Clinical and diagnostic relevance of the Toxoplasma IgG avidity test in the serological surveillance of pregnant women in Austria

For evaluation of the medical relevance of a Toxoplasma IgG avidity test wi thin the Austrian program for screening of pregnant women, 23 sera from wom en with seroconversions (group 1) and with proven latent Toxoplasma infecti ons (group 3), respectively, as well as 92 sera from women suspected of hav ing a primary infection (group 2) were tested by the indirect immunofluores cence test (IFAT), Sabin-Feldman's dye test (SFT), IgM enzyme-linked immuno fluorescence assay (ELFA-IgM), IgA microparticle enzyme immunoassay, and th e IgG avidity test. Group 1 sera (seroconversions) revealed a median avidit y index (AI) of 0.25, whereas the median AI of group 3 sera (latent infecti ons) was 0.66. In 31 (33.7%) of 92 cases suspected of involving a primary T oxoplasma infection, low (<0.41) or borderline AIs (0.41-0.50) were assesse d, and in 61 cases (66.3%) the AIs exceeded 0.50. Finally, a recent infecti on could be excluded due to the results of the IgG avidity test in 59 cases ; in at least 34 IgM-positive cases an unnecessary and, thus, unjustified t reatment could be avoided.