Direct Identification of Streptococcus agalactiae in Vaginal Colonization in Pregnant Women Using Polymerase Chain Reaction

Streptococcus agalactiae is a commensal organism, but it may cause infection in susceptible hosts including newborns as well as in pregnant or postpartum women. Applying rapid, accurate and sensitive methods for detecting group B Streptococcus (GBS) and receiving intrapartum antibiotic prophylaxis (IAP) at delivery have been demonstrated to increase the treatment possibility of carrier pregnant women and decrease the rates of GBS vertical transmission to infants. The aim of this study was to compare the PCR assay results targeting 16S rRNA primers with the conventional culture method for direct detection of GBS in vaginal specimens of pregnant women at 35-37 weeks of gestation in Hamadan, Iran. A total of 203 vaginal specimens of pregnant women at 35-37 weeks of pregnancy from June 2013 through February 2014 were evaluated for detection of GBS, using culture method and polymerase chain reaction (PCR). The prevalence of GBS in the 203 collected samples was 7.39% using culture method and 19.70% using PCR. Twenty-five specimens had positive PCR results and negative cultures; two specimens were positive in culture and negative by PCR.A total of 42 specimens (20.69%) were considered as true positive. The PCR results in comparison with culture (as the gold standard) revealed sensitivity of 88.24%, specificity of 87.44%, positive and negative predictive value of 35.71% and 98.95% respectively, and accuracy of 87.50%. Performing only culture method led to missed false negative carriers. Therefore, it is recommended that both the PCR assay and conventional culture method be routinely performed to detect GBS in pregnant women accurately. PCR diagnosis demonstrated a shorter turnaround time when compared with the time consuming culture method.