Immunoglobulin M-immunosorbent agglutination assay for diagnosis of infectious diseases: diagnosis of acute congenital and acquired Toxoplasma infections

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Abstract
An IgM immunosorbent agglutination assay (IgM-ISAGA) was negative in all sera from individuals negative in the Sabin-Feldman dye test, in sera from individuals with chronic Toxoplasma infection, and in cord blood samples from uninfected infants. In contrast, all sera that were obtained from individuals with a recent history of acute Toxoplasma infection and from infants with congenital Toxoplasma infection and that were positive in both the dye test and the IgM-indirect fluorescent-antibody (IgM-IFA) test were positive in IgM-ISAGA. A total of 21 (67.7%) of 31 sera that were negative in the IgM-IFA test, despite being obtained from individuals with recently acquired Toxoplasma infection, and 8 (72.7%) of 11 sera that were negative in the IgM-IFA test and obtained from infants with congenital Toxoplasma infection were positive in IgM-ISAGA. The presence of rheumatoid factor, antinuclear antibodies or both did not cause false-positive results in the IgM-ISAGA but did so in the IgM-IFA test. IgM-ISAGA is both more sensitive and more specific than the IgM-IFA test for detection of IgM antibodies to T. gondii and for the diagnosis of acute congenital and acquired Toxoplasma infections.