Prevalence of hepatitis A virus infection among sewage workers in Singapore

Evaluation of Seasonal Variation on the Health Risks Using the Quantitative Microbial Risk Assessment Approach in a Wastewater Treatment Plant in Hamadan, Iran

BACKGROUND

Wastewater treatment plants (WWTPs) are a source of airborne bacterial contamination that can pose health risks to staff. The aim of this study was to evaluate seasonal variations in the health risks of exposure to Staphylococcus aureus bioaerosols using the quantitative microbial risk assessment (QMRA) approach in a WWTP in Hamadan, Iran.

STUDY DESIGN

This was a descriptive cross-sectional study.

METHODS

This study determined the emission concentrations of S. aureus bioaerosols in summer and winter. Then, the health risks of three exposure scenarios (the worker, field engineer, and laboratory technician) were evaluated using the QMRA approach. The bioaerosol samples were collected every 12 days in both summer and winter of 2021 with a nutrient agar using a single-stage cascade impactor (Quick Take 30, SKC Inc.) in both outdoor and indoor environments.

RESULTS

The results demonstrated that in both seasons, S. aureus bioaerosol concentrations in outdoor and indoor environments were below the standard established by the American Conference of Governmental Industrial Hygienists (500 CFU/m3 ). While in summer, the annual infection risks and the disease burden for the three exposure scenarios in both outdoor and indoor environments were higher than the United States Environmental Protection Agency (≤10-4 pppy) and the World Health Organization (WHO) (≤10-6 DALYs pppy-1) benchmarks, respectively.

CONCLUSION

The findings provided high health risks for staff in the three exposure scenarios of an indoor environment, which should not be ignored, as well as emphasizing the use of the QMRA approach to estimate health risks caused by occupational exposure to bioaerosols and taking executive measures to protect staff working in the WWTPs.

Occupational health outcomes among sanitation workers: A systematic review and meta-analysis

Background

Sanitation workers are essential to global public health and societal wellbeing. However, the health risks and outcomes associated with exposure to occupational risk factors among sanitation workers are neither well understood nor well quantified. We undertook a systematic review to (1) identify occupational risk factors among sanitation workers and (2) assess the effect of occupational exposure to human fecal sludge and wastewater on selected health outcomes among these workers.

Methods

We searched four databases (i.e., PubMED, MEDLINE, EMBASE, and LILACS) for eligible studies from inception through to January 01, 2020. The included population was workers ≥15 years engaged, formally or informally, in installing, operating, servicing, cleaning or emptying a sanitation technology at any step of the sanitation chain. The included comparator was workers in other occupations or the general population. Eligible outcomes were: mortality (any or all causes), gastroenteritis, occupational injuries, respiratory diseases, musculoskeletal disorders, and mental and social health conditions. Risk of bias was assessed separately on exposure assessment and health outcome using a modified Liverpool Quality Assessment Tool (LQAT). We pooled sufficiently homogenous studies using inverse variance meta-analysis with random effects.

Results

A total of 65 studies (9 cohort studies, 56 cross-sectional studies) met the inclusion criteria. One quarter of studies (n = 15) were from middle-income countries. Few studies assessed occupational risk factor exposures directly; most assigned exposure via proxy of occupation of sanitation worker. We judged nearly all studies to have “high risk of bias” in exposure and outcome assessment. Despite these limitations, the consistency of the overall evidence suggests that sanitation workers are at increased risk of gastroenteritis and respiratory conditions, and may be at increased risk of musculoskeletal disorders and mental/social health conditions. The pooled odds ratio for hepatitis A--the only outcome deemed suitable for meta-analysis--was 2.09 (95% Predicted Interval: 1.39–3.00, 12 studies). There was conflicting evidence from studies of increased risk of mortality; only one study reported on injuries.

Conclusion

Despite a large number of studies, there is limited evidence to date of the health risks faced by sanitation workers, particularly among groups that may be at particular risk-- women, informal workers and those living in low-income countries. Nevertheless, the research to date provides suggestive evidence of elevated occupational risk among sanitation workers across a range of health condition. More research is needed to improve the current bodies of evidence for all included health outcomes to be able to quantify disease burden among this occupational group.

