Leprosy in Louisiana, 1855-1970. An epidemiologic study of long-term trends.

Study of a well known focus of leprosy in Louisiana in 1855-1970 showed a decrease in incidence which began before the use of chemotherapy. Many of the cases had onset in a limited area of Louisiana, French Louisiana, where there was a high incidence of multiple family cases. Overall incidence rates were found to be decreasing for each cohort of birth, and within cohorts after 1920, the highest incidence rates were in the age group 10-19. A high incidence rate was found for cases with onset in the years 1900-1929; rather than an epidemic, this was probably related to bias in the recording of year of onset. Although persistent for a long period, the focus remained limited in geographic extent and seems to be disappearing.