DETECTION OF ANTIBODIES TO TRYPANOSOMA-CRUZI AMONG BLOOD-DONORS IN THE SOUTHWESTERN AND WESTERN UNITED-STATES .2. EVALUATION OF A SUPPLEMENTAL ENZYME-IMMUNOASSAY AND RADIOIMMUNOPRECIPITATION ASSAY FOR CONFIRMATION OF SEROREACTIVITY

Background: Chagas' disease, caused by the protozoan parasite Trypanos oma cruzi, is endemic to Latin America and may be transmitted in the U nited States via blood donated by infected immigrants. Blood-borne pat hogens such as T: cruzi require supplemental testing for confirmation of seroreactivity. Study Design and Methods: A study was undertaken to determine an optimal scheme for confirmation of seroreactivity in rep eatedly reactive samples identified by the Chagas antibody enzyme immu noassay (EIA). The procedure for initial confirmation involves three p urified antigens coated onto three separate polystyrene beads and uses an EIA format. If the sample is reactive with two of three or three o f three antigens, it is confirmed as seroreactive. If none or one of t hree beads is reactive, the sample is indeterminate and subjected to a radioimmunoprecipitation assay (RIPA), The RIPA must demonstrate char acteristic bands at 32, 34, and 90 kDa. Results: When tested with sera from persons with potentially cross-reactive diseases (n = 39) or aga inst a presumed negative population from southeast Wisconsin (n = 289) , the confirmatory EIA had a specificity of 100 percent. Sensitivity w as 100 percent (28/28) with xenodiagnosis-positive sera and 97.6 perce nt (80/82) with chagasic sera from Latin America. The RIPA showed a sp ecificity of 100 percent in EIA-nonreactive samples (n = 100) and a se nsitivity of 100 percent with both xenodiagnosis-positive (28/28) and chagasic (82/82) sera. Conclusion: The confirmatory EIA and the RIPA t ogether provide a highly specific and sensitive means of confirming se roreactivity for antibodies to T. cruzi.