Socioeconomic, environmental, and behavioural risk factors for leprosy in North-east Brazil: results of a case-control study

Background Brazil reports almost 80% of all leprosy cases in the Americas. This study aimed to identify socioeconomic, environmental, and behavioural factors associated with risk of leprosy occurrence in the endemic North-eastern region. Methods A case-control study in four municipalities. Cases: cases of leprosy diagnosed in the previous 2 years, with no other known, current, or past case of leprosy in the household or in the neighbourhood. Controls: individuals presenting for reasons other than skin problems to the health unit where the case was diagnosed and who lived in the same municipality as the case with whom it was matched. For each case four controls were selected. A semi-structured questionnaire was used to collect demographic, socioeconomic, environmental, and behavioural data. A multivariate hierarchical analysis was performed according to a previously defined framework. Results 226 cases and 857 controls were examined. Low education level, ever having experienced food shortage, bathing weekly in open water bodies (creek, river and/ or lake) 10 years previously, and a low frequency of changing bed linen or hammock (,biweekly) currently were all significantly associated with leprosy. Having a BCG vaccination scar was found to be a highly significant protective factor. Conclusions Except for BCG vaccination, variables that remained significant in the hierarchical analysis are cultural or linked to poverty. They may act on different levels of the transmission of Mycobacterium leprae and/or the progress from infection to disease. These findings give credit to the hypothesis that person-to-person is not the only form of M. leprae transmission, and that indirect transmission might occur, and other reservoirs should exist outside the human body.