Evaluation of IgG Avidity for Diagnosis of Acute Toxoplasma gondii Compared to Nested PCR in Pregnant Women in First Trimester

Toxoplasma gondii (T. gondii) is intracellular protozoa. Infection with T. gondii can result in a serious sequel to the fetus if infection occurs in the first trimester of pregnancy. Laboratory diagnosis is the main method of diagnosis.

The aim of the present study was to detect recent infection with Toxoplasma gondii in cohort pregnant Egyptian women in the first trimester by serological detection of concrete IgM, IgG and IgG avidity test. The results of serological tests were compared by nested PCR method.

One hundred and twenty pregnant women in the first trimester of pregnancy were included in the study. Blood samples were obtained and subjected to serological studies for specific immunoglobulins M (IgM), G (IgG) and avidity IgG for T. gondii. Suspected results were confirmed by nested polymerase chain reaction for detection of T. gondii DNA.

Positive IgG for Toxoplasma gondii was (31.7%) and positive IgM was (18.3%). IgG avidity results showed that low avidity IgG and high avidity IgG represented 31.7% for each of positive IgG for Toxoplasma while intermediate avidity represented 36.8%, Table 1.

Twenty two pregnant women were positive for IgM, however, only 7 of them (31.2%) were associated with low avidity IgG suggesting recent infection. Seven positive IgM results were associated with high IgG avidity (31.2%) and 8 positive IgM samples were associated with boarder line IgG avidity results (36.4%). Among pregnant women with negative IgM, isolated, low avidity IgG was found in five patients (5.1%), boarder line IgG avidity in 6 patients (6.1%) and high IgG avidity in 5 patients (5.1%). We studied 26 pregnant women with nested PCR to confirm serological test results to detect recent Toxplasma infection. Among women with positive IgM with boarder line avidity IgG only 2 were positive by PCR while 8 (80%) were negative. On the other hand three women with isolated low avidity IgG were positive by PCR (60%) and 2 were negative. All women with positive IgM and high avidity IgG were negative by PCR and all women with isolated boarder line IgG avidity were negative also by PCR. According to this table, the sensitivity of IgG avidity test was 100 95%CI: 30.48–100, specificity 77.8% (95%CI: 40.06% - 96.53%) with a positive predictive value 60% (95% CI: 15.40% - 93.51%), and negative predictive value 100% (95% CI: 58.93% - 100.00%).

We can conclude that confirmatory testing for recent Toxoplasma infection with the combined use of IgG avidity with IgM antibody test in pregnant women during the first trimester has the potential to decrease the need molecular method for diagnosis and even the need for follow up samples for detection of diagnostic rising titer with delay of acute Toxoplasma diagnosis. The rapid and accurate diagnosis leads to appropriate therapeutic intervention in adequate time.