Hepatitis A as an occupational hazard Friedrich Hofmann*, Gudrun Wehrle, Hans Berthold and Dorothea K6ster* Few studies have been carried out to evaluate the role o[hepatitis A virus (HA V) as an occupational hazard. Our analysis of data on occupational diseases in German), showed that hepatitis A ranks as third among &fectious occupational diseases. Morbidio, based on the frequency o f compensation (15.2%) was in the same range as that observed/or hepatitis B (19.7%). In another stud),, data were collected on anti-HA V prevalence among 2293 hospital workers in southwest Germany. Anti-HA V prevalence o[ hospital staff responsible for patient care and that of the general population were comparable, while food-handlers under the age 0./'30 years had a higher degree of anti-HA V prevalence. When an evaluation of anti-HA V prevalence data was carried out on persons younger than 30 years who comprised subsets of the medical stqffl the relative risk was: charwomen 4.2, food-handlers 2.49, and paediatric nurses 1.84, showing that they had higher prevalence rates than nurses 1.25, physicians 1.09 and laboratory assistants 0.93. Vaccinations for the prevention of hepatitis A should therefore reach individuals that have an increased occupational risk. food-handlers, health care workers in infectious diseases and paediatrics, medical staff in laboratories handling stool samples, medical charwomen and, according to previously published work, staff of day care centres and sewerage workers. Keywords: Hepatitis A: occupationalrisk: food-handlers:charwomen: medicalpersonnel
INTRODUCTION Hepatitis A immunity in industrialized countries has decreased significantly since the end of the Second World War t.2. While several studies have evaluated the hepatitis A risk of travellers and soldiers, few reports have discussed this disease in the context of an occupational health problem. Lange and Masihi 3 found that physicians in paediatric units had a higher degree of immunity (38%) than their colleagues in other (adult) departments. Almost 12% of nurses younger than 25 years working in general medical departments had antibodies to hepatitis A virus (anti-HAV-positive) while 15% of nurses in paediatric stations had antibodies. As no differentiation between staff from high endemic (e.g. southern Europe) and low endemic regions (e.g. Germany) was investigated, the true occupational risk could not be derived from reported data. Flehmig 4 reported 4% anti-HAV-positive persons among 1600 people working at Tfibingen University Hospital without evaluation of occupational risk in the different professions. Abdo et al5,6measured anti-HAV in different occupational groups in Cologne (Germany) and compared results with the degree of immunity found among the normal population. The percentage of anti-HAV-positive
Department of Occupational Health, University Hospital, Breisacher Str. 60, D W-7800 Freiburg, Germany. *Occupational Health service of the Reutlingen County, D W-7410 Reutlingen, Germany. tTo whom correspondence should be addressed
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Vaccine, Vol. 10, Suppl. 1, 1992
persons among sewerage workers younger than thirty years (9%) was in the same range as the results obtained from the normal population (8.6%). Sewerage workers over 30 years of age, however, showed a strikingly higher rate of anti-HAV reactions (30.7%). The authors regarded this evolving spread of infection as a result of continuous occupational contact with HAV-contaminated sewage sediment. Similiar risks were obtained for the staff of day-care centres, where 26.6% of persons younger than 30 years were positive. The rate of antiHAV-positive persons in the staff of geriatric wards (8.6%) was identical to that of the normal population. Data are presented on the role of hepatitis A as an occupational disease in (West) Germany. The second part deals with data on HAV-seroprevalence among > 2000 persons in medical and non-medical professions of four southwest German hospitals. MATERIALS AND METHODS Data on the role of hepatitis A as an occupational disease were obtained in collaboration with the BGW (Berufsgenossenschaft ftir Gesundheitsdienst und Wohlfahrtspflege Federal German Occupational Insurance, Hamburg, FRG). An analysis was performed to find the most important occupational diseases with special regard to infectious conditions and the frequency of compensation, presumably based on the severity of the disease. The second study was of 2293 persons working in the University Hospital of Freiburg and three hospitals of Reutlingen County (near Stuttgart). Sera were collected 0264-410X/92/100S82-03 © 1992Butterworth-HeinemannLtd
Hepatitis A and occupational health." F. Hofmann et al. Dermatoses 73.596
Hepatitis B 70.9~
Hepatitis A 15.8~ o n a r y disease 9.2~ O t h e r diseases 10.1~
Hepatitis n o n - A n o n - B
I n f e c t i o u s disease 7.3~
13.3~
Figure 1 Reported occupational diseases of West German health-care staff (n = 8398). The data are given as a percentage of all occupational diseases reported to the Berufsgenossenschaff for Gesundheitsdienst und Wohlfahrtspflege (Federal German Occupational Insurance, Hamburg) in 1990
a
Hepatitis B
during routine occupational health check-ups and were tested by a radioimmunoassay (RIA) technique (HAVAB, Abbott Laboratorics, USA). The sample was divided into five groups: foreigners from Southern Europe working in food-handling and the medical professions, German personnel employed in food-handling and the medical professions, and German personnel working in non-medical professions (general population).
