Presence and duration of anti‐Toxoplasma gondii immunoglobulin M in infants with congenital toxoplasmosis

Objectives: to investigate the rate of positivity for immunoglobulin M anti‐Toxoplasma gondii (Toxo‐IgM) in newborns with congenital toxoplasmosis, and the age when these antibodies become negative. Methods: patients with congenital toxoplasmosis who started monitoring in a congenital infection clinic between 1998 and 2009 were included. Inclusion criteria were routine maternal or neonatal serological screening; diagnostic confirmation by persistence of immunoglobulin G anti‐Toxoplasma gondii at age ≥ 12 months, and Toxo‐IgM screening in the neonatal period. To calculate the frequency of positive Toxo‐IgM, cases detected by neonatal screening were excluded. For the study of the age when Toxo‐IgM results became negative, patients with negative Toxo‐IgM since birth and those in whom it was not possible to identify the month when the negative result was achieved were excluded. Results: among the 28 patients identified through maternal screening, 23 newborns had positive Toxo‐IgM (82.1%, 95% CI: 64.7‐93.1%). When adding the 37 patients identified by neonatal screening, Toxo‐IgM was positive in the first month of life in 60 patients, and it was possible to identify when the result became negative in 51 of them. In 19.6% of patients, these antibodies were already negative at 30 days of life; and in 54.9%, at 90 days. Among the 65 patients included in the study, 40 (61.5%) had some clinical alteration. Conclusions: even with high sensitivity methods, newborns with congenital toxoplasmosis can have negative Toxo‐IgM at birth. In those who have these antibodies, the positive period may be quite short. It is important not to interrupt the monitoring of infants with suspected congenital toxoplasmosis simply because they present a negative Toxo‐IgM result