Seroepidemiological study on 724 household contacts of leprosy patients in French Polynesia using disaccharide-octyl-BSA as antigen.

A seroepidemiological surveillance of a contact population was started in 1984 in French Polynesia. The ELISA test was used to measure IgM anti-ND-O-BSA in the sera. Specific antibody levels were higher in healthy Polynesians than in normal individuals living in a nonendemic country. The positive threshold of the reaction was fixed according to this background activity in healthy Polynesians. Under these conditions, 100% of the multibacillary patients were detected as seropositive as compared to 5% of the paucibacillary group. In the population of 724 household contacts tested and observed for 2 years: 93 (12.8%) were seropositive, with 8 (1.1%) showing activity equivalent to multibacillary patients (1 of these 8 individuals developed a lepromatous form of leprosy); 631 (87%) were seronegative and 3 developed a paucibacillary form of the disease (2 BT, 1 I) without any antibody increase. Among those four contacts who developed leprosy, three were related to a multibacillary index case. These data suggest that this test may be useful for the prediction of multibacillary leprosy. A long-term surveillance of this high-risk population will be able to evaluate the diagnostic and prognostic value of the serological assay.