Evaluation of an in-house real-time polymerase chain reaction method to identify group B streptococcus colonization in pregnancy

Aim: The aim of this study was to evaluate the performance of in-house real-time polymerase chain reaction (qPCR) in detecting group B streptococcus (GBS) colonization compared with the standard culture method in a cohort of pregnant women. Material and Methods: total of 134 rectovaginal swabs were collected from 125 pregnant women, of whom 108 were known carriers or presented with preterm prelabor rupture of membranes. The swabs were placed in Standard Methods Broth (Todd-Hewitt broth supplemented with 6 mu g/mL gentamicin and 15 mu g/mL nalidixic acid) for culture identification of GBS. An in-house qPCR was also performed from the broth and after overnight incubation of the broth. Results: The detection rate of GBS in this cohort was 30.6% and 50.7% using standard culture method and qPCR, respectively. GBS-specific qPCR assay gave sensitivities of 97.6% and 100%, specificities of 73.1% and 71.0%, and negative predictive values of 98.6% and 100% from direct specimen and from broth after overnight incubation, respectively. Conclusions: The in-house qPCR test has high sensitivity in detecting GBS colonization. The high negative predictive value helps to avoid unnecessary use of antibiotics in uncolonized women.