A comparison of a new rapid real-time polymerase chain reaction system to traditional culture in determining group B streptococcus colonization

OBJECTIVE: The objective of the study was to evaluate a rapid real-time polymerase chain reaction ( PCR) - based assay for intrapartum detection of group B streptococcus ( GBS). STUDY DESIGN: This prospective, observational study enrolled outpatients after GBS screening at 35- 37 weeks' gestation. At admission for delivery, paired rectovaginal swabs were obtained for the GBS GeneXpert ( Cepheid, Sunnyvale, CA) assay and standard culture. Using the intrapartum culture as the gold standard, sensitivities, specificities, and predictive values of the rapid assay and the antenatal screen were determined. Statistical significance was determined by Fisher's exact test. RESULTS: Fifty- five subjects had both rapid test and intrapartum culture results. The intrapartum GBS colonization rate was 43.6%. The sensitivity and specificity of the PCR test were 95.8% ( 95% confidence interval [ Cl], 76.9- 99.8%), and 64.5% ( 95% Cl, 45.4- 80.2%), respectively, whereas the antenatal culture sensitivity was 83.3% and specificity was 80.6%. CONCLUSION: The GeneXpert rapid GBS point- of- care assay was highly sensitive for GBS detection in our sample population. Corroboration of these data is needed on a large population basis.