IgM enzyme-linked immunosorbent assay test for the diagnosis of congenital Toxoplasma infection.

An IgM enzyme-linked immunosorbent assay, developed for detection of IgM antibodies to Toxoplasma gondii, was evaluated to define its usefulness for diagnosis of congenital Toxoplasma infection. Sera from 51 infants suspected of having congenital Toxoplasma infection but in whom this diagnosis was ruled out were negative in the IgM-ELISA test. Fifty of them were also negative in the IgM-fluorescent antibody test; the one which was positive was from an infant with congenital syphilis who had circulating rheumatoid factor. Of 55 sera from newborn infants with proved congenital Toxoplasma infection, the IgM-ELISA test was positive in 43 (72.7%), whereas the IgM-IFA test was positive in only 14 (25.4%). Of those sera obtained during the first 30 days of life the infected infants, 81.2% were positive in the IgM-ELISA test, whereas only 25% were positive in the IgM-IFA test. The Igm-ELISA test avoids the false-positive results owing to RF and the false-negative results owing to competition from high levels of maternal IgG antibody which occur in the IgM-IFA test. We conclude that the IgM-ELISA test is highly sensitive and specific for diagnosis of congenital Toxoplasma infection.