in accordance with NHMRC guidelines. Clinical endpoints and memory T cell function were not reviewed in the current study.

In summary, this study identified that almost half the HCWs assessed at a Victorian healthcare facility were non-immune to one or more VPD, representing a pool of staff that may be significantly affected in the event of an outbreak or occupational exposure. A more robust ‘look-back’ strategy is required within our centre to target HCWs employed prior to the introduction of a vaccination policy, and uniform strategies must be developed within the state of Victoria to mitigate occupational risks. While successful promotion of immunisation has occurred in Australia over the past 3 decades, these efforts have largely concentrated on implementation of immunisation programs in paediatric and indigenous populations and patients with chronic medical conditions. The occupational safety of HCWs must also be prioritised. National consensus regarding adherence to guidelines and appropriate priorities and targets for HCW immunisation programs would assist jurisdictions to work towards mandated approaches.

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