74.7~
Hepatitis A 15.1Y,
Hepatitis n o n - A n o n - B 10.2~
RESULTS
b
Hepatitis A as an occupational disease In 1990, 8398 diseases of suspected occupational origin in West German health-care staff were reported to the BGW. Of these, 7.3 % were concerned with infectious disease (Figure 1). In the same year, 978 individuals received compensation for their occupational diseases. The fact that 32.3% of these cases (n = 316) were of infectious origin reflects the important role that bacterial and viral diseases play in health care. Of the 305 reported occupational hepatitis cases in 1989, 15.1% were caused by HAV, a frequency similar to that observed in 1984 (Figure 2). Analysis of the occupational disease data collected from 1984 to 1990 showed that the decrease seen in hepatitis A infections was similar to that observed for all infectious occupational diseases. Among the 305 occupational hepatitis cases reported in 1989, the compensation frequency for hepatitis A (15.2%) was almost the same as that found for hepatitis B (19.7%) and indicated that one out of seven HAV infections was severe (Figure 3). Southwest German anti-HAV-prevalenee study In the course of the southwest German anti-HAVprevalence study, 2040 Germans and 253 south Europeans, mostly from Spain, Italy and Croatia, were tested for hepatitis A immunity. The overall prevalence of antiHAV among foreigners was 58.2%. Kitchen and catering staff had a higher degree of immunity than medical professionals (Table 1). Determination of hepatitis A immunity among 2040 persons working in different medical and non-medical professions is summarized in Table 2. The overall antiHAV prevalence in staff from medical departments was comparable to that of the general population. Foodhandlers, under the age of 30 years (including appren-
Figure 2
Occupational hepatitis cases reported in 1984 (a) and 1989 (b) by West-German health-care staff by etiology. (a) n = 533; (b) n = 305
50 38.7
4O
>.
30 2O
19.7 15.2
LL
0
Hepatitis A
- -
Hepatitis B
Hepatitis non-A non-B
Figure 3 Compensation frequency of hepatitis cases reported as occupational diseases to the Berufsgenossenschaft fiir Gesundheitsdienst und Wohlfahrtspflege (Hamburg) in 1989.