Quantitative microbial risk assessment for occupational health of temporary entrants and staffs equipped with various grade PPE and exposed to microbial bioaerosols in two WWTPs

Purpose

This study was to evaluate the occupational health risks of infection from Gram-negative bacteria and Staphylococcus aureus bioaerosols to temporary entrants and staffs equipped with various grade personal protection equipment (PPE) related to wastewater treatment plants (WWTPs).

Methods

This study determined the emission concentrations of Gram-negative bacteria and Staphylococcus aureus bioaerosols from two WWTPs under various aeration modes. Then, a strict quantitative microbial risk assessment (QMRA) was performed on several exposure scenarios associated with occupational health risks of temporary entrants (researchers, visitors, and inspectors) and staffs (field engineer and laboratory technician).

Results

Although the bioaerosol concentrations were generally regarded as safe according to existing standards, these bioaerosols’ health risks were still unacceptable. The microbial bioaerosols posed considerable infection health risks in WWTPs. These risks were generally above the WHO and US EPA benchmarks. The health risks of females were always smaller than those of male of grown-up age group. Staffs that had been exposed to bioaerosols for a long time were found to have higher health risks compared with temporary entrants. In addition, field engineers equipped with PPE rendered low health risks, thus revealing that wearing PPE could effectively reduce the occupational health risks.

Conclusion

This study provided novel data and enriched the knowledge of microbial bioaerosol emission’s health risks from various aeration modes in WWTPs. Management decisions could be executed by authorities on the basis of the results of QMRA for field engineers equipped with PPE to reduce the related occupational health risks.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00420-021-01663-5.

Infectious diseases and migrant worker health in Singapore: a receiving country's perspective

BACKGROUND

Approximately 1.4 million migrant workers reside in Singapore, presenting unique infectious disease challenges to both migrants and Singapore.

METHODS

A Pubmed, MEDLINE (Ovid), EBSCO Host (Global Health) and Google Scholar search was performed for both peer, non-peer reviewed articles and reports relevant to migrant health in Singapore, published between 1 January 1989 and 1 September 2016. Additional studies were identified from citations within searched articles. We also reviewed published data and policy documents from the Ministries of Health and Manpower, Singapore.

RESULTS

A significant proportion of malaria, enteric fevers, hepatitis A and E and tuberculosis diagnosed in Singapore involve migrant workers. From the 1990-2000 through 2009-11, while malaria and hepatitis A cases have decreased and remain sporadic, enteric fevers and tuberculosis cases have increased, possibly due to greater influx of migrant workers. Hepatitis E numbers remain low but migrant workers account for half of diagnosed cases. In an interplay of immune naivete, work and living conditions, migrants in the construction industry are at higher risk of arboviral infections such as dengue, Zika and chikungunya. Infections such as chikungunya were likely introduced into Singapore by travellers including migrant workers from the Indian subcontinent but autochthonous transmission continued due to the presence of competent mosquito vectors. There is less data regarding sexual health, networks and infections amongst migrant workers, an area which merits further attention.

CONCLUSIONS

Migrant workers appear to be at higher risk than Singaporeans for specific infectious diseases, probably due to a complex interplay of several factors, including higher disease prevalence in their countries of origin, socio-economic factors, their living conditions in Singapore and financial, language and cultural barriers to healthcare access. Receiving countries need improved surveillance, expansion of preventive measures and decreased barriers to healthcare access for migrant workers.

Characterization of aerosol emissions from wastewater aeration basins

The emission of particulate matter (PM10 and PM2.5) and ammonia (NH3) by aeration processes at wastewater treatment plants (WWTPs) with and without odor control units was examined. Local concentrations of PM2.5, PM10, and NH3 at the aeration basins were within urban ranges. Emission fluxes of NH3 and PM2.5 for a medium-sized WWTP were determined to be 136 g day(-1) and 43 g day(-1), respectively, which are not substantial emission fluxes for urban environments. Odor control treatment using a granulated activated carbon bed reduced aerosol and NH3 emissions substantially. Detection of sterols, in particular the fecal sterol campesterol, in the PM clearly demonstrates aerosolization of wastewater components in the aeration process. The presence of campesterol in PM2.5 at a remote fenceline location in a WWTP facility illustrates that wastewater components are aerosolized in the fine PM fraction and transported beyond the facilities.

