The first aim of this study was to determine the prevalence of
congenital toxoplasmosis in newborn infants treated by the public health system in Porto Alegre, a city in southern Brazil, using neonatal screening for Toxoplasma gondii-specific
IgM. The second aim was to investigate whether the cases detected by this approach could have been identified by the prenatal screening for
antibodies to T. gondii that was performed in the same population. A fluorometric assay was used to analyse T. gondii-specific
IgM in filter paper specimens obtained from newborn infants for routine screening for
metabolic diseases. When the specific
IgM was positive, serum samples from the infant and the mother were requested for confirmatory serological testing, and the infant underwent clinical examination. Among 10 000 infants screened for T. gondii-specific
IgM, seven filter paper samples were positive, and
congenital toxoplasmosis was confirmed in six patients. The prevalence of
IgM specific for T. gondii was 6/10 000 [95% CI 2/10 000, 13/10 000]. One infected infant had already been identified in the maternity ward before birth, three had been identified by maternal serology at delivery, and two infants with
congenital toxoplasmosis were identified solely through neonatal screening. Although four mothers of the patients with
congenital toxoplasmosis received
prenatal care, and three mothers had one or two serological tests for T. gondii-specific
antibodies (one at first trimester, one at first and second trimesters, and the other at second and third trimesters), they were not identified during pregnancy as infected. Neonatal screening identified cases of
infection not detected by obtaining only one or two serum samples from pregnant women for T. gondii serology, mainly when
infection was acquired and transmitted in late pregnancy. Maternal serology at delivery and neonatal screening were especially useful in the identification of infants with
congenital toxoplasmosis when the mother did not receive regular prenatal serological testing or
prenatal care.