title: Novel interpretation of molecular diagnosis of congenital toxoplasmosis according to gestational age at the time of maternal infection.
abstract: 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.
authors.affiliation: Centre Hospitalier Régional Universitaire (CHRU) of Montpellier and University Montpellier I (Faculty of Medicine), Department of Parasitology-Mycology and Molecular Biology Pole of the French National Reference Centre for Toxoplasmosis, Montpellier, France.
authors.forename: Yvon
authors.initials: Y
authors.lastname: Sterkers
authors.forename: Francine
authors.initials: F
authors.lastname: Pratlong
authors.forename: Sahar
authors.initials: S
authors.lastname: Albaba
authors.forename: Julie
authors.initials: J
authors.lastname: Loubersac
authors.forename: Marie-Christine
authors.initials: MC
authors.lastname: Picot
authors.forename: Vanessa
authors.initials: V
authors.lastname: Pretet
authors.forename: Eric
authors.initials: E
authors.lastname: Issert
authors.forename: Pierre
authors.initials: P
authors.lastname: Boulot
authors.forename: Patrick
authors.initials: P
authors.lastname: Bastien
mesh_terms: D000293:Adolescent; D000328:Adult; D000653:Amniotic Fluid / Q000469:parasitology; D005260:Female; D005312:Fetal Blood / Q000469:parasitology; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D025202:Molecular Diagnostic Techniques / Q000379:methods*; D010920:Placenta / Q000469:parasitology; D016133:Polymerase Chain Reaction; D011247:Pregnancy; D011251:Pregnancy Complications, Infectious / Q000175:diagnosis*; D012680:Sensitivity and Specificity; D013997:Time Factors; D014125:Toxoplasmosis, Congenital / Q000175:diagnosis*; D014481:United States; D055815:Young Adult