Leprosy in Malawi. 1. Sensitivity and specificity of the diagnosis and the search for risk factors for leprosy.

The sensitivity and specificity of the diagnosis of leprosy in the context of a total population survey are examined. It is apparent that diagnostic tools are unsatisfactory with regard to reaching a highly sensitive and specific case definition of paucibacillary leprosy, particularly in actively found suspects. Histopathological examination of 4 mm punch biopsy specimens contributed appreciably to both the sensitivity and specificity of the diagnosis of leprosy, though there was evidence for false positive and false negative histopathology results. The needs for high sensitivity during the intake phase of a vaccine trial and for high specificity during follow-up surveys for risk factors are discussed.