T. Bodmer¹, A: Henle-Gross², K. Bögli-Stuber¹, S. Droz¹, D.V. Surbeck²

¹University of Berne, Institute for Infectious Diseases, Berne, Switzerland, ²University Hospital, Department of Obstetrics and Gynecology, Berne, Switzerland

Background: Early onset neonatal sepsis due to group B streptococci (GBS) causes severe morbidity and mortality in newborns. While different preventive strategies to identify women at risk are recommended, the optimal strategy depends on the incidence of GBS sepsis and on the prevalence of anogenital GBS colonization. The aim of this study was to evaluate the performance of the “GeneXpert real-time PCR” (GeneXpert GBS, Cepheid, Sunnyvale, CA) for the detection of GBS carriers at the onset of labour, and to compare it to the results obtained by culture.
Methods: Pregnant women who had given informed consent were prospectively enrolled in the study. At the onset of labour two swabs from the outer third of the vagina and the anal region were taken from each study participant. One swab was cultured (overnight enrichment in Todd-Hewitt broth, followed by subculturing onto blood agar plates incubated for 24 h at 35°C in 5% CO2) and the other was tested by the “GeneXpert real-time PCR” which integrates all the processing (extraction-amplification-detection) in 75 minutes. Sensitivity and specificity of GeneXpert GBS was assessed against culture as the reference, and time-to-result and ease-of-use were evaluated.
Results: To date, 135 women have been enrolled in the study. The anogenital GBS colonization rate was 18% (culture). Five patient specimens (4%) gave inconclusive PCR results (e.g. inhibition due to excess mucus) and were excluded from further analysis. The “GeneXpert real-time PCR” test had a sensitivity of 87%, a specificity of 97%, a positive predictive value of 87% and a negative predictive value of 97%. GeneXpert was easy to use, and the test results were available within 75 minutes.
Conclusions: The “GeneXpert GBS real-time PCR” test had a short turn-around-time and was easy to use. It proved to be sensitive and specific in detecting GBS carrying women at the onset of labour, and may thus have a role to play as a point-of-care test that can be performed at the onset of labour by the staff of maternity clinics. This question will be addressed during the second part of the study.