Serological evidence of Toxoplasma gondii infection among pregnant women in Auckland.

Aim: Severe congenital infection is a consequence of primary Toxoplasma gondii infection in early pregnancy. Antenatal screening is problematic because IgM antibody to Toxoplasma persists for months to years and thus may falsely indicate a recent infection. Serological screening for T. gondii infection is not currently included in routine antenatal testing in New Zealand. The aim of this study was to determine the prevalence of IgG and IgM antibody to T. gondii in pregnant Auckland women.
Methods: Five hundred serum samples submitted for routine antenatal blood tests were tested anonymously for IgG and IgM antibodies to T. gondii. One hundred consecutive serum samples were tested from five age groups: <20, 21-25, 26-30, 31-35, >36 years. The number of positive IgM results that would have occurred if there were routine screening for toxoplasmosis was estimated for the year 2000 by multiplying the number of women giving birth in the respective age groups by the proportion with positive IgM results in these samples.
Results: One hundred and sixty three (33%) women had IgG antibody to T. gondii and 12 (2.4%) also had IgM antibody. For the year 2000, if there had been routine screening for toxoplasmosis, 296 of 14 530 (2.03%, 95% CI: 1.8-2.2%) pregnant Auckland women would have had a positive IgM result.
Conclusions: Screening would detect IgM antibodies in up to 2.2% of pregnant women. Significant and invasive further investigations would be required to identify the subset of pregnancies with fetal infection. Serological tests that are specific for recent primary infection are needed before routine screening could be considered for New Zealand. In the meantime, advice on how to avoid infection is necessary given that two thirds of pregnant Auckland women are susceptible to T. gondii.