A virologically studied epidemic of type A hepatitis in a school for the mentally retarded.

The occurrence of hepatitis A virus (HAV) infection in a small boarding school for mildly to moderately mentally retarded children in Umka, Yugoslavia, in the spring of 1979, six years after the last recognized occurrence, provided an opportunity to study the spread of the agent among 79 classroom and dormitory contacts. Only 51% of those who had entered subsequent to the prior outbreak had detectable antibody (anti-HAV) with immunoglobulin G predominance, and the proportion within the first six years of training did not vary. Both findings suggest a lack of endemicity during the interval. The outbreak ended spontaneously just before the summer vacation with an anti-HAV prevalence of 90%. The ratio of silent to overt cases was approximately 2:1. HAV was found in fecal samples from susceptible residents with inapparent infection as well as those with hepatitis. Among those with prior experience, there were no significant anti-HAV increases to suggest HAV reinfection in this group. Overall, 32% were seropositive for markers of past or chronic hepatitis B virus (HBV) infection, but this status did not correlate with sex, year of training, or HAV experience. Only one instance of HBV transmission was observed in the same interval as the 26 HAV infections.