Intrapartum screening of group B Streptococcus using GeneXpert real-time PCR versus late antenatal screening by culture

Abstract number: P1981

El Helali N., Ly A., Nguyen J.C., Giovangrandi Y., Sauvanet E.

Objective: Actual prevention of neonatal early onset group B streptococcal (GBS) disease involves giving intrapartum antibiotics to women. It takes in account either their antenatal culture colonisation status or for those women with unknown status, the presence of risk factors. The aim of this study was to evaluate the accuracy of GeneXpert real-time PCR, for the detection of GBS carriers at the onset of labor, and to compare it to the current 35 to 37 weeks screening by culture.

Methods: Over a six-month period 630 women were prospectively enrolled. According to ANAES recommendations in France, specimens were collected at 35 to 35 weeks by swabbing the lower third of the vagina, and cultured by direct plating on sheep blood agar.

At time of presentation for delivery, the vaginal swab was repeated using a double Copan swab. Of these, one swab was processed by culture, and the other one by GenExpert real-time PCR which integrates the all processing (extraction-amplification-detection) in 70 minutes.

Results: Of enrolled women 89% were eligible for analysis. The GBS colonisation rate when using culture, was 16.1% intrapartum versus 13.16% at 35 to 37 weeks. Compared with intrapartum culture, the sensitivity of late antenatal culture for identifying colonisation status at delivery was 54.1% and the positive predictive value 66.25%. PCR results were not available for 11% of the samples: 5% due to PCR inhibition, 3% due to significant presence of mucus and 3% due to manipulation errors. Compared with intrapartum culture, the GeneXpert real-time PCR test had a sensitivity of 97.9%, a specificity of 99.7%, a positive predictive value of 98.9% and a negative predictive value of 99.6%. The molecular test was superior to antenatal culture: sensitivity 97.9% versus 54.1%.

Interestingly 9% of negative screened women at 35 to 37 weeks became positive on intrapartum, and 34% of positive screened women became negative. Of screened positive women on time of labor, 47% were not detected by antenatal culture.

Conclusion: The real-time PCR on GenExpert is a rapid test, highly sensitive and specific to detect GBS colonised women at time of labor. This molecular test is extremely easy to use as a laboratory routine test. The results could be available 24H a day for antibiotics prescription to be given before delivery.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
Back to top