Diagnosis of Congenital Toxoplasmosis: Performance of Four IgG and IgM Automated Assays at Birth in a Tricentric Evaluation.

For postnatal diagnosis of congenital toxoplasmosis (CT), the gold standard for the detection of anti-Toxoplasma IgM in newborns relies on the immunosorbent agglutination assay (ISAGA), which is manufactured from whole Toxoplasma parasites that become difficult to maintain. For IgG, only the Platelia assay provides a validated assay for cord blood according to the manufacturer, allowing its use in this context. We compared the analytical performance of four commercialized automated assays, Platelia, Abbott, Vidas, and Liaison, for the detection of IgG and IgM in the cord blood or peripheral blood of newborns from women infected during pregnancy. The assays were performed on samples from 509 newborns, collected from the university hospitals of Montpellier, Nîmes, and Toulouse. For IgM, the four assays appeared to be sufficiently informative to be used for congenital toxoplasmosis diagnosis (area under the curve [AUC] > 0.8, receiver operating characteristic [ROC] analysis), with Platelia showing the best performance, similar to ISAGA with regard to accuracy (83%). For the Vidas (76%), Abbott (75%), and Liaison (74%) assays, the accuracy was significantly lower. Maternal treatment significantly decreased the sensitivity of all the assays. For IgG, the four evaluated assays showed a sensitivity of over 90%, with Abbott (95%) and Liaison (94%), exhibiting a significantly higher sensitivity than Platelia (90%). Furthermore, Abbott showed its superiority in the cases of maternal infection during the third trimester. In the context of the newborns of mothers infected by Toxoplasma gondii during pregnancy, to ensure efficient care, Platelia and Abbott seemed to be the most suitable reference tests for the detection of IgM for the former and IgG for the latter.

Diagnosis of Congenital Toxoplasmosis: No Benefit of IgA Antibody Detection by Platelia ELISA in a Tricentric Evaluation.

The diagnostic accuracy of a commercial Toxoplasma gondii IgA antibody enzyme-linked immunosorbent assay (ELISA) was evaluated in the context of routine practice on 289 newborns with congenital toxoplasmosis (CT) and 220 healthy controls. The performance of this assay was compared to that of the current gold-standard test for anti-Toxoplasma IgM detection, an immunosorbent agglutination assay (ISAGA). IgM and IgA sensitivity and specificity were assessed in cord and postnatal samples. The sensitivity of IgA detection by ELISA on all serum and peripheral blood samples was 60.56% and 56.52%, respectively, which is low compared with the sensitivity of IgM detection by ISAGA (73.26% on serum samples, 82.35% on peripheral blood). Adding the T. gondii IgA antibody ELISA to the diagnostic panel did not significantly increase the overall performance of the serological diagnosis based on IgM detection.

Molecular diagnosis of toxoplasmosis at the onset of symptomatic primary infection: A straightforward alternative to serological examinations.

Myopericarditis is a rare but well-documented clinical presentation of primary Toxoplasma gondii infection in immunocompetent patients. Here, early detection of Toxoplasma DNA in the peripheral blood by PCR allowed the diagnosis of acute toxoplasmosis while serological tests were negative. Additional serological evaluations 2 weeks later confirmed the diagnosis and showed that cardiac manifestations occurred before seroconversion. This highlights the importance of a second serological control in the case of a suspected active infection. Overall, we show here that PCR testing for Toxoplasma is a sensitive and straightforward alternative to serological examinations.

Novel interpretation of molecular diagnosis of congenital toxoplasmosis according to gestational age at the time of maternal infection.

From a prospective cohort of 344 women who seroconverted for toxoplasmosis during pregnancy, 344 amniotic fluid, 264 placenta, and 216 cord blood samples were tested for diagnosis of congenital toxoplasmosis using the same PCR assay. The sensitivity and negative predictive value of the PCR assay using amniotic fluid were 86.3% and 97.2%, respectively, and both specificity and positive predictive value were 100%. Using placenta and cord blood, sensitivities were 79.5% and 21.2%, and specificities were 92% and 100%, respectively. In addition, the calculation of pretest and posttest probabilities and the use of logistic regression allowed us to obtain curves that give a dynamic interpretation of the risk of congenital toxoplasmosis according to gestational age at maternal infection, as represented by the three sample types (amniotic fluid, placenta, and cord blood). Two examples are cited here: for a maternal infection at 25 weeks of amenorrhea, a negative result of prenatal diagnosis allowed estimation of the probability of congenital toxoplasmosis at 5% instead of an a priori (pretest) risk estimate of 33%. For an infection at 10 weeks of amenorrhea associated with a pretest congenital toxoplasmosis risk of 7%, a positive PCR result using placenta at birth yields a risk increase to 43%, while a negative result damps down the risk to 0.02%. Thus, with a molecular diagnosis performing at a high level, and in spite of the persistence of false negatives, posttest risk curves using both negative and positive results prove highly informative, allowing a better assessment of the actual risk of congenital toxoplasmosis and finally an improved decision guide to treatment.

Diagnosis of congenital toxoplasmosis by polymerase chain reaction on neonatal peripheral blood.

In a cohort of 12 consecutive neonates, polymerase chain reaction (PCR) established the diagnosis of 5 of 6 cases of congenital toxoplasmosis and did so earlier than serologic methods. We validated that PCR using neonatal peripheral blood is a sensitive, rapid, and cost-effective method to affirm the diagnosis of previously undiagnosed congenital toxoplasmosis.

Value of 2 IgG avidity commercial tests used alone or in association to date toxoplasmosis contamination.

Toxoplasmosis acquired during pregnancy exposes the fetus to congenital toxoplasmosis. Avidity tests are commonly used to date time of infection to evaluate the fetal risk and to offer prenatal diagnosis. This study evaluated and compared 2 commercial avidity tests: Platelia Toxo IgG Avidity (Bio-Rad, Marnes la Coquette, France) and Liaison(R) Toxo IgG Avidity II (Diasorin, Saluggia, Italy) kits. In complement, a study of specific IgG and IgM in the 2 systems was carried out. Sensitivity and specificity of the avidity tests were 94.4% and 87.8% for the Liaison(R) and 91.3% and 98.5% for the Platelia methods, respectively. Percentages of complete discrepancies, partial discrepancies, and agreement between both tests were 1.1%, 23.6%, and 75.3%, respectively. Moreover, the combination of both avidity tests may be useful in some cases. Indeed, that strategy permitted to confirm without delay a chronic toxoplasmosis in 23 cases and avoid treatment in these pregnant women.