An epidemic of hepatitis A related to ingestion of raw oysters.

An epidemic of hepatitis A occurred around Hondo City, Kumamoto Prefecture in Japan during the first six months of 1982. Clinical, immunological and epidemiological studies were carried out in 225 cases. Cases were distributed over a relatively wide area, and in small numbers of young children and school children. More than half of the patients were in their twenties or thirties. The clinical course was generally favorable with rapid resolution. No episode lasted more than six months. There was only one fatality in a cure which was a carrier of HBs antigen with liver cirrhosis. Titers of IgM anti-HAV measured by radioimmunoassay (RIA) or enzyme immunoassay (EIA) reached a peak during the second week after onset, followed by a gradual decrease. Conversion to negative results was never experienced within two months. We found a good correlation between RIA and EIA in terms of detecting IgM anti-HAV. The route of infection was thought to be fecal-oral in nature, with ingestion of raw oysters the major etiologic factor.