Table 1 Immunity to HAV by age group in 64 medical and 789 kitchen personnel from southern European countries
HAV immunity (%) Age group (years)
Medical staff
Kitchen staff
< 30 30-40 > 40
57 94 76
80 91 91
Vaccine, Vol. 10, Suppl. 1, 1992
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Hepatitis A a n d o c c u p a t i o n a l health." F, H o f m a n n et al. Table 2 Immunity to HAV by age group in 1445 medical and 348 kitchen personnel from Germany compared to 247 individuals from the general population HIV immunity (%) Group
Apprentices/ students
Charwomen NA Laboratory 2.1 assistants Nurses 2.2 Paediatric nurses 0 Physicians 3.7 Staff from 2.5 medical departments Foodhandlers 7.5 General population NA
< 30 years
30-40 years
> 40 years
18.5 4.0
40.0 13.0
67.3 56.0
5.5
35.2
63.6
8.1 4.8 4.3
25.0 17.2 24.5
55.2 44.4 60.5
10.7
35.8
62.5
4.4
35.7
71.2
NA, Not applicable
Laboratory assistants~
0.93
Geriatric n u r s e s ~ 1 Sewage w o r k e r s ~
a I .01 a
Physicians ~ Nu rses
I ,09
ii iiiil i ~ i!i!11.2 s
Paediatric nurses 1.84 Foodhandlers i!!!!!!i! iii! !ii ilii!ii!i!!!i! i !!!!:::]2.49 Staff, day-care:::::::::::::i::!:::::!::!:i::i:ii::::::::::::::::: 3.1 a cen tres iii ?iiii iiii?ii ii i iiiii ii iii i ii iiiiiiiiiii'.. .....
Sewerage workersiiiiiiiiiiiiii::!::!:i::i::i:i::i::::::il :!::i:: ::::::::[4" 0
1
2
3
g
hospital and health-care stall e.g. foodhandlers, c h a r w o and paediatric nurses. In view of these results, it should be considered whether the occupational differences alone account for the divergence in immunity between the groups or whether socioeconomic aspects and differences in the standard o f hygiene are also responsible for H A V infections. The data published by Richards 7 and the findings o f Sobsey el als on survival and persistence o f H A V in environmental samples support the observations o f Dienstag et a l ? , Papaevangelou et al. ~" and Yao ~ that H A V infection is possible via contaminated food and kitchen staff. The relative risk t'or hepatitis A in sewerage workers, calculated from the data given by A b d o and Chriske (4.15), is almost the same as the rate found in medical charwomen in this study (4.2). This illustrates the occupational risk caused by exposure to stool. The differences in a n t i - H A V prevalence tk~und for nurses in other departments and paediatric nurses (relative risk o f 1.25 and 1.84, respectively) support the importance o f H A V transmission by' the faecal oral route. Conversely, the difference between paediatric nurses and medical c h a r w o m e n (relative risk of 1.84 and 4.2, respectively) may not be explained by occupational risks alone. Socioeconomic factors, standards of hygiene and travel habits, which might account for the difference seen in hepatitis A immunity between these two groups, should be investigated further. men
REFERENCES
15a
1 5
Relative r i s k Figure 4 Relative risk of HAV-immunity in German persons under 30 years of age working in different at-risk hospital professions compared to the general population
tices) had higher prevalence rates than medical department staff overall and the general population. When the data obtained from the medical department staff were broken down further, it could be demonstrated that charwomen had the highest prevalence rates in each age group. As prevalence rates among personnel in the two older age groups (30-40 years and > 40 years) might reflect a 'historical risk' caused by poor hygienic standards existing in Germany after the Second World War, it was decided to calculate the relative risk for the different occupations among persons younger than 30 years. The ratio of prevalence in each subset compared to the general population was used to express relative risk. As shown in Figure 4, the relative risk varied from 0.93 in laboratory assistants to 4.20 among medical charwomen.
