[Serological diagnosis of congenital infection with Trypanosoma cruzi]

Enzyme linked immuno sorbent assay (ELISA) for IgG and IgM antibodies against T. cruzi were applied to 382 sera form adults and newborn infants, referred to our laboratory for serological diagnosis, to improve diagnosis of congenital Chagas disease. A comparative study between immunofluorescent antibody test (IFAT) and ELISA results was undertaken for IgG T. cruzi antibodies in 346 samples of adults sera, 225 of which were IFAT negative (non reactive or reactive at dilutions under 1/10) and 121 IFAT IgG positive (reactive at dilutions > or = 1/20). Positive results were obtained with both methods in 117 patients, only with ELISA in 11 IFAT negative samples and only with IFAT at low titers in four ELISA IgG negative (non reactive or reactive in dilutions < or = 1/40) samples. Thus ELISA IgG did not detect more infections than IFAT IgG, although ELISA showed higher titers (> or = 2 dilutions) in 42/117 simultaneously positive specimens. In 88 sera from patients with acute, chronic and initial infection, ELISA-IgM rendered more positive results than IFAT-IgM, including approximately 17% of low titers false positives in control's sera. For this reason, when such results are obtained in patient's sera, it is advisable to consider them suspicious and to repeat the test in order to get a definitive result. ELISA allowed to detect IgM in sera from four of 36 infants born to infected mothers, which had given negative results with IFAT IgM. These results confirm that ELISA is more sensitive than IFAT for IgM antibodies.(ABSTRACT TRUNCATED AT 250 WORDS)