Usefulness of serological assays in diagnosis of early phase of toxoplasma gondii infection

OBJECTIVE: The aim of the study was to evaluate value of certain serological assays in differential diagnosis between early and late phase of T. gondii infection. METHODS: 92 patients (58 with nodular toxoplasmosis and 34 asymptomatic women with T. gondii infection diagnosed during or after pregnancy) with different time from onset of infection were tested for T. gondii antibodies with IFA, ISAGA IgM, ELISA IgM, ELISA IgA and IgG avidity assays. Sensitivity and specificity of certain assays was evaluated. RESULTS: IFA had sensitivity 76.19% with specificity 31.67%, ISAGA IgM and ELISA IgM had sensitivity 100% with specificity 16.67% and 23.33% respectively. ELISA IgA had sensitivity 76.19% or 85.71% depending on counting borderline results to positive or negative, with specificity 35% and 25% respectively. IgG avidity had sensitivity 100% with specificity 41.67%. CONCLUSIONS: All evaluated assays have only limited value in differentiation between early and late toxoplasmosis. IgA assay is not superior to IgG and IgM assays. IgG avidity is the most specific and sensitive method of such differentiation.