The association between responses to an inquiry about contact with triatomid bugs and the confirmation of infection by complement fixation test is examined in a group of 2.154 cases from a hospital blood bank. The laboratory examination revealed a prevalence of infection of 14,5% and the inquiry a positive contact history of 11,5%. However, positive findings for both methods coincided in only 2,5%, while negative findings coincidedin 76,5%. The total concordance of findings, or the efficacy of the inquiry to correctly indicate the State of infection, was 79%. The sensitivity of the screening instrument was low (17,3%) and the specificity high (89,5%). The predictive value of a positive history of contact was only 21,5%, while that of a negative history was 86,5%. These results indicate that inquiries carried out in this way are of little value in screening for Chagas'disease and should be discontinued in blood banks, unless their precision can be enhanced.
Chagas' disease; Screening; Epidemiologic evaluation