RESUMO
Data from the late eighties indicate that 1.6% of the Mexican population was infected with Chagas' disease and that transmission by way of blood transfusion was taking place in nearly every state, in areas of different sizes. The risk of transmission via that route has seldom been documented in Mexico, and for this reason a sentinel survey was conducted in 1994 in 18 blood banks belonging to the Ministry of Health and located in various states. The purpose of the study was to determine the risk of transmission via blood transfusion and to calculate the national prevalence of infection among potential donors, so as to have a set of general indicators of the prevailing disease burden and of the importance of this transmission route. Participants were selected on the basis of operating criteria: all government-run transfusion centers with the capacity to screen blood donors for at least one year and persons seeking to donate blood (n = 64,969) who satisfied the Official Mexican Standards (Norma Official Mexicana) for the therapeutic use of human blood and blood products. For the analysis of the results the centers were grouped according to migration flow in order to detect any possible influence the latter may have had on Chagas' disease transmission within the country. Screening was done with indirect hemagglutination using a reagent produced by the Instituto Nacional de Diagnóstico y Referencia Epidemiológicos and donated to the blood banks. Positive cases were confirmed by indirect immunofluorescence. Positive results were detected in 996 persons, for a prevalence of 1.5% (95% CI: 1.44 to 1.63). Concordance between the final results obtained by local labs and by the central lab was given by a kappa index of 0.87 (95% CI: 0.862 to 0.877). Cities having the highest emigration rates had three times the risk of transmission as compared to cities that drew immigrants (odds ratio = 2.82; 95% CI: 2.18 to 3.65). We recommend that mandatory serologic screening be enforced throughout Mexico, since migration makes it difficult to determine which areas are endemic.
