RESUMEN
INTRODUCTION: Leprosy household contact investigation has been recommended as an epidemiological surveillance strategy for more than 50 years. OBJECTIVE: 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. METHODS: 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. RESULTS: 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. CONCLUSION: The lost cases due to insufficient contact investigation represent lost opportunities in early detection and treatment, thus losing the opportunity to reduce leprosy transmission.