The goal of this study was to investigate the importance of
IgG avidity testing in newborns (NBs) diagnosed with early
congenital toxoplasmosis. We collected samples from 88 puerperae infected by Toxoplasma gondii (T. gondii) and their NBs (48 acutely-infected puerperae (AIP) and 40 chronically-infected puerperae (CIP)), from two public maternity hospitals in Goiania city, Goias, Brazil, from 2010 to 2015. Specific
anti-T. gondii
IgM and
IgG serum levels and
IgG avidity tests were evaluated using chemiluminescence.
Congenital toxoplasmosis was observed in 66.66% (n = 32) of NBs with AIP, 94.1% presenting low avidity (LA) and 51.61% presenting high avidity (HA) test results. The
IgG and
IgM levels of NBs with LA and their puerperae were higher in comparison with HA NBs and puerperae (p = 0.0001). The avidity tests showed 100% specificity and 50% sensitivity (p = 0.0001). NBs with LA had a 15-fold increased risk of developing
congenital toxoplasmosis in comparison with HA NBs. The
IgG avidity test could be used to assist in early
congenital toxoplasmosis diagnoses in NBs and LA, identifying a greater probability of vertical transmission.