Sibship size as a risk factor for hepatitis A infection.

Marked ethnic differences in the prevalence of anti-hepatitis A antibodies among Jews in Israel are only partly explained by variation in socioeconomic status. In this study, various sociodemographic variables were examined as possible correlates of anti-hepatitis A antibodies in a group of 552 Jewish males aged 25-44 years examined between January and April 1987. Among subjects aged 25-29 years, 41.5% of those of European and American origin had antibodies as compared with 88.5% of those of Asian and North African origin (p less than 0.0001), whereas by the age of 40-44 years, this difference had largely disappeared. In further univariate analysis, number of siblings, years of education, and number of children were also significantly associated with the presence of antibodies. When multiple logistic regression was used to control simultaneously for the effects of the other variables, sibship size emerged as the strongest correlate of anti-hepatitis A antibodies (p less than 0.0001), and it appears to explain a large part of the ethnic differences in antibody status. These findings provide strong evidence for the role of siblings in the spread of hepatitis A infection.