2
3 4
5
6
7
8
9
10
DISCUSSION The results of our study show that hepatitis A is an important hazard to health care workers. The fact that compensation rates for hepatitis A are comparable to those of hepatitis B indicates that the importance of hepatitis A might often be underestimated. Therefore, not only should travellers be vaccinated, but also certain
S84
Vaccine, Vol. 10, Suppl. 1, 1992
11
Flehmig, B., Pfister, H. and Heinrichs, U. Immunogenicity of a killed hepatitis A vaccine in seronegative volunteers. Lancet 1989, i, 10391041 Weiland, O., Berg, J., Back, E. and Lundbergh, P. Immunoglobulin prophylaxis against hepatitis A among Swedish UNO soldiers in an endemic region. Infection 1979, 7, 223-225 Lange, W. and Masihi, KN. Zur Epidemiologie der Hepatitis A in Berlin (West). Bundesgesundheitsblatt 1982, 29, 183-187 Flehmig, B. Stand der Hepatitis-A-Impfstoffentwicklung. In: Arbeitsmedizin im Gesundheitedienst Vol. 3, (Eds Hofmann, F. and StSBel, U.) Gentner Verlag, Stuttgart, 1989, pp. 89-95 Abdo, R. und Chriske, H. HAV-Infektionsrisiken im Krankenhaus, Altenheim und Kindertagesst~.tten. In: Arbeitsmedizin im GesundheitsdienstVol. 5, (Eds Hofmann, F. and StSBel, U.) Gentner Verlag, Stuttgart, 1990, pp. 143-147 Chriske, H., Abdo, R., Richrath, R. and Braumann, S. Hepatitis-AInfektionsgefgthrdung bei Kanal- und Kla.rwerksarbeitern. Arbeitsmedizin im Offentlichen Dienst, Tagungsbericht Gentner Verlag, Stuttgart, 1990, pp. 159-172 Richards, G.P. Outbreaks of shellfish-associated enteric virus illness in the United States. Requisite for development of viral guidelines. J. Food Protect 1985, 48, 815-623 Sobsey, M., Shields, P., Hauchman, F., Davis, A., Rullman, V. and Bosch, A. Survival and persistence of hepatitis A virus in environmental samples. In: Viral Hepatitis and Liver Disease (Ed. Zuckerman, A.J.) Alan R. Liss, New York, 1988, pp. 121-124 Dienstag, J., Routenberg, J., Purcell, R., Hooper, R. and Harrison, W. Foodhandler-associated outbreak of hepatitis type A. Ann. Intern. Med. 1975, 8,3, 647-650 Papaevangelou, G., Biziagos,E., Stathpopoulos, G., Crance, J., Vayona, T. and Deloince, R. Detection of hepatitis A virus from shellfish and seawater: one-year study in Thermaicos Gulf (ThessaIoniki, Greece). In: Viral Hepatitis and Liver Disease (Eds Hellinger, F.B., Lemon, S.M. and Margolis, H.) Williams & Wilkins, Baltimore, 1991, pp. 78431 Yao, G. Clinical spectrum and natural history of viral hepatitis A in a 1988 Shanghai Epidemic. In: Viral Hepatitis and Liver Disease (Eds Hollinger, F.B., Lemon, S.M and Margolis, H.) Williams & Wilkins, Baltimore, 1991, pp. 76-78
INTRODUCTION Hepatitis A immunity in industrialized countries has decreased significantly since the end of the Second World War t.2. While several studies have evaluated the hepatitis A risk of travellers and soldiers, few reports have discussed this disease in the context of an occupational health problem. Lange and Masihi 3 found that physicians in paediatric units had a higher degree of immunity (38%) than their colleagues in other (adult) departments. Almost 12% of nurses younger than 25 years working in general medical departments had antibodies to hepatitis A virus (anti-HAV-positive) while 15% of nurses in paediatric stations had antibodies. As no differentiation between staff from high endemic (e.g. southern Europe) and low endemic regions (e.g. Germany) was investigated, the true occupational risk could not be derived from reported data. Flehmig 4 reported 4% anti-HAV-positive persons among 1600 people working at Tfibingen University Hospital without evaluation of occupational risk in the different professions. Abdo et al5,6measured anti-HAV in different occupational groups in Cologne (Germany) and compared results with the degree of immunity found among the normal population. The percentage of anti-HAV-positive
Department of Occupational Health, University Hospital, Breisacher Str. 60, D W-7800 Freiburg, Germany. *Occupational Health service of the Reutlingen County, D W-7410 Reutlingen, Germany. tTo whom correspondence should be addressed
$82
Vaccine, Vol. 10, Suppl. 1, 1992
