Nested case-control study in a serological survey to evaluate the effectiveness of a Chagas disease control programme in Brazil

Objective To identify risk factors associated with Trypanosoma cruzi infect ions in areas under surveillance in the State of Minas Gerais, Brazil. Methods A model using a nested case-control design incorporated within a se rological survey of schoolchildren which was employed to evaluate the effec tiveness of the Chagas disease control programme. Findings In a sample of 40 374 schoolchildren (aged 7-14 years) surveyed, 1 6 children tested positive for T. cruzi antibody (by indirect immunofluores cence and indirect haemagglutination). In the case-control study, each case was randomly matched to three seronegative controls (classroom and age +/- 1 year). Compared to controls, T: cruzi-seropositive children were more li kely to have a seropositive mother (odds ratio (OR) = 6.8; 95% confidence i nterval (CI) = 0.71-63.9) or a seropositive family member (OR = 8.6; 95% CI = 1.0-75.5). Conclusion Use of the nested case-control model in a sero-epidemiological s urvey to evaluate risk factors for T cruzi transmission was adequate for as sessing the effectiveness of a Chagas disease control programme.