IMPLICATIONS

Wastewater treatment plants are potential emission sources of particulate matter and gases. This study characterized particulate matter emissions from aeration basins and quantified emissions fluxes of particulate matter and NH3. While fine and coarse particles as well as NH3 are being emitted, the overall emissions are small compared to other urban sources. However, fecal steroid presence in particles at the fence of a treatment plant demonstrates that wastewater material is getting aerosolized and transported beyond the facilities.

Virus hazards from food, water and other contaminated environments

Numerous viruses of human or animal origin can spread in the environment and infect people via water and food, mostly through ingestion and occasionally through skin contact. These viruses are released into the environment by various routes including water run-offs and aerosols. Furthermore, zoonotic viruses may infect humans exposed to contaminated surface waters. Foodstuffs of animal origin can be contaminated, and their consumption may cause human infection if the viruses are not inactivated during food processing. Molecular epidemiology and surveillance of environmental samples are necessary to elucidate the public health hazards associated with exposure to environmental viruses. Whereas monitoring of viral nucleic acids by PCR methods is relatively straightforward and well documented, detection of infectious virus particles is technically more demanding and not always possible (e.g. human norovirus or hepatitis E virus). The human pathogenic viruses that are most relevant in this context are nonenveloped and belong to the families of the Caliciviridae, Adenoviridae, Hepeviridae, Picornaviridae and Reoviridae. Sampling methods and strategies, first-choice detection methods and evaluation criteria are reviewed.

Virus hazards from food, water and other contaminated environments

Numerous viruses of human or animal origin can spread in the environment and infect people via water and food, mostly through ingestion and occasionally through skin contact. These viruses are released into the environment by various routes including water run‐offs and aerosols. Furthermore, zoonotic viruses may infect humans exposed to contaminated surface waters. Foodstuffs of animal origin can be contaminated, and their consumption may cause human infection if the viruses are not inactivated during food processing. Molecular epidemiology and surveillance of environmental samples are necessary to elucidate the public health hazards associated with exposure to environmental viruses. Whereas monitoring of viral nucleic acids by PCR methods is relatively straightforward and well documented, detection of infectious virus particles is technically more demanding and not always possible (e.g. human norovirus or hepatitis E virus). The human pathogenic viruses that are most relevant in this context are nonenveloped and belong to the families of the Caliciviridae, Adenoviridae, Hepeviridae, Picornaviridae and Reoviridae. Sampling methods and strategies, first‐choice detection methods and evaluation criteria are reviewed.

Virus hazards from food, water and the environment, their reservoirs and routes of transmission; Sampling methods and sampling strategies thereof, including the first choice test methods, and criteria for data evaluation are described.

Changing Epidemiological Patterns of Hepatitis A Infection in Singapore

Introduction: Singapore has experienced remarkable socioeconomic progress over the last few decades, with a corresponding rise in standards of sanitation and living conditions. We undertook a study to describe its epidemiological trends of hepatitis A over the last 2 decades. Materials and Methods: We analysed the epidemiological data on all laboratory-confirmed cases of hepatitis A from 1990 to 2009. We also described 3 outbreaks which occurred in 1991, 1992 and 2002. To determine the changing prevalence of hepatitis A virus (HAV) infection, we compared the findings from a seroepidemiological study conducted in 1993 with earlier surveys in 1975 and 1984/1985. Results: The incidence of indigenous hepatitis A cases per 100,000 population declined significantly from 1.8 in 1989 to 0.7 in 2009, and more than half were imported. While majority of the imported cases were Singapore residents, the proportion of imported cases among Singapore residents had decreased significantly. Most of the Singapore residents contracted the disease from Southeast Asia and the Indian subcontinent. The overall prevalence of HAV infection in the population declined from 31.8% in 1984/85 to 25.9% in 1993. Conclusion: The incidence and seroprevalence of hepatitis A in Singapore are comparable to other developed countries. As Singapore is situated in a region highly endemic for HAV, it is very vulnerable to the introduction of the disease because of the high volume of regional travel and import of food, especially shellfish. While we note that there have been no further shellfish-associated outbreaks since 2002, sustained vigilance, strict control of food import by the authorities and public health education on the risk of consuming shellfish, especially cockles, raw and half-cooked, should be maintained. Key words: Cockles, Imported cases, Outbreaks, Oysters, Shellfish, Seroprevalence

