Detection of Group B Streptococcus during antenatal screening in Western Australia: A comparison of culture and molecular methods.

AIM: Global screening strategies for Group B Streptococcus (GBS) include risk- or culture-based methods to guide intrapartum prophylaxis. In Western Australia (WA), antenatal culture-based screening is routine, however, numerous culture methods exist, in addition to molecular methods. We aimed to assess the comparability of research and diagnostic screening approaches.

METHODS AND RESULTS: Vaginal and rectal swabs were self-collected by pregnant women (n=531) from King Edward Memorial Hospital, WA, in parallel to routine screening (35-37 weeks gestation). Research methods involved culture (Strep B Carrot Broth™ and StrepB CHROMagar™ ) and molecular methods (real-time PCR), and were compared to routine diagnostic screening (Lim Broth and Granada agar). Overall, GBS detection was comparable between research and diagnostic approaches (3-5% discrepancy, kappa=0·76). Specificity/sensitivity of Carrot Broth™ was 100%/~89%, while CHROMagar™ was 73%/100%, respectively. Direct PCR was unable to detect GBS in ~18% of specimens which were culture positive, however, it exhibited 100% specificity.

CONCLUSIONS: This clinical evaluation of GBS screening methods provides support for current practice.

SIGNIFICANCE AND IMPACT: Although CHROM was highly sensitive, further testing is recommended due to a high false positive rate. Molecular assays are useful for rapid detection, however, low titre samples may require additional enrichment prior to molecular analysis to improve sensitivity. This article is protected by