persons among sewerage workers younger than thirty years (9%) was in the same range as the results obtained from the normal population (8.6%). Sewerage workers over 30 years of age, however, showed a strikingly higher rate of anti-HAV reactions (30.7%). The authors regarded this evolving spread of infection as a result of continuous occupational contact with HAV-contaminated sewage sediment. Similiar risks were obtained for the staff of day-care centres, where 26.6% of persons younger than 30 years were positive. The rate of antiHAV-positive persons in the staff of geriatric wards (8.6%) was identical to that of the normal population. Data are presented on the role of hepatitis A as an occupational disease in (West) Germany. The second part deals with data on HAV-seroprevalence among > 2000 persons in medical and non-medical professions of four southwest German hospitals. MATERIALS AND METHODS Data on the role of hepatitis A as an occupational disease were obtained in collaboration with the BGW (Berufsgenossenschaft ftir Gesundheitsdienst und Wohlfahrtspflege Federal German Occupational Insurance, Hamburg, FRG). An analysis was performed to find the most important occupational diseases with special regard to infectious conditions and the frequency of compensation, presumably based on the severity of the disease. The second study was of 2293 persons working in the University Hospital of Freiburg and three hospitals of Reutlingen County (near Stuttgart). Sera were collected 0264-410X/92/100S82-03 © 1992Butterworth-HeinemannLtd
Hepatitis A and occupational health." F. Hofmann et al. Dermatoses 73.596
Hepatitis B 70.9~
Hepatitis A 15.8~ o n a r y disease 9.2~ O t h e r diseases 10.1~
Hepatitis n o n - A n o n - B
I n f e c t i o u s disease 7.3~
13.3~
Figure 1 Reported occupational diseases of West German health-care staff (n = 8398). The data are given as a percentage of all occupational diseases reported to the Berufsgenossenschaff for Gesundheitsdienst und Wohlfahrtspflege (Federal German Occupational Insurance, Hamburg) in 1990
a
Hepatitis B
during routine occupational health check-ups and were tested by a radioimmunoassay (RIA) technique (HAVAB, Abbott Laboratorics, USA). The sample was divided into five groups: foreigners from Southern Europe working in food-handling and the medical professions, German personnel employed in food-handling and the medical professions, and German personnel working in non-medical professions (general population).
74.7~
Hepatitis A 15.1Y,
Hepatitis n o n - A n o n - B 10.2~
RESULTS
b
Hepatitis A as an occupational disease In 1990, 8398 diseases of suspected occupational origin in West German health-care staff were reported to the BGW. Of these, 7.3 % were concerned with infectious disease (Figure 1). In the same year, 978 individuals received compensation for their occupational diseases. The fact that 32.3% of these cases (n = 316) were of infectious origin reflects the important role that bacterial and viral diseases play in health care. Of the 305 reported occupational hepatitis cases in 1989, 15.1% were caused by HAV, a frequency similar to that observed in 1984 (Figure 2). Analysis of the occupational disease data collected from 1984 to 1990 showed that the decrease seen in hepatitis A infections was similar to that observed for all infectious occupational diseases. Among the 305 occupational hepatitis cases reported in 1989, the compensation frequency for hepatitis A (15.2%) was almost the same as that found for hepatitis B (19.7%) and indicated that one out of seven HAV infections was severe (Figure 3). Southwest German anti-HAV-prevalenee study In the course of the southwest German anti-HAVprevalence study, 2040 Germans and 253 south Europeans, mostly from Spain, Italy and Croatia, were tested for hepatitis A immunity. The overall prevalence of antiHAV among foreigners was 58.2%. Kitchen and catering staff had a higher degree of immunity than medical professionals (Table 1). Determination of hepatitis A immunity among 2040 persons working in different medical and non-medical professions is summarized in Table 2. The overall antiHAV prevalence in staff from medical departments was comparable to that of the general population. Foodhandlers, under the age of 30 years (including appren-
Figure 2
Occupational hepatitis cases reported in 1984 (a) and 1989 (b) by West-German health-care staff by etiology. (a) n = 533; (b) n = 305
50 38.7
4O
>.
