Assessment of subclinical leprosy infection through the measurement of PGL-1 antibody levels in residents of a former leprosy colony in Thailand.

OBJECTIVES To investigate the hypothesis that there is continuing subclinical M. leprae infection, contributing to ongoing transmission of leprosy in Phra-Pradaeng Colony. DESIGN A sero-epidemiological survey was carried out in Phra-Pradaeng Colony, Thailand between May and August 2005. The clinical and serological examinations were conducted in 398 people, aged 3-84 years (average 50 years), comprising 196 males and 202 females. RESULTS Measurement of serum anti PGL-I antibodies in eligible contacts and ex-patients showed that 18 people (4.5%) were seropositive, six people (1.5%) were strongly positive and 374 people (94.0%) were seronegative. All six people who were strongly seropositive were ex-patients; five of them had no evidence of active leprosy but the sixth person had relapsed BL leprosy with a reversal reaction. CONCLUSIONS This study failed to confirm the hypothesis that there was ongoing subclinical M. leprae infection. More appropriate diagnostic methods and a total survey of the colony should be considered to further clarify this problem.