An Evaluation of a Rapid Real Time Polymerase Chain Reaction Assay for Detection of Group B Streptococcus as Part of a Neonatal Group B Streptococcus Prevention Strategy

Objective: To evaluate the sensitivity, specificity, and feasibility of a rapid real-time polymerase chain reaction (PCR) test for group B streptococcus (GBS) completed during labour, compared with the standard culture test performed at 35 to 37 weeks' gestation. Methods: Women presenting to the maternity unit for term vaginal delivery had two vaginal/rectal samples collected. One swab was tested using a rapid PCR method (IDI-Strep B, lnfectio Diagnostic [IDI] Inc., Sainte-Foy QC), and the other was cultured after enrichment (intrapartum culture). Comparisons were made between these results and those of a culture-based screen at 35 to 37 weeks' gestation. Results: Of the 190 women enrolled, 85% had results of the standard screen at 35 to 37 weeks available for comparison. The sensitivity and specificity of the standard 35- to 37-week screen were 84.3% (95% confidence interval [CI], 71.4-93.0) and 93.2% (95% CI 86.5-97.2) respectively, whereas the sensitivity and specificity of the rapid PCR were 90.7% (95% CI 79.7-96.9) and 97.6% (95% CI 93.1-99.5), respectively. The median reporting time for the rapid PCR test was 99 minutes (range 50-255). Results were available more than four hours before delivery in 81% of cases. Conclusion: In this Canadian centre, a rapid PCR test done at the time of labour (IDI-Strep B) demonstrated high sensitivity and specificity, comparable to the 35- to 37-week screen. The time to reporting results was acceptably short, allowing for timely administration of intrapartum prophylactic antibiotics.