Detection of Acute Toxoplasma gondii infection in early pregnancy by IgG-avidity and PCR analysis

Objective: To detect acute Toxoplasma gondii (T. gondii) infection in early pregnancy Introduction: Acute Toxoplasma gondii (T. gondii) infection in early pregnancy carries the risk of transmitting the infection to the fetus with serious sequelae. However, serological testing for IgG/IgM anti-Toxoplasma antibodies may fail to differentiate between a recent and past infection. Methods: 224 Kuwaiti women in their first trimester were screened for IgG/IgM antibodies by Vitek Immuno Diagnostic Assay System (VIDAS) and VIDAS IgG-avidity tests. Results & Discussion: On serological screening, 119 (53.1%) women were IgG-positive antibodies and 31 (13.8%) for IgM antibodies. Nine of the IgM-positive and 7 IgM-negative women had low avidity antibodies. However, IgG avidity test detected low avidity antibodies only in 9 (29%) of the 31 IgM-positive women suggesting a recent infection; and 19 (61.3%) women had high avidity antibodies indicating the infection was acquired in the distant past. Based on IgM serology alone, at least 31 IgM-positive women may have been wrongly labeled with acute Toxoplasma infection thus warranting appropriate therapeutic intervention. All the 19 IgM-positive women with high avidity were confirmed negative for Toxoplasma DNA on PCR analysis. Compared with PCR analysis the VIDAS avidity test was a helpful tool for the diagnosis of recent Toxoplasma infection in IgM-negative women with low-avidity and IgM-positive women with high avidity, specificity >85% to 100% respectively. Conclusion: The VIDAS avidity test when used in combination with VIDAS IgG/IgM tests is a valuable assay for the exclusion of ongoing or recently acquired T. gondii infection in pregnant women in their first trimester and that it decrease significantly the necessity for follow-up testing and unnecessary therapeutic intervention.