Serum tests for the diagnosis of Leprosy using Phenolic GlicoLipid-1 (PGL-1), considered a specific antigen for M. leprae, have opened some possibilities for studying the epidemiological behavior of this disease. Some questions, such as incubation period, sub-clinical infection and the importance of household contacts for endemic control, have been better evaluated using this technique. The present study has the objective of verifying a possible association between the serological status and the occurrence of leprosy. The authors performed a 4-year follow-up of 6,520 individuals, all of them 5 years old or over, submitted to a PGL-1 ELISA test at the beginning of the study. The group was part of the universe of 7,416 inhabitants of the urban area of a highly endemic town of the State of São Paulo. The serological research identified 590 positive individuals (9.0%). Within this time period, 82 new cases were detected, 26 among the serum positive group (441/10,000), 48 among negatives (81/10,000) and 8 (89/10,000) among those who had not been tested. The analysis of results attempted to control for household contact status, considering that the standardized seropositive rate by age and sex was 9.61% in the contact group, and 7.64% in the non-contact group. The group of serum negatives and no household contact, the so called "non- exposure group", was adopted as reference to compute the relative risk to develop leprosy within the study period. Detection rates were standardized considering age differences between the groups and the results were: seropositive household contact rate was 1,074/10,000, that is, 27 times higher than in the "non-exposure group" (63/10,000). The detection rate in the seropositive non-household contact group was 274/10,000 and in the seronegative household contact group 198/10,000, both higher than the rate in the "non-exposure group" but similar between each other. The serum positive condition accounted for an 8.6 times higher leprosy risk in the contact group and for a 4.4 times higher risk in the non-contact group. In the epidemiological situation of this research, a highly endemic leprosy area, 50% of the new cases were in the non-contact seronegative group, that is, those whose infection source was unknown. So, in practice, the test revealed itself to be of little usefulness. Anti-PGL-1 serology in low and medium leprosy prevalence areas still remains to be studied in order to reach more solid conclusions on its use in leprosy control. On the other hand, further serologic and other studies are recommended in order to improve the identification of sub-clinical infection, paucibacilar forms included, so as to expand the possibility of early diagnosis and effective influence on the endemic behavior of the disease.
leprosy; anti-PGL-1 test; leprosy epidemiology; cohort study; leprosy detection rate; household contacts; leprosy serum test