Vaccinations for waste-handling workers. A review of the literature

A review of the literature relating to the need for vaccination against infectious disease in the solid waste industry was conducted, focusing on hepatitis A, hepatitis B and tetanus. Databases (Medline, PreMedline, EMBASE, CINAHL, Current Contents, Cochrane Database, HTA Database, DARE, OSHROM) were searched up to and including August 2003. Articles were included in the review if they reported the prevalence of immunity to hepatitis A, hepatitis B or tetanus in solid waste workers or the incidence of clinical infection with any of these diseases. Papers about hazardous or medical waste, incineration or other infectious diseases were excluded. Forty-four papers constituted the evidence database. Only one paper studied the prevalence of antibodies to hepatitis A and hepatitis B in solid waste workers compared with sewage plant workers and office workers, and no difference was found between these groups of workers. There was some evidence to support a theoretical risk of infection with hepatitis A, B and tetanus; however, no studies could be found of the risk of these diseases in solid waste workers. No single cases of these diseases being acquired occupationally in solid waste management were identified in the literature. Workers in the solid waste industry may theoretically be at increased risk of acquiring infectious diseases occupationally. However, at present no studies could be found which have documented this risk.

Work-related symptoms and inflammation among sewage plant operatives

Sewage operatives at five sewage treatment plants (n = 59) and controls not exposed to sewage (n = 55) were examined to determine work-related symptoms and inflammatory responses. Symptoms were elicited using a questionnaire, and spirometry was performed. Inflammatory markers were determined in blood and nasal lavage. Workplace endotoxin and hydrogen sulfide were measured and adeno- and enterovirus antibodies were evaluated in blood. Gastrointestinal and airway symptoms, joint pains, unusual tiredness, and toxic pneumonitis were more common among operatives, and the proportion of blood neutrophils was higher among operatives as compared with controls. A relationship was found between several reported symptoms and the inflammatory markers. Hydrogen sulfide levels were very low. Endotoxin levels were generally low, but high at some work sites.

Travel health knowledge, attitudes and practices among Australasian travelers

BACKGROUND

Although the Asia Pacific region is the focus of the fastest-growing tourist and travel industry, few data are available on the knowledge, attitudes and practices (KAP) of travelers from this region with regard to travel-related infectious diseases.

METHODS

We conducted a cross-sectional survey among travelers at the departure lounges of five airports in Australasia (Singapore, Kuala Lumpur, Taipeh, Melbourne, Seoul) whose travel destinations were Asia, Africa or South America. Two standardized questionnaires directed towards KAP in travel health, travel immunizations and malaria were administered.

RESULTS

Of 2,101 respondents (82% Asian, 17% Western), 31% had sought pretravel health advice and only 4% sought travel health advice from the travel medicine specialist. The risk of vaccine-preventable infectious diseases and malaria at the destination country was perceived to be low. Overall, fewer than 5% of travelers had been vaccinated in preparation for their trip. The most frequent travel vaccinations were for hepatitis A and B. Only 40% of travelers to malaria-endemic areas carried malaria prophylaxis. Compared to Western travelers, those of Asian nationality were significantly less likely to obtain pretravel advice and malaria prophylaxis and to receive travel vaccinations.

CONCLUSION

There is an urgent need for increased awareness about travel-related infectious diseases among Asian travelers, and greater uptake of pretravel health advice, vaccinations and malaria prophylactic measures.

Increased Risk of Hepatitis E in Sewage Workers from India

Considering feco-oral transmission of hepatitis E virus (HEV), the risk of the infection was assessed among sewage workers. On the basis of the close contact with sewage, the participants (n = 147) were divided into sewage workers (n = 92) and others (n = 55); none used personal protective equipment (eg, coveralls, boots, gloves) Age-matched individuals from lower socioeconomic status and without any exposure to sewage were used as controls. IgG-anti-HEV positivity in enzyme-linked immunosorbent assay was significantly higher (P < 0.01) among staff members (83/147, 56.5%) than the controls (19%). A significant rise in anti-HEV positivity (P < 0.05) was recorded in sewage workers working for >5 years. Multivariate regression analysis identified contact with sewage as the independent variable associated with anti-HEV positivity. Strict adherence to good working practices must take top priority for protection of these workers from sewage pathogens.

