Subclinical infection with Mycobacterium leprae--a problem for leprosy control strategies.

Tests for the serodiagnosis of leprosy, including those based on phenolic glycolipid-I (PGL-I), have shown poor specificity for leprosy in studies of endemic communities, despite initially promising results in studies of selected patients. During a 5 years follow-up study of a hyperendemic community in Papua New Guinea, a marked reduction in numbers of seropositive children and an increase in age of those seropositive followed introduction of multi-drug therapy. This was accompanied by a reduced case detection rate and a shift to paucibacillary disease in new cases, consistent with a reduction in transmission. Only a minority of persistently seropositive persons developed leprosy. These observations suggest that subclinical infection with Mycobacterium leprae is common in endemic communities and that PGL-I seropositivity is a marker of subclinical infection, with poor specificity for overt disease. Detection of subclinical infection may confound control strategies which use screening tests to identify asymptomatic highly infectious cases for earlier therapy.