A serological survey for cholear antibodies in rural east Pakistan. 1. The distribution of antibody in the control population of a cholera-vaccine field-trial area and the relation of antibody titre to the pattern of endemic cholera.

Controlled cholera vaccine field trials were held in Matlab Bazar in rural East Pakistan in 1963 and 1964. In July-September 1965, a serological survey for cholera antibodies was carried out on a random sample of the field-trial population. Results are given for the control group only, as representative of the pattern found in an endemic cholera area. Only 2% of the blood samples from children under 10 years of age were found to have detectable agglutinating antibody (titres of 1:20 or more), while the proportion in the age-group over 30 years was 27%-30%. Tests for vibriocidal antibody showed that none of the blood samples from children under 1 year of age contained detectable antibody, while 87%-90% of those from adults over 30 years did so. The rise in the geometric mean vibriocidal titre showed an almost linear correlation with a sharp fall in the cholera case rate with age. Since a similar survey in a non-endemic area (Czechoslovakia) did not reveal any rise in antibody titre with age, and since cholera epidemics in areas without recent experience of the disease are characterized by a higher incidence rate in adults than in children, it is suggested that the antibody titres give a measure of the level of immunity in a population.