Wastewater exposure and health--a comparative study of two occupational groups

AIMS

To investigate whether wastewater workers are at increased risk of developing cancer.

METHODS

Two cohorts of workers employed by the City of Copenhagen, 591 wastewater workers and 1545 water supply workers (controls), were followed from 1965 until 1998. These two cohorts were compared in terms of cause specific mortality and cancer incidence.

RESULTS

The wastewater workers' mortality exceeded that of the controls (relative risk (RR) = 1.25, 95% CI: 1.03 to 1.51). A similar small excess was seen for cancer incidence (RR = 1.27, 95% CI: 0.97 to 1.67). Though rare, there was a strongly increased incidence of primary liver cancer among the wastewater workers (RR = 8.9, 95% CI: 1.5 to 51.5).

CONCLUSION

The excess mortality seen among the wastewater workers was smaller than originally feared. It may partly have been due to their occupational exposure, and for preventive purposes, exposure to wastewater and sludge should be minimised. The possibility that sewage exposure confers an increased risk of primary liver cancer deserves further investigation.

Risk groups for hepatitis A virus infection

We report the conduct and results of a systematic search for evidence of risk of infection with hepatitis A virus (HAV) among blood transfusion recipients, travellers, the military, healthcare workers, sewage workers, foodhandlers, day care assistants, institutionalised subjects, blood transfusion recipients, drug addicts, homosexuals, prisoners and other risk groups such a liver transplantees. We report our recommendations for the use of the HAV vaccine in these groups.

Prevalence of hepatitis A virus infection among sewage workers in Georgia

BACKGROUND

Wastewater (WW) workers could have opportunity for direct contact with raw sewage, which might contain hepatitis A virus (HAV).

METHODS

A serologic survey of WW workers and a comparison population of roads and drainage workers (RD). Factors potentially associated with anti-HAV positivity were evaluated in univariate and multivariate analyses.

RESULTS

Among the 365 WW workers, overall anti-HAV prevalence was 38%, similar to that (35%) of the 166 RD workers (P = 0.5). Prevalence varied by wastewater job type from 45% among the 164 field crew workers to 32% among the 201 treatment plant workers. In multivariate modeling, factors associated with anti-HAV positivity included age > or = 40 years (odds ratio [OR] = 2.4; 95% CI = 1.6-3.7), black compared to other races (OR = 2.4; 95% CI = 1.5-3.8), birth outside the United States (OR = 7.5; 95% CI = 3.0-18.6), a high school education or less (OR 2.1; 95% CI = 1.4-3.2) and work on the field crew compared to RD work (OR 1.6; 95% CI = 1.1-2.4).

CONCLUSIONS

These results are consistent with no or a small increased risk of hepatitis A among WW workers, and do not provide a clear mandate for hepatitis A vaccination of these workers. Am. J. Ind. Med. 43: 172-178, 2003.

Work related symptoms among sewage workers: a nationwide survey in Sweden

AIMS

To assess the risk for work related symptoms among sewage workers in Sweden using a postal questionnaire.

METHODS

All municipalities in Sweden were contacted and asked to provide addresses of sewage workers and controls. Controls were recruited among other municipal workers not exposed to sewage, such as workers in drinking water plants and gardeners. A questionnaire was sent to the subjects and after two reminders, the response rate was 74% among sewage workers and 59% among controls.

RESULTS

Significantly increased risks for airway symptoms, chronic bronchitis, and toxic pneumonitis, as well as central nervous system symptoms such as headache, unusual tiredness, and concentration difficulties were found among the sewage workers compared with controls. Furthermore, an increased risk for non-specific work related gastrointestinal symptoms was found among the sewage workers; an increased risk for joint pains, related to pains in more than four joints but not with loading, was also found.

CONCLUSIONS

The results of this questionnaire survey show an increased risk for airway, gastrointestinal, and general symptoms such as joint pains and central nervous system symptoms among sewage workers. Clinical investigations are needed to determine the cause of the reported symptoms among sewage workers, and further field studies are required to assess the causal agents.

