Prenatal diagnosis of rubella virus infection by direct detection and semiquantitation of viral RNA in clinical samples by reverse transcription-PCR

A reverse transcription-nested PCR (RT-nPCR) method for prenatal diagnosis of rubella virus (RV) infection was developed, In the first step of RT-nPCR a synthetic RNA molecule (pRRV) differing from the RV target sequence by having a 21-nucleotide insertion was used as the internal control of amplification for the detection of PCR inhibitors, In addition, comparison of pRRV and RV-specific PCR signals allowed for the semiquantitation of RV input target sequences (range, 10 to greater than or equal to 1,000 RV genomes). In parallel, a complete RT-nPCR assay was performed with the same samples in the absence of the internal control to confirm the results of the first step and to detect RV RNA-positive samples containing <10 RV genomes, Subsequently, the RT-nPCR method was used to examine retrospectively clinical samples (direct RT-nPCR) from eight congenitally infected and eight uninfected fetuses for RV RNA, RT-nPCR was also used to detect RV RNA in cell cultures (culture-RT-nPCR) 96 h after inoculation with the same specimens, With amniotic fluid (AF) samples, direct RT-nPCR identified eight of eight cases of RV transmission (sensitivity, 100%), whereas culture-RT-nPCR and virus isolation detected only six of eight cases (sensitivity, 75%), However, when the culture-RT-nPCR results were positive, culture-RT-nPCR confirmed the direct RT-nPCR results 3 days to 3 weeks earlier than virus isolation, The specificity of direct RT-nPCR was 100%, with eight of eight uninfected fetuses being negative. Semiquantitation showed only small amounts (less than or equal to 100 copies) of viral RNA in clinical samples. In conclusion, direct RT-nPCR with AF samples (i) shows 100% sensitivity and specificity for prenatal diagnosis of RV infection and (ii) is a rapid technique, giving results in 24 to 48 h after sampling.