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

Abstract

CULTURE IN DETERMINING GROUP B STREPTOCOCCUS COLONIZATION MICHAEL GAVINO, EILEEN WANG, University of Chicago, Obstetrics and Gynecology, Chicago, Illinois OBJECTIVE: To evaluate a new rapid, real-time polymerase-chain reaction (PCR)-based assay in the intrapartum detection of Group B Streptococcus (GBS) colonization STUDY DESIGN: This is a prospective observational study where term patients were consented at the University of Chicago clinics after GBS screening at 35-37 weeks gestation. During admission for delivery, paired rectovaginal swabs were obtained–one swab for the rapid GBS assay employing the real-time PCR GeneXpert System (Cepheid, Sunnyvale, CA) with easy sample preparation, GBS target amplification and detection in a single cartridge in under 90min, the other for standard culture. The GBS carriage rate was calculated for the study population. Using the intrapartum culture as the gold standard, the sensitivities, specificities, and predictive values of the rapid GBS test and the 35-37 week culture were determined. Fisher’s exact chisquare test was used to assess for statistical significance. RESULTS: Fifty-five subjects had data from both the rapid test and intrapartum culture. The GBS colonization rate by intrapartum culture was approximately 43.6%. Compared with intrapartum culture, the rapid molecular test had a sensitivity of 95.8%, specificity of 64.5%, positive predictive value of 67.6%, and negative predictive value of 95.2% (p-values !0.0001). In addition, the real-time PCR test was more sensitive than the antenatal culture which had a sensitivity of 83.3%, a specificity of 80.6%, a positive predictive value of 76.9% and negative predictive value of 86.2%. CONCLUSION: This pilot study suggests that the GeneXpert rapid GBS test is highly sensitive for the intrapartum detection of GBS. The GBS colonization rate in this group of predominantly African American Medicaid patients was higher than generally reported. This study supports the feasibility of using this assay when the GBS status is unknown i.e. with patients without prenatal care, to allow for more selective use of antibiotic prophylaxis. A costbenefit analysis is underway to better delineate the potential implementation of this new technology.