Hepatitis A in workers exposed to sewage: a systematic review

OBJECTIVES

To assess whether the scientific literature supports the hypothesis that workers exposed to sewage are at higher risk of hepatitis A (HA).

METHODS

All original papers reporting epidemiological studies published in English, French, or German which reported on the risk of HA infection in workers exposed to sewage were eligible. They were identified by several methods and each original paper was assessed independently with a checklist by two people. Studies were classified according to the strength of their design. Non-eligible studies were also examined to assess the impact of publication bias. If the risk estimates diverged widely, causes for heterogeneity were assessed. A distinction was made between seroprevalence studies based on subclinical HA (defined only by the presence of anti-HA antibodies) and clinical HA.

RESULTS

17 eligible studies were identified. No indication of an increased risk of clinical HA could be found. For seroprevalence the studies with the strongest design suggested a slightly increased risk of subclinical HA with an odds ratio (OR) <2.5. Heterogeneity was considerable and precluded a meta-analysis. Considering non-eligible studies would still decrease the OR.

CONCLUSIONS

The systematic review does not confirm an increased risk of clinical HA in workers exposed to sewage. An increased risk of subclinical HA cannot be excluded but the association between seropositivity and exposure to sewage was not strong and became still weaker if publication bias was taken into account.

Health effects among employees in sewage treatment plants: A literature survey

BACKGROUND

Over the years, there have been regular reports in the media of work-related symptoms among employees at sewage treatment plants. Concern has spread among employees over the lack of knowledge of risk agents' symptoms, and diseases in that environment. This paper reviews the investigations of health risks in employees working in the sewage treatment plants.

METHODS

A literature search was performed with the search terms; sewage, waste water, health effects, infection, and health hazards. Articles on health effects in relation to sewage were selected.

RESULTS

Work in sewage water plants can involve exposure to different types of microorganisms and chemicals. The bacterial exposure is dominated by bacteria that naturally occur in nature. However, different bacteria and viruses that give rise to infections can be present in this environment and thus there exists a risk of infection, especially of hepatitis A. Investigations suggest that gastrointestinal tract symptoms are more common among employees at sewage treatment plants than among controls. Respiratory symptoms, fatigue, and headache have also been reported in several investigations. The cause of the symptoms is unknown, although certain data suggest that they are caused by inflammation. The results suggest that endotoxin in Gram-negative bacteria may be one of the causative agents. As regards cancer, some studies report an increased risk of stomach cancer and a few studies report an increased risk of cancer in the larynx, liver or, prostate or of leukemia. The spread of the cancers over a multitude of organs does not support a hypothesis of causality with agents commonly found in sewage treatment plants.

CONCLUSIONS

Further investigations are needed to determine the work-related effects and ascertain the causal agents.

Prevalence of antibody to hepatitis A virus in drinking water workers and wastewater workers in Texas from 1996 to 1997

To determine if wastewater workers had a higher prevalence of antibody to hepatitis A virus (anti-HAV) than drinking water workers, a convenience sample of Texas wastewater and drinking water workers was evaluated for risk factors by questionnaire and tested for anti-HAV. A total of 359 wastewater and 89 drinking water workers participated. Anti-HAV positivity was 28.4% for wastewater and 23.6% for drinking water workers. After adjustment for age, educational attainment, and Hispanic ethnicity, the odds ratio for the association between anti-HAV positivity and wastewater industry employment was 2.0 (95% confidence interval, 1.0 to 3.8). Among wastewater workers, never eating in a lunchroom, > or = 8 years in the wastewater industry, never wearing face protection, and skin contact with sewage at least once per day were all significantly associated with anti-HAV positivity in a model that adjusted for age and educational attainment. Wastewater workers in this study had a higher prevalence of anti-HAV than drinking water workers, which suggested that wastewater workers may have been at increased risk of occupationally acquired hepatitis A. Work practices that expose workers to wastewater may increase their risk.

