Congenital Toxoplasmosis Diagnosed Early By Molecular Test

A molecular test has been validated as a method to affirm the diagnosis of congenital toxoplasmosis (CT) using neonatal peripheral blood.

A polymerase chain reaction (PCR) assay was found to be a sensitive, rapid, and cost-effective method to affirm the diagnosis of previously undiagnosed congenital toxoplasmosis using blood from very young infants.

Scientists at the University of Montpellier I (France) prospectively enrolled all successive neonates who had blood sampled for molecular diagnosis of CT before the age of three weeks from March 2003 to December 2008, in the Languedoc-Roussillon region, in southern France. A series of tests were performed on amniotic fluid, placenta, and cord blood by a highly performing conventional PCR that has shown excellent sensitivity as compared with other real-time PCR assays and mice inoculation. Serologic follow-up during the first year of life for immunoglobulin (Ig) IgG, IgM, and IgA by enzyme linked immunosorbent assay (ELISA), immunofluorescence, and/or immunosorbent agglutination assay (ISAGA), and comparative immune charge relating specific IgG to total IgG.

In a cohort of 12 consecutive neonates, the PCR assay established the diagnosis of five of six cases of congenital toxoplasmosis and did so earlier than serologic methods. In all cases of CT, the maternal infection occurred in the third trimester. The PCR tests were performed using neonatal peripheral blood on day-two to day-four for eight cases, one case on day 10 and three cases on day 15. The PCR was positive in 83% of the cases of CT and negative in the remaining cases. In one neonate, the positive PCR using peripheral blood was the first test, which affirmed the diagnosis of CT. In the cohort, one false-negative molecular test was recorded, emphasizing that the diagnosis of CT is difficult and often needs a combination of laboratory tests.

The authors concluded that with a low false-negative rate and no false-positive result, PCR on neonatal peripheral blood was validated as it can be performed routinely. The assay is able to affirm the diagnosis of CT and perhaps render the first positive result. The study was published on August 8, 2011, in the journal Diagnostic Microbiology and Infectious Disease.

Related Links:
University of Montpellier I