Real-Time PCR detection of group B streptococci from pregnant women's vaginal specimens at time of delivery: clinical evaluation

Guidelines for prevention recommend intrapartum antimicrobial prohylaxis (IAP) for pregnant women with a positive prenatal culture-based screening for GBS. To improve this strategy, a rapid screening performed at the onset of labor with the IDI-Strep BTM test (IDI), a real time PCR detection (Infectio Diagnostic), may be used.
Objective: To evaluate the performance of the IDI to detect GBS from vaginal specimens collected at time of delivery.
Methods: Intrapartum vaginal specimens from 923 pregnant women were tested to determine the status of GBS colonization, by CDC’s recommended culture method (including selective LIM broth) with a Granada agar (GR) added as well as by the IDI and the immunologic StrepB OIATM test (OIA), BioStar. The performance of the different methods was compared.
Results: GBS were recovered from 16.8% and 23.6% specimens respectively on primary culture plates and overall. The colonization rate for GBS was 18.6 % by IDI and 15.7 % by OIA testing. The sensitivity of IDI for identifying vaginal colonization status at delivery was 92 % or 77.1 % when compared to GR primary cultures or to overall culture results, and for the OIA, it was respectively 65.1 or 52.1 %. The specificity was 99.1 % for IDI and 95.5 % for OIA. The turnaround time for obtaining results was less than one hour for
both IDI and OIA.
Conclusions: 1) Strep B-IDI test, performed on intrapartum vaginal specimens, yields relevant results rapidly enough to be used as an efficient diagnostic tool for the identification of GBS colonized women, in order to offer IAP really targeted to GBS carriers. 2) By comparison to the prenatal screening-based strategy, the high sensitivity and specificity of IDI would allow a reduction of useless IAP and of missed opportunities. 3) IDI testing might be implemented “in routine” in some hospitals for further clinical and practical evaluation.