Discrepancies in the Diagnosis of Congenital Toxoplasma gondii Infection Between B1 Gene Semi-Nested Polymerase Chain Reaction and Serological Analyses

Congenital <i>Toxoplasma gondii</i> (<i>T. gondii</i>) infection, which can be caused by a primary <i>T. gondii</i> infection during pregnancy, results in severe neurological sequelae in affected children. We have been conducting a prospective cohort study since January 2019 on pregnant women who were suspected of having primary <i>T. gondii</i> infection based on serological tests. In this study, congenital infection was diagnosed using semi-nested polymerase chain reaction (PCR) to detect the B1 gene in the body fluids of newborns. Up until December 2023, forty-one newborns born to mothers suspected of having primary <i>T. gondii</i> infection during pregnancy underwent B1 gene semi-nested PCR tests and anti-<i>T. gondii</i> immunoglobulin (Ig) G and IgM measurements of their blood samples. Eight newborns showed no clinical symptoms of congenital <i>T. gondii</i> infection; however, they were diagnosed with congenital <i>T. gondii</i> infection according to positive PCR results. However, none of the eight infants eventually exhibited any sign of congenital infection, as their serum samples tested negative for anti-<i>T. gondii</i> IgM and IgG until 12 months of age. Therefore, clinicians should consider discrepancies in the diagnosis of congenital <i>T. gondii</i> infection between PCR tests using body fluids of newborns and serological tests during their infantile period.