Comparison of the efficiency of two commercial kits - ELFA and Western blot in estimating the phase of Toxoplasma gondii infection in pregnant women.

Sera of 89 pregnant women were selected according to the results of ELFA IgM, IgG and avidity IgG, and tested with commercial tests IgM, IgG and avidity IgG Western Blot (WB) to compare the efficacy of both techniques in determining the phase of T. gondii infection. In total, 81 of 89 tested sera (91.0%) were classified as positive, both in the ELFA and WB tests for the presence of anti-Toxoplasma antibodies of class IgG, indicating a past infection, while the prevalence of anti-Toxoplasma positive reactions associated with the antibodies of class IgM indicating a recent infection was much lower - 31.5% and 20.2%, respectively. Sera of 81 women were also tested in the ELFA and WB tests for avidity, e.g. ability of forming high-molecular IgG antibody complexes. Low or medium results in these tests (in this study all classified as low), indicating a recent infection, were detected by ELFA and WB in 22.2% and 45.7% of the total examined samples, respectively. The Spearman's rank test for correlation, performed for recognition of quantitative data of the ELFA and WB tests (index, units or points), revealed a highly significant correlation between the ELFA and WB tests for homologous classes of antibodies, both for IgM and IgG (p<0.00001). In contrast, the ELFA and WB tests for detection of anti-Toxoplasma IgM antibodies were not correlated with the ELFA and WB tests for detection of anti-Toxoplasma IgG antibodies (p>0.05), except for the WB test for IgM antibodies, which showed a significant correlation with the ELFA test for IgG antibodies (p<0.01). A highly significant negative correlation between the ELFA and WB test for IgM antibodies and ELFA and WB tests for IgG avidity was demonstrated (p<0.01), except for a relationship between the WB test for IgM and WB for avidity, which was not significant. Such negative correlations are theoretically expected, as strong complexes with the participation of IgG antibodies are absent in the early phase of toxoplasmosis when early antibodies of IgM class are present. Summarizing, this study indicates the high usefulness of the commercial ELFA and WB tests in serodiagnostics of toxoplasmosis in pregnant women. Special attention should be paid to parallel detection of IgM antibodies and low values in the ELFA and WB tests for IgG avidity, which indicates a recent infection which may be associated with a clinical form of congenital toxoplasmosis and damage to the foetus.