30 2O
19.7 15.2
LL
0
Hepatitis A
- -
Hepatitis B
Hepatitis non-A non-B
Figure 3 Compensation frequency of hepatitis cases reported as occupational diseases to the Berufsgenossenschaft fiir Gesundheitsdienst und Wohlfahrtspflege (Hamburg) in 1989.
Table 1 Immunity to HAV by age group in 64 medical and 789 kitchen personnel from southern European countries
HAV immunity (%) Age group (years)
Medical staff
Kitchen staff
< 30 30-40 > 40
57 94 76
80 91 91
Vaccine, Vol. 10, Suppl. 1, 1992
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Hepatitis A a n d o c c u p a t i o n a l health." F, H o f m a n n et al. Table 2 Immunity to HAV by age group in 1445 medical and 348 kitchen personnel from Germany compared to 247 individuals from the general population HIV immunity (%) Group
Apprentices/ students
Charwomen NA Laboratory 2.1 assistants Nurses 2.2 Paediatric nurses 0 Physicians 3.7 Staff from 2.5 medical departments Foodhandlers 7.5 General population NA
< 30 years
30-40 years
> 40 years
18.5 4.0
40.0 13.0
67.3 56.0
5.5
35.2
63.6
8.1 4.8 4.3
25.0 17.2 24.5
55.2 44.4 60.5
10.7
35.8
62.5
4.4
35.7
71.2
NA, Not applicable
Laboratory assistants~
0.93
Geriatric n u r s e s ~ 1 Sewage w o r k e r s ~
a I .01 a
Physicians ~ Nu rses
I ,09
ii iiiil i ~ i!i!11.2 s
Paediatric nurses 1.84 Foodhandlers i!!!!!!i! iii! !ii ilii!ii!i!!!i! i !!!!:::]2.49 Staff, day-care:::::::::::::i::!:::::!::!:i::i:ii::::::::::::::::: 3.1 a cen tres iii ?iiii iiii?ii ii i iiiii ii iii i ii iiiiiiiiiii'.. .....
Sewerage workersiiiiiiiiiiiiii::!::!:i::i::i:i::i::::::il :!::i:: ::::::::[4" 0
1
2
3
g
hospital and health-care stall e.g. foodhandlers, c h a r w o and paediatric nurses. In view of these results, it should be considered whether the occupational differences alone account for the divergence in immunity between the groups or whether socioeconomic aspects and differences in the standard o f hygiene are also responsible for H A V infections. The data published by Richards 7 and the findings o f Sobsey el als on survival and persistence o f H A V in environmental samples support the observations o f Dienstag et a l ? , Papaevangelou et al. ~" and Yao ~ that H A V infection is possible via contaminated food and kitchen staff. The relative risk t'or hepatitis A in sewerage workers, calculated from the data given by A b d o and Chriske (4.15), is almost the same as the rate found in medical charwomen in this study (4.2). This illustrates the occupational risk caused by exposure to stool. The differences in a n t i - H A V prevalence tk~und for nurses in other departments and paediatric nurses (relative risk o f 1.25 and 1.84, respectively) support the importance o f H A V transmission by' the faecal oral route. Conversely, the difference between paediatric nurses and medical c h a r w o m e n (relative risk of 1.84 and 4.2, respectively) may not be explained by occupational risks alone. Socioeconomic factors, standards of hygiene and travel habits, which might account for the difference seen in hepatitis A immunity between these two groups, should be investigated further. men
REFERENCES
15a
1 5
Relative r i s k Figure 4 Relative risk of HAV-immunity in German persons under 30 years of age working in different at-risk hospital professions compared to the general population
tices) had higher prevalence rates than medical department staff overall and the general population. When the data obtained from the medical department staff were broken down further, it could be demonstrated that charwomen had the highest prevalence rates in each age group. As prevalence rates among personnel in the two older age groups (30-40 years and > 40 years) might reflect a 'historical risk' caused by poor hygienic standards existing in Germany after the Second World War, it was decided to calculate the relative risk for the different occupations among persons younger than 30 years. The ratio of prevalence in each subset compared to the general population was used to express relative risk. As shown in Figure 4, the relative risk varied from 0.93 in laboratory assistants to 4.20 among medical charwomen.
