GEOGRAPHIC DETERMINANTS OF LEPROSY IN KARONGA DISTRICT, NORTHERN MALAWI

Background. Geographical differences in leprosy risk are not understoo d, but may provide clues about the natural history of the disease. We report an analysis of the geographical distribution of leprosy in Karo nga District, a rural area of Northern Malawi, between 1979 and 1989. Methods. Cohort study of the incidence of leprosy based on two total p opulation surveys. Area of residence was determined using aerial photo graphs, which allowed identification of households, as well as locatio n of roads, rivers and the lake shore. Results. Incidence rates were b etween two and three times higher in the north compared to the south o f the district, and lowest in the semi-urban district capital. The mos t obvious environmental difference between these regions is the north' s higher rainfall and more fertile soil. There was no overall associat ion between leprosy incidence and population density, although highest rates were observed in the least densely populated areas. Looking at the entire district, incidence rates increased with increasing distanc e from a main road, but declined with increasing distance from a river or from the shore of Lake Malawi. The negative association with proxi mity to rivers may reflect the larger number of rivers in the north of the district. Apparent differences in incidence rates between groups speaking different languages reflected confounding by area of residenc e. Conclusions. There is a marked variation, not explained by socioeco nomic or cultural factors, in the incidence of leprosy within Karonga District. Our results are consistent with a theme in the literature as sociating the environment, particularly proximity to water, with lepro sy.