Diagnosis of Congenital Toxoplasmosis: Performance of Four IgG and IgM Automated Assays at Birth in a Tricentric Evaluation

For postnatal diagnosis of congenital toxoplasmosis (CT), the gold standard for the detection of anti-Toxoplasma IgM in newborns relies on the immunosorbent agglutination assay (ISAGA), which is manufactured from whole Toxoplasma parasites that become difficult to maintain. For IgG, only the Platelia assay provides a validated assay for cord blood according to the manufacturer, allowing its use in this context. We compared the analytical performance of four commercialized automated assays, Platelia, Abbott, Vidas, and Liaison, for the detection of IgG and IgM in the cord blood or peripheral blood of newborns from women infected during pregnancy. The assays were performed on samples from 509 newborns, collected from the university hospitals of Montpellier, Nimes, and Toulouse. For IgM, the four assays appeared to be sufficiently informative to be used for congenital toxoplasmosis diagnosis (area under the curve [AUC] > 0.8, receiver operating characteristic [ROC] analysis), with Platelia showing the best performance, similar to ISAGA with regard to accuracy (83%). For the Vidas (76%), Abbott (75%), and Liaison (74%) assays, the accuracy was significantly lower. Maternal treatment significantly decreased the sensitivity of all the assays. For IgG, the four evaluated assays showed a sensitivity of over 90%, with Abbott (95%) and Liaison (94%), exhibiting a significantly higher sensitivity than Platelia (90%). Furthermore, Abbott showed its superiority in the cases of maternal infection during the third trimester. In the context of the newborns of mothers infected by Toxoplasma gondii during pregnancy, to ensure efficient care, Platelia and Abbott seemed to be the most suitable reference tests for the detection of IgM for the former and IgG for the latter.