[Hepatitis A outbreak with arca as the vehicle of transmission].

An outbreak of hepatitis A occurred during the period from January 20th to April 30 1988 in Ningbo City. 47,313 patients were reported and four patients died. Morbidity rate was 949.78 per 1,000,000 and fatality rate was 0.08 per 1,000. The positivity rate of anti-HAV IgM in the patient's sera was 95.55%. The history of eating Arca was 82.56% among the patients. Retrospective cohort studies showed that the morbidity of the residents who had eaten Arca was 8.53%, and that of the residents who had not eaten Arca was 0.77%. The difference was highly significant (P less than 0.01, chi 2 = 39.49, RR = 11.08). The attributable risk percent (AR%) of the resident eating Arca was 90.97%. HAV and HAV RNA have been observed in the body of Arca bought from Qidong County, Jiangsu Province, bred in the seashore of Ningbo City for 59 days, by the method of tissue-culture and DNA hybridization assay.