Evaluation of the environmental impact of microbial aerosols generated by wastewater treatment plants utilizing different aeration systems

Using three sampler devices (SAS, Andersen Six-Stages and All Glass Impinger), the environmental impact of bacterial and fungal aerosols generated by municipal wastewater treatment plants operating with different methods of sludge oxygenation were evaluated. The highest microbial concentrations were recovered above the tanks (2247 cfu m-3) and in downwind positions (1425 cfu m-3), where a linear correlation (P < 0.05) was found between the quantity of sewage treated and the entities of microbial aerosol dispersion. Moreover, an exponential increase (P < 0.05) in the bacteria recovered from the air occurred at increasing times of treatment. However, after long-term plant operation, high bacterial and fungal concentrations were found in almost all of the sites around the plant. Coliforms, enterococci, Escherichia coli and staphylococci were almost always recovered in downwind positions. Considerable fractions (20-40%) of sampled bacteria were able to penetrate the final stages of the Andersen apparatus and thus, are likely to be able to penetrate the lungs. The plant operating with a fine bubble diffused air system instead was found to generate rather low concentrations of bacteria and fungi; moreover, staphylococci and indicator micro-organisms were almost absent. Finally, salmonellae, Shigella, Pseudomonas aeruginosa and Aeromonas spp. were not detected in either of the plants. The results indicate a remarkable dispersion of airborne bacteria and fungi from tanks in which oxygen is supplied via a mechanical agitation of sludge, and suggest the need to convert them to diffused aeration systems which pose a lesser hazard for human health.

Seroepidemiology of hepatitis A in Delhi

A prospective study was done to determine the age specific prevalence of antihepatitis A antibodies (anti HAV Abs) among children in Delhi. Four hundred and twenty children aged 0-12 years attending outpatient department for vaccination or any minor illness were studied. Sera was tested by ELISA for anti HAV Abs using a commercial kit (Hepvase A 96 TMB). Thirty samples of cord blood were similarly analyzed. All samples of cord blood were positive for anti HAV Abs. Prevalence of anti HAV Abs was 80% by 5 years of age. The most vulnerable age group was 0.5-1.5 years (anti HAV Ab positivity). Cord blood had 100% positivity. Univariate and multivariate analyses taking anti HAV antibody positivity as dependant variable demonstrated that age and father's education (socioeconomic status) significantly affect prevalence of anti HAV Abs. Sex, water supply, history of jaundice in self or family did not have any significant effect on anti HAV antibody positivity. Prevalence of anti HAV antibodies is 80% by 5 years of age. Further studies in different strata of society and different regions in the country are required to assess the need and age for vaccination.

Evaluation of occupational transmission of hepatitis A virus among wastewater workers

To provide information concerning potential occupational transmission of hepatitis A virus (HAV) among wastewater workers in a large city in the United States, a cross-sectional survey was performed using a saliva test to detect antibodies to HAV (anti-HAV). Fifty-nine (20%) of 302 participants tested positive for anti-HAV. After controlling for the confounding effects of age and race, wastewater work was not significantly associated with an increase in the prevalence of anti-HAV (prevalence ratio = 1.3; 95% confidence interval 0.7 to 2.4). Additionally, when examining only the wastewater workers, no statistically significant occupational risk factors for anti-HAV were identified. The results of this survey are consistent with the position of the Centers for Disease Control and Prevention regarding groups at risk for HAV infection.

Risk of hepatitis A virus infection among sewage workers in Israel

Sewage workers are exposed to a wide range of chemicals and biological agents, including the hepatitis A virus. Inasmuch as Israel is an endemic area for hepatitis A, it is unclear if sewage workers are at increased risk for hepatitis A or which factors contribute to such risk. The authors compared seropositivity of hepatitis A in 100 sewage workers with that in 100 blue-collar worker controls. Hepatitis A seropositivity was highly prevalent, but nonsignificant, in both sewage workers and controls (82% and 91%, respectively). In sewage workers, the major risk for serological positivity was age (odds ratio = 4.5, 95% confidence interval = 1.6, 12.4 for every 10 y). The factors associated negatively with seropositivity were years of education and years of seniority. The authors concluded that exposure to sewage is not a risk factor for hepatitis A infection in Israel, and, therefore, sewage workers do not require special attention in this regard.

Risk of hepatitis A infection in sewage workers

OBJECTIVE

To evaluate the risk of hepatitis A virus (HAV) infection among sewage workers from occupational exposure to raw sewage.

