Leprosy case detection rates by age, sex, and polar type under leprosy control conditions.

The knowledge of leprosy epidemiology is still extremely limited as to basic epidemiologic characteristics. Only the infectious agent and the reservoir of infection have been firmly established. It is all the more surprising that very few studies of analytical leprosy epidemiology are reported in the literature. In order to contribute to the analysis of these characteristics, data are presented on the age and sex distribution of types of leprosy from the Pogiri Leprosy Control Project, a large leprosy control project in Andhra Pradesh, India. This data base includes records on biannual examination of some 160,000 household contacts of nearly 48,000 leprosy cases observed from five to nine years between 1962 and 1970. These data indicate a peak of leprosy prevalence and incidence in the age group 35-44 years. The sex differential in leprosy, observed in these data, appears more related to sex differences in social contact, as sex ratios of leprosy vary widely among different populations. Finally, the age distribution of tuberculoid leprosy shows a bimodal curve, with peaks at ages 10-14 and 35-44 years. The first peak appears related both to the occurrence of early and self-healing lesions in school children, and to the more frequent examination of school children. Additional observations are presented on type ratios of leprosy in single and multiple case households, and on per cent of single lesions for tuberculoid cases detected over time.