Determination of anti-Toxoplasma gondii immunoglobulin G avidity: adaptation to the Vidas system (bioMérieux).

The determination of specific anti-Toxoplasma gondii IgG avidity has been proposed to improve the determination of the date of toxoplasmic seroconversion in pregnant women. In this study, we adapted this serological technique to the Vidas system (bioMérieux) using 6 M urea as the dissociating agent. We studied 356 sera, including 42 sequential sera from sero-conversions in pregnant women. Our results show that the test is easy to use, and that an avidity index higher than 0.300 allows the exclusion of a recent infection acquired less than 4 months before serum sampling.