Epidemiological studies of Hepatitis A in Singapore.

1,341 cases of Hepatitis A were reported during the 44-month period between January 1977 and August 1980. The morbidity rate per 100,000 population varied from 9.4 in 1977 to 25.2 for the first eight months of 1980. The case fatality rate was 1.0%. Among the three major ethnic groups, Indians had the highest morbidity rate; but during outbreaks, the attack rate was highest among the Chinese. High age-specific morbidity rate was noted in the 15-34 years age group. The male to female ratio was 2.9: 1. 7.4% of the cases contracted the disease overseas while 7.2% gave a contact history with known hepatitis cases. Contact with unrecognised asymptomatic or mild cases in the community could probably be the mode of transmission for a considerable proportion of the reported cases. Ingestion of raw or partially cooked imported bivalve molluscs (cockles and oysters) was associated with an outbreak in September 1978 and the outbreaks in 1980. The possibility of low-level transmission by water should be seriously considered.