Certainty levels in the diagnosis of leprosy.

This paper describes a procedure for grading the degree of confidence with which it can be held that a diagnosis of leprosy is in fact correct, after considering all available clinical, historical, bacteriological, and histopathological information. Individual suspects are assigned to one of four categories corresponding to different levels of overall certainty of the diagnosis. The method is illustrated using data from the Lepra Evaluation Project in Northern Malawi, and validated in the context of an analysis of BCG's protective efficacy against clinical leprosy. Although the procedures described in this paper were designed for a specific epidemiological study, the method could be adapted for use in most leprosy research or control programs.