Anti-PGL-I seroepidemiology in leprosy cases: household contacts and school children from a hyperendemic municipality of the Brazilian Amazon

[[[ Objective: ]]] We investigated the prevalence of antibodies against PGL-I in people affected by leprosy (PAL) who were diagnosed and treated between 2004 and 2010, their household contacts (HC) and school children (SC) from a hyperendemic municipality in the Brazilian Amazon, and determined the prevalence of previously undiagnosed leprosy (PPUL) among both the HC and SC. [[[ Design: ]]] We conducted a cross-sectional study involving 87 PAL, 302 HC and 188 SC. The subjects were clinically assessed, and their levels of anti-PGL-I antibodies were determined by ELISA. The subjects were also interviewed to determine their demographic and socio-economic characteristics. [[[ Results: ]]] For PAL, a mean of 44 (SD = 21.8) months had passed since their initial diagnosis, and 34 (39%) of them remained seropositive. The level of anti-PGL-I antibodies was significantly higher in multibacillary (MB) than in paucibacillary (PB) cases (P < 0.05). Thirty-nine percent of HC were positive for anti-PGL-I, and we detected eight (2.6%) new cases among these individuals. One hundred and twenty-five SC (66.5%) were seropositive, and we detected nine (4.8%) new cases of leprosy (eight PB and one MB) in this group. When we visited the homes of SC affected by leprosy, 31 contacts were clinically examined, and three (10%) new cases were detected (one PB and two MB). The mean age of students with leprosy was 14.1 years (SD = 2.5; min = 10, max = 18). [[[ Conclusion: ]]] The seroepidemiology of anti-PGL-I and the PPUL among both HC and SC suggests that there are many active foci of infection and that Mycobacterium leprae is circulating among this population.