An epidemic of epidemic hepatitis occurred in the district of a rural Central School in Yates and Ontario Counties of Central New York. The epidemic comprised 176 cases of which 135 were jaundiced, and extended from September 1949 to May 1950, with most cases in March 1950. No common source could be demonstrated and the transmission was believed to be due to human contact alone. The overall morbidity rate was about 5%, attack rate among school children 22%, and among the adults and pre-school family contacts of infected school children the attack rate was 18%, with no significant age difference in attack rate. Differences in attack rate in the various school grades were explained by higher number of siblings of children in certain grades. Household attack rates among non-school persons were related to number of sick school children, family size, and hygienic standard of the home. The first of these factors seemed most important. More jaundiced cases occurred in families where the exposure was heaviest
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