Will we miss specific IgA detection for the diagnosis of congenital toxoplasmosis? A French retrospective monocenter study on 483 infants.

To estimate the performance of anti-Toxoplasma IgA assay for the diagnosis of congenital toxoplasmosis, a retrospective monocenter study was conducted comparing serological results obtained in the framework of routine diagnosis workup. All infants born to mothers infected with Toxoplasma gondii during pregnancy from 2010 to 2023 with at least 6 months of serological follow-up were included. Four hundred and eighty-three cases (1,171 sera) were included, of which 56 infants (11.6%) were infected. Twenty out of 60 infants (33.3%) with positive IgA were not infected. The sensitivity to detect IgA antibodies in infected neonates was 71.4%. The specificity was 97.3%. The mean time to detect IgA was 7.7 ± 13.0 days in infected neonates. Anti-Toxoplasma IgA was the earliest positive serological test in only two cases (5.0%) but turned negative at 1 month in the absence of specific treatment, suggesting non-specific detection. IgA was associated with anti-Toxoplasma IgM, neosynthetized IgG or IgM on comparative Western blotting (WB), or both IgM and neosynthetized IgG or IgM on WB, in 12 cases (30.0%), 2 cases (5.0%), and 19 cases (47.5%), respectively. Sixteen infants with no IgA after birth were diagnosed via neosynthetized IgG or IgM on comparative WB and/or IgM (n = 10), or via PCR on amniotic fluid (n = 5), or persistent IgG (n = 1). Our study suggests that anti-Toxoplasma IgA is not a critical serological parameter for the diagnosis of congenital toxoplasmosis, and the recent withdrawal of commercialized reference anti-Toxoplasma IgA assays should not affect patient care.IMPORTANCEThis study will help clinical microbiologists estimate the impact of the withdrawal of anti-Toxoplasma IgA reference assays for the diagnosis of congenital toxoplasmosis and will contribute to actualize the recommendations for laboratory diagnosis.