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In Utero and at Birth Diagnosis of Congenital Toxoplasmosis: Use of Likelihood Ratios for Clinical Management

Rabilloud, Muriel MD, PhD*†‡§¶; Wallon, Martine MD, PhD∥**††; Peyron, François MD, PhD∥**††

The Pediatric Infectious Disease Journal: May 2010 - Volume 29 - Issue 5 - p 421-425
doi: 10.1097/INF.0b013e3181c80493
Original Studies

Background: The results of the ante- and neonatal diagnostic tests for congenital toxoplasmosis influence the decision to treat the newborn immediately after birth. Here, we estimate the positive and negative likelihood ratios (LRs) and the probabilities of congenital infection according to PCR and IgM-IgA tests results.

Methods: The study concerned 767 children born between 1996 and 2002 and followed-up for 1-year at Croix-Rousse hospital, Lyon, France. The LRs and the post-test probabilities were estimated conditionally on gestational age at maternal infection using a logistic regression approach.

Results: For the PCR and the IgM-IgA tests, the positive LRs were high. In children with one positive test when only one test was done, the probability of infection reached 90% when the maternal infection occurred at 18-weeks gestation or later. This probability was close to 100% when the 2 tests were positive, whatever the gestational age. The negative LRs of the 2 tests moved closer to 0 at later gestational ages. However, when the tests were negative, the probability of infection remained greater or equal to 10%, except in early maternal infection. When the 2 tests were discordant, the probability of infection was about 50% in early maternal infection.

Conclusion: Providing reliable probabilities of congenital infection, the PCR and IgM-IgA tests guide clinical management and counseling of parents.


From the *Hospices Civils de Lyon, Service de Biostatistique, Lyon, France; †Université de Lyon, Lyon, France; ‡Université Lyon I, Villeurbanne, France; §CNRS; ¶UMR 5558, Laboratoire de Biométrie et Biologie Evolutive, Equipe Biostatistique Santé, Pierre-Bénite, France; ∥Hospices Civils de Lyon, Service de parasitologie, Hôpital de la Croix Rousse, Lyon, France; **Université de Lyon; and ††Université Lyon 1, Service de parasitologie, Faculté de médecine Lyon Nord, Lyon, France.

Accepted for publication October 27, 2009.

Supported by the Hospices Civils de Lyon.

Address for correspondence: Muriel Rabilloud, MD, PhD, Hospices Civils de Lyon-Service de Biostatistique, 162 Avenue Lacassagne, 69424 Lyon Cedex 03, France. E-mail:

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© 2010 Lippincott Williams & Wilkins, Inc.