Difficulty in dating primary infections by Toxoplasma Gondii in pregnant women in Tunisia

In Tunisia, serological diagnosis of toxoplasmosis in pregnant women is generally ordered on the first prenatal consultation. As primary tools, IgG and IgM tests are done. Subsequent serological testing is performed to date infection in case of IgM positivity. IgG avidity measurement was done in 156 sera with IgM. The kit [Toxo Avidite] from SFRI was used. This commercial assay permits to rule out an infection acquired in the last 12 months in case of avidity index [AI]>0.6 and to suspect a recent infection acquired in the last 3 months in case of AI<0.3. 57.1% of pregnant women had an AI>0.6; 17.9% an AI<0.3 and 25% an intermediate AI. The high and middle IgG titles were frequently associated with an AI>0.6 whereas low titles were generally associated with an AI<0.6 [p<0.01] and particularly an IA<0.3. If an AI>0.6 is an indicator against primary infection during pregnancy and an AI<0.3 permits to order amniotic sampling for PCR, intermediate avidity dols not permit to conclude mainly because a great proportion of pregnant women do not lave their first prenatal consultation befoe the second trimester of pregnancy. In these cases search for IgA and follow up samples can be useful. To facilitate serological interpretation, the antibody status of pregnant women should be obtained in Tunisia, before or early in pregnancy.