2
3 4
5
6
7
8
9
10
DISCUSSION The results of our study show that hepatitis A is an important hazard to health care workers. The fact that compensation rates for hepatitis A are comparable to those of hepatitis B indicates that the importance of hepatitis A might often be underestimated. Therefore, not only should travellers be vaccinated, but also certain
S84
Vaccine, Vol. 10, Suppl. 1, 1992
11
Flehmig, B., Pfister, H. and Heinrichs, U. Immunogenicity of a killed hepatitis A vaccine in seronegative volunteers. Lancet 1989, i, 10391041 Weiland, O., Berg, J., Back, E. and Lundbergh, P. Immunoglobulin prophylaxis against hepatitis A among Swedish UNO soldiers in an endemic region. Infection 1979, 7, 223-225 Lange, W. and Masihi, KN. Zur Epidemiologie der Hepatitis A in Berlin (West). Bundesgesundheitsblatt 1982, 29, 183-187 Flehmig, B. Stand der Hepatitis-A-Impfstoffentwicklung. In: Arbeitsmedizin im Gesundheitedienst Vol. 3, (Eds Hofmann, F. and StSBel, U.) Gentner Verlag, Stuttgart, 1989, pp. 89-95 Abdo, R. und Chriske, H. HAV-Infektionsrisiken im Krankenhaus, Altenheim und Kindertagesst~.tten. In: Arbeitsmedizin im GesundheitsdienstVol. 5, (Eds Hofmann, F. and StSBel, U.) Gentner Verlag, Stuttgart, 1990, pp. 143-147 Chriske, H., Abdo, R., Richrath, R. and Braumann, S. Hepatitis-AInfektionsgefgthrdung bei Kanal- und Kla.rwerksarbeitern. Arbeitsmedizin im Offentlichen Dienst, Tagungsbericht Gentner Verlag, Stuttgart, 1990, pp. 159-172 Richards, G.P. Outbreaks of shellfish-associated enteric virus illness in the United States. Requisite for development of viral guidelines. J. Food Protect 1985, 48, 815-623 Sobsey, M., Shields, P., Hauchman, F., Davis, A., Rullman, V. and Bosch, A. Survival and persistence of hepatitis A virus in environmental samples. In: Viral Hepatitis and Liver Disease (Ed. Zuckerman, A.J.) Alan R. Liss, New York, 1988, pp. 121-124 Dienstag, J., Routenberg, J., Purcell, R., Hooper, R. and Harrison, W. Foodhandler-associated outbreak of hepatitis type A. Ann. Intern. Med. 1975, 8,3, 647-650 Papaevangelou, G., Biziagos,E., Stathpopoulos, G., Crance, J., Vayona, T. and Deloince, R. Detection of hepatitis A virus from shellfish and seawater: one-year study in Thermaicos Gulf (ThessaIoniki, Greece). In: Viral Hepatitis and Liver Disease (Eds Hellinger, F.B., Lemon, S.M. and Margolis, H.) Williams & Wilkins, Baltimore, 1991, pp. 78431 Yao, G. Clinical spectrum and natural history of viral hepatitis A in a 1988 Shanghai Epidemic. In: Viral Hepatitis and Liver Disease (Eds Hollinger, F.B., Lemon, S.M and Margolis, H.) Williams & Wilkins, Baltimore, 1991, pp. 76-78
