The ability to discriminate between primary
Toxoplasma gondii infection acquired in early pregnancy and
infection that occurred prior to pregnancy was assessed by an
enzyme immunoassay (EIA) to determine the avidity of toxoplasma-specific
immunoglobulin G (
IgG). The results were compared to those of the Platelia Toxo-
IgM EIA and the
dye test. The mean
IgG avidity of 73 serum samples collected within 20 weeks after the estimated time of
infection was 5.9%. Among 26 serum samples showing
latent infection (toxoplasma-specific
IgG positive and
IgM negative) and 56
IgM-positive serum samples with a low
dye test titer (<300 IU/ml), the mean avidities were 51.3 and 57.5%, respectively. A total of 72.8% of 92
IgM-positive serum samples with a high
dye test titer (>300 IU/ml), suggesting a recent toxoplasma
infection, had an
IgG avidity of >20%, indicating that the
infection started more than 20 weeks earlier. By introducing high
IgG avidity as a criterion in the first half of pregnancy to exclude the possibility that toxoplasma
infection was acquired during gestation, many women will avoid unnecessary examinations, treatment, and anxiety.