Endemicity and epidemicity of cholera.

In this review of the factors governing the endemicity and epidemicity of cholera, special attention is paid to attempts to demarcate endemic areas by statistical methods, in particular by the use of Swaroop's "index of endemicity". Once such areas are delineated, it is possible to assess the characteristic features-such as the presence of numerous water tanks, the heavy pollution of water in the dry season, and socio-cultural factors-which help to maintain continuity of infection.While some of the causes underlying epidemic outbreaks of cholera are still obscure, it is clear that these outbreaks derive in large part from the introduction of infection into communities whose members have no immunity (or have lost their immunity) to cholera, and that a very important role is played here by movements of groups of the population-particularly, in India, the movement of pilgrims and others to and from fairs and festivals.