Epidemiology of a cluster of Henoch-Schönlein purpura.

We investigated a case cluster of Henoch-Schönlein purpura that occurred in Connecticut during the fall and winter of 1987-1988. In Hartford County, where the case finding was most complete, 16 children were identified with disease onset during the 7-month cluster period (incidence, 1.7 cases per 10,000 children per year) compared with only 3 children with disease onset during the preceding 7 months. The incidence in Hartford County was higher among urban (4.8/10,000) and Hispanic (8.6/10,000) children and children in lower socioeconomic groups (6.9/10,000) than among suburban children or children in higher socioeconomic or different racial groups (0.9 to 1.1 per 10,000). We performed a case-control study involving 14 of the 16 case children from Hartford County, 10 case children from nearby areas, and 47 control children matched to the case children by age and race. Case children were more likely than control children to have had a sore throat during the month before the onset of Henoch-Schönlein purpura (52% vs 22%; odds ratio, 3.8; 95% confidence interval, 1.1 to 13). This difference and other smaller differences between case and control children suggest that the cluster may have been caused by person-to-person spread of an infectious agent of the respiratory tract to susceptible hosts. To our knowledge this is the first report of a cluster of Henoch-Schönlein purpura, and it provides clues for a better understanding of the etiology and epidemiology of the disease.