HOUSEHOLD AND DWELLING CONTACT AS RISK-FACTORS FOR LEPROSY IN NORTHERN MALAWI

Data on household and dwelling contact with known leprosy cases were a vailable on more than 80,000 initially disease-free individuals follow ed up during the 1980s in a rural district of northern Malawi. A total of 331 new cases of leprosy were diagnosed among them, Individuals re corded as living in household or dwelling contact with multibacillary patients at the start of follow-up were at approximately five- to eigh tfold increased risk of leprosy, respectively, compared with individua ls not living in such households or dwellings. Individuals living in h ousehold or dwelling contact with paucibacillary cases were both at ap proximately twofold increased risk. The higher risk associated with mu ltibacillary contact and the fact that dwelling contact entailed a gre ater risk than household contact if the association was with multibaci llary, but not with paucibacillary, disease suggest that paucibacillar y cases may not themselves be sources of transmission, but rather just markers that a household has had contact with some (outside) source o f infection. When household contact was considered alone, the risks of disease were appreciably higher for younger than for older contacts a nd for male compared with female contacts. Despite the elevated risk o f leprosy associated with household or dwelling contact, only 15% of a ll incidence cases arose among recognized household contacts. Given th e dynamic nature of household membership and consequent misclassificat ion of contact status, the true contribution to overall incidence of c ontact within household or dwelling settings is likely to be much high er than this, perhaps 30% or higher, Considering the predilection of m ales for infectious multibacillary forms of the disease, the transmiss ion of Mycobacterium leprae at an early age, in particular to males, m ay be of particular importance for the persistence of leprosy in endem ic communities. Although residential contact with a multibacillary cas e is the strongest known determinant of leprosy risk, the vast majorit y of such contacts never manifest disease, which indicates a crucial r ole for genetic and/or environmental factors in the transmission of M. leprae infection and/or the pathogenesis of clinical leprosy.