Transmission of Hansen's disease and unscreened household contacts

Leprosy household contact investigation has been recommended as an epidemiological surveillance strategy for more than 50 years.

The purpose of this study was to estimate the yield that could be achieved in case detection if four contacts could be examined for every case found.

For the estimation of the number of cases not detected (lost) and yield per contact investigation in Mato Grosso, the incidence rates and yield calculations from a cohort study conducted in Rio de Janeiro by Matos et al (1999) were applied to data from the state of Mato Grosso. Also, to identify high-risk groups for leprosy, a cross-sectional study was conducted in which leprosy cases found as a result of a contact investigation were compared with index cases detected by other means.

The lost cases among household contacts were at least 4 per every 10 new cases detected. This is the result of insufficient contact investigations--it being 0.8 instead of 4 contact investigations per each case as recommended by the Brazilian Ministry of Health. Up to 60% of the incidence of leprosy could be explained by the high number of lost cases among household contacts not examined. Women and children are more likely to be contacts.

The lost cases due to insufficient contact investigation represent lost opportunities in early detection and treatment, thus losing the opportunity to reduce leprosy transmission.