Evaluation of polymerase chain reaction on amniotic fluid for diagnosis of congenital toxoplasmosis

Abstract

The present study assessed sensitivity and specificity of PCR targeting P30 gene in diagnosis of congenital toxoplasmosis using amniotic fluid samples. A total of 358 pregnant women in their first trimester of pregnancy, most of them were asymptomatic while the others suffered lymphadenopathy, fever and/or malaise. The serum sample from each woman was screened for Toxoplasma-specific ELISA IgM & IgG. Sero-negative females were then screened in 2nd & 3rd trimesters for sero-conversion. Amniocentesis was performed to seropositive and sero-converted women. Detection of Toxoplasma DNA in AF was done by animal inoculation and PCR targeting P30 gene. 85/358 women were sero-positive for Toxoplasma. Congenital infection was detected in 14/85 fetuses by MI. One mouse had tachyzoite in peritoneal exudate while other 13 showed cysts in histpathological sections of mice. PCR test targeting P30 gene was positive in 13 with additional four fetuses, only PCR gave positive results, and serologic follow-up of suspected fetuses (17) by IgM ELISA confirmed congenital toxoplasmosis. Sixteen cases of congenitally infected newborn were a symptomatic. One was clinically diagnosed (ventricular dilatation) by the ultrasound. The PCR drastically changed the diagnostic repertoire for prenatal diagnosis. The sensitivity and specificity of PCR targeting P30 gene on AF samples were 92.9% & 94.4% respectively while positive predictive value (PPV) was 76.5%, and negative predictive value (NPV) was 98.5%. Its disadvantages were in fact that negative result cannot exclude acute infection, and thus must be confirmed by MI and it is also an expensive technique.