Seroprevalence rates of antibodies to phenolic glycolipid-I among school children as an indicator of leprosy endemicity

In order to study whether the seroprevalence of antibodies to phenolic glycolipid-I (PGL-I) among school children is a useful indicator of the leprosy problem in certain areas, school surveys were carried out. These surveys have the advantage of targeting an easily accessible, stable and standardized population. Antibodies to the species-specific PGL-I of Mycobacterium leprae were detected in a simple gelatin particle agglutination test. We have determined the seroprevalence rates in 2835 school children from five different areas in three provinces of Sulawesi, Indonesia. Three areas with a case-detection rate of over 3.4/10,000 were designated as high-endemic areas. The other two were designated as low-endemic areas, having a case-detection rate of less than 1/10,000. The seroprevalence rates in the three high-endemic areas ranged from 26% to 28% (95% CI 21%-31%). In both low-endemic areas the seroprevalence rate was 7% (95% CI 5%-10%). In a second survey conducted in one high-endemic area 3 years after the first survey, the seroprevalence rate was the same as in the first survey. These results indicate that seropositivity rates among school children may reflect the leprosy incidence. They illustrate the potential applicability of seroprevalence as an indicator of the magnitude of the leprosy problem in a selected area.

Patient contact is the major determinant in incident leprosy: implications for future control

Notwithstanding the elimination efforts, leprosy control programs face the problem of many leprosy patients remaining undetected. Leprosy control focuses on early diagnosis through screening of household contacts, although this high-risk group generates only a small proportion of all incident cases. For the remaining incident cases, leprosy control programs have to rely on self-reporting of patients. We explored the extent to which other contact groups contribute to incident leprosy. We examined retrospectively incident leprosy over 25 years in a high-endemic village of 2283 inhabitants in Sulawesi, Indonesia, by systematically reviewing data obtained from the local program and actively gathering data through interviews and a house-to-house survey. We investigated the contact status in the past of every incident case. In addition to household contact, we distinguished neighbor and social contacts. Of the 101 incident cases over a 25-year period, 79 (78%) could be associated to contact with another leprosy patient. Twenty-eight (28%) of these 101 cases were identified as household contacts, 36 (36%) as neighbors, and the remaining 15 (15%) as social contacts. Three patients had not had a traceable previous contact with another leprosy patient, and no information could be gathered from 19 patients. The median span of time from the registration of the primary case to that of the secondary case was 3 years; 95% of the secondary cases were detected within 6 years after the primary case. The estimated risk for leprosy was about nine times higher in households of patients and four times higher in direct neighboring houses of patients compared to households that had had no such contact with patients. The highest risk of leprosy was associated with households of multibacillary patients. The risk of leprosy for households of paucibacillary patients was similar to the risk of leprosy for direct neighboring houses of multibacillary patients, indicating that both the type of leprosy of the primary case and the distance to the primary case are important contributing factors for the risk of leprosy. Contact with a leprosy patient is the major determinant in incident leprosy; the type of contact is not limited to household relationships but also includes neighbor and social relationships. This finding can be translated into a valuable and sustainable tool for leprosy control programs and elimination campaigns by focusing case detection and health promotion activities not only on household contacts but also on at least the neighbors of leprosy cases.