The relationship of vibriocidal antibody titre to susceptibility to cholera in family contacts of cholera patients.

A bacteriological and serological study of family contacts of 81 cholera patients was carried out in Dacca, East Pakistan. In the 10-day follow-up, 78 (16.7%) of 466 contacts were found to be infected with Vibrio cholerae; half of them were symptomatic and 29 had to be admitted to hospital. A study of serum pairs revealed a 4-fold, or greater, rise in titre in 86% of those infected in whom diarrhoea was present, and in 77% of individuals with inapparent infections. The infection rate fell markedly with age. Serological tests for vibriocidal antibody on blood specimens collected at the initiation of the follow-up revealed higher titres with increasing age. Vibrio cholerae infection, whether symptomatic or asymptomatic, predominantly occurred in individuals with low titres.