Negligible prevalence of antibodies against Trypanosoma cruzi among blood donors in the southeastern United States.

Trypanosoma cruzi, a hemoflagellate, causes Chagas' disease and is endemic throughout Latin America. Increasing Latin American immigration to the United States has enhanced concern about transmission of Chagas' disease by infected donor blood. The insect vector and parasites also have been found in the southeastern United States. Autochthonous infection of several species of wild and domesticated mammals suggests that the general human population also may be at risk. To assess the prevalence of antibodies to T cruzi in humans, randomly selected donor blood was screened. Initial screening was performed by indirect hemagglutination (1:4 initial serum dilution) and at least one of three different enzyme immunoassays. All samples testing positive by at least one screening method were tested by radioimmunoprecipitation and indirect immunofluorescence supplemental methods, which were used for confirmation and calculation of specificity. Of the 6,013 serum samples evaluated, 85 tested positive by one screening method. Only 10 of the samples tested positive by more than one method. The percentages of positive screening tests are 0.05% by indirect hemagglutination and 0.06%, 0.91%, 3.97% by Abbott Laboratories (Abbott Park, Ill), Gull (Gull Laboratories, Salt Lake City, Utah), and Polychaco (Polychaco S.A.I.C., Buenos Aires, Argentina) enzyme immunoassays, respectively. All samples were negative by radioimmunoprecipitation and indirect immunofluorescence. These results suggest that although parasite and vector are found in the southeastern United States and both infect mammals, the risk of natural infection to humans in this region seems to be negligible. There was variation in positivity among different screening methods. The highest percentage of positive results was with the enzyme immunoassay, in which the binding of serum antibodies to antigens is amplified by enzymatic reactions.