Leprosy incidence: six years follow-up of a population cohort in Bangladesh

Background: With approximately 250,000 new leprosy cases detected annually, transmission of M. leprae appears to be ongoing in many areas of the world. By studying prospectively the number of leprosy patients found in a population sample at the beginning of the study (prevalence) and the number of new patients found during the 6-year observation period (incidence), we aim to understand better the transmission of M. leprae and the burden of disease. Methodology: To establish the prevalence and incidence rates of leprosy in the general population of a high endemic area in Bangladesh, we followed prospectively 20,218 individuals from a random cluster sample of the population and examined them at 2-yearly intervals for 6 years. Results: At intake we found 27 new leprosy cases, indicating a prevalence of previously undiagnosed leprosy of 13·3/10,000. Follow-up at 2, 4 and 6 years revealed 17, 16, and eight new cases, respectively, representing incidence rates of 4.0, 4·5 and 2·3/10,000 PYAR, respectively. The incidence rate over 6 years was 3·7/10,000 PYAR. The observed incidence rate is three times higher than the new case detection rate in the same area. Of all 68 new leprosy cases, five (7%) had MB leprosy. The proportion of children under 15 years was 24%. The proportion of female patients was 60%, but the incidence rate of leprosy was the same for males and females. Conclusions: The decline in incidence of leprosy in a general population sample is less pronounced than routine data from a control programme led us to expect.