A village outbreak of hepatitis A: acquaintance network and inapparent pre-school transmission compared.

A village outbreak of 38 cases of serologically confirmed hepatitis A is described. The epidemic curve was a propagative one and all of the cases occurred in primary school-age or pre-school children. In 1984 the incidence in this age group was 5,000 per 100,000, about 50 times the corresponding national rate. Although 21 of the cases attended the single primary school, these cases were not clustered within school years or classes and examination of onset dates showed only four cases could have resulted from case transmission within classes. A matched triplet case-control study was undertaken to measure the risk associated with prior contact with a case within the acquaintance network and the risk of household contact with either of the two pre-school nurseries where inapparent transmission may have been occurring. Whereas a similar proportion of cases and controls had direct or indirect contact with the nurseries, 48% of cases, compared with 9% of controls, reported a previous case of jaundice within 6 weeks amongst their acquaintance network (matched triplet analysis P less than .0001).