METHODS

An analytical cross sectional study of 241 company employees with possible occupational exposure to sewage in a large water and sewerage company was carried out. Previous exposure to hepatitis A virus infection was assessed, as were its associations with possible risk factors.

RESULTS

Frequent occupational exposure to raw sewage was a significant risk factor for HAV infection, independently of other known risk factors (odds ratio 3.73, 95% confidence interval 1.48 to 9.37). Of 50 employees who reported occupational exposure to raw sewage most of the time, 30 (60%) had had HAV infection.

CONCLUSION

Employees who are likely to be at risk of frequent exposure should have their immunity ensured. The salivary assay for IgG anti-HAV used in the study was highly specific and would be suitable for prevaccination testing of older employees, who are more likely to be immune.

Hepatitis A among workers from a waste water treatment plant during a small community outbreak

OBJECTIVE

This is a case report describing the occurrence of hepatitis A in three workers at a waste water treatment plant during a small community outbreak involving 16 cases.

CASE REPORT

The first case was a 26 year old operator who had worked in the plant for two years, the second was a 23 year old employee hired to add new biolite in the secondary treatment area. These two cases never worked together and only met two or three times before the onset of disease in the second case. The third case occurred three months later in a 34 year old ventilation mechanic. All three cases were confirmed by IgM serology and virus was recovered by polymerase chain reaction in the stools of the last two cases. Despite an extensive search for other risk factors for hepatitis A in these workers none was found.

CONCLUSION

This report confirms that hepatitis A is an occupational hazard for sewage workers. The numerous potential sources of contamination associated with that occupation support the use of vaccine to provide effective prevention.

Seroprevalence of hepatitis A virus infection among sewage workers in the Parisian area, France

Sewers are an ideal environment to be occupationally exposed to viral hepatitis A (HAV) infection, because of high frequency and ability of the virus to remain viable for prolonged periods in sewage. However, data on the occupational risk of HAV infection among sewage workers is not well documented. In a cross sectional study comparing sewage workers (n = 155) to those not occupationally exposed to it (n = 70), we found a non significant increase in HAV seropositivity among sewage workers of 12.9% (p = 0.07). The prevalence of HAV antibody was significantly associated with duration of occupational exposure to sewage (p < 0.015), stay in HAV endemic areas (p < 0.03), age (p < 0.001), and number of siblings (p < 0.03). A stepwise logistic regression analysis gave an adjusted odds ratio for HAV seropositivity 2.15 fold greater in sewage workers compared to those not occupationally exposed to it. So, although there was no significant difference in the prevalence of HAV antibody between sewage workers and others, exposure to sewage was an independent risk factor for HAV seropositivity, and this raises the question of whether it is necessary to vaccinate sewage workers against viral hepatitis A.

Need for vaccination of sewer workers against leptospirosis and hepatitis A

OBJECTIVES

This study compared the prevalence of Leptospira interrogans and hepatitis A virus (HAV) antibodies in serum samples from sewer workers and controls.

METHODS

A blood sample was obtained from 76 of the 101 municipal sewer workers (75%) of Quebec City and from two controls matched to each for age and sex. Testing was done for antibodies against serovars of Leptospira icterohaemorragiae, bratislava, hardjo, grippotyphosa, and kennewicki (pomona) and hepatitis A.

RESULTS

Sewer workers had a greater prevalence of antibodies against leptospirosis than controls (12% v 2%, P = 0.003). In contrast, antibodies to HAV were not significantly more prevalent among workers than among controls (54% v 49%, P = 0.51). Prevalence of HAV antibodies increased significantly with age both among workers and controls (chi 2 for trend, P < 0.001). In contrast with younger workers, prevalence of HAV antibodies was greater among workers > or = 40 years than among their controls (81% v 65%, P = 0.04).

CONCLUSION

Leptospirosis continues to be a problem to sewer workers but hepatitis A is apparently no longer a risk. The likely explanation is that leptospira are still abundant in the sewage system in contrast with HAV, which is only rarely to be found in sewage as a result of the generalised decrease in incidence of hepatitis A in the past three decades. The decision to vaccinate sewer workers against hepatitis A should take into account that it is impossible to avoid all contact with sewage fluid and, despite the fact that the actual incidence of hepatitis A is low, there is a real possibility of sporadic exposure during a future outbreak.