An enzyme-linked immunosorbent assay for detection of IgM antibodies to Toxoplasma gondii: use for diagnosis of acute acquired toxoplasmosis.

In an enzyme-linked immunosorbent assay (ELISA) for detection of IgM antibodies to Toxoplasma gondii, sera from individuals with negative results in the Sabin-Feldman dye test (DT) and sera from individuals with chronic toxoplasma infection all yielded negative results, even when tested undiluted. In contrast, of sera obtained from individuals with recently acquired toxoplasmosis, all sera that gave positive results in both the DT and the IgM-immunofluorescent antibody (IgM-IFA) test and 92.8% of sera that gave negative results in the IgM-IFA test yielded strongly positive results in the IgM-ELISA. Thus, the IgM-ELISA is more sensitive than the IgM-IFA test in the diagnosis of recently acquired infection with T. gondii. Moreover, sera that gave negative results in the DT but that contained either antinuclear antibodies or rheumatoid factor and thus caused false-positive results in the IgM-IFA test all yielded negative results in the IgM-ELISA, probably because serum IgM and IgG fractions were separated during the initial step.