Diagnosis of congenital Toxoplasma gondii infection by polymerase chain reaction (PCR) on amniotic fluid samples - The Norwegian experience

As part of a screening project for detection of Toxoplasma gondii infection among pregnant women in Norway, nested polymerase chain reaction (PCR) aimed at the detection of T. gondii in amniotic fluid samples was included in the diagnostic routine. The results were compared with the routine criteria for congenital infection: i) T. gondii detected in amniotic fluid or cord blood by mouse inoculation, ii) specific IgM or IgA in serum collected after birth, and/or iii) specific IgG persisting beyond one year of age. The PC-R was based on the BI gene with an internal control gene amplified together with the BI gene. One hundred and two amniotic fluid samples collected during pregnancy and/or at delivery from 67 pregnant women with serological evidence of primary T. gondii infection were available for examination by both BI-PCR and mouse inoculation. Six samples were positive and 86 samples were negative by both methods (90% concordance). One sample was mouse inoculation positive and BI-PCR negative while nine samples were BI-PCR positive and mouse inoculation negative, of which five were associated with four infants without proven infection. 59% and 41% of samples associated with infected infants were positive by BI-PCR and mouse inoculation, respectively. The difference was mainly due to a lower detection rate by mouse inoculation after antiparasitic treatment. The specificity of BI-PCR was 94%. Even though BI-PCR performed on amniotic fluid samples did not detect all infected infants, it represented a valuable tool in addition to conventional methods in the diagnosis of congenital T. gondii infection.