Vibriocidal titre in cholera cases and contacts: its value in assessing endemicity of or susceptibility to cholera.

Vibriocidal antibody titre in excess of 1:40 occurred within two weeks of cholera infection, both in severe hospitalized cases, contact cases and in asymptomatic infected contacts. These levels, considered to be indicative of protection, persisted for six months or longer in more than half of the subjects irrespective of presence and severity of symptoms. Approximately 40% of infected family contacts had similar titres implying recent infection and subsequent protection. The use of antibiotics to treat acute cases, and whether infection was due to antibiotic resistant or sensitive Vibrio cholerae had no effect on the response of vibriocidal titre. Endemicity of cholera was higher than previously observed in Dhaka. Screening populations to obtain positive titre rates permits retrospective assessment of cholera infection and provides an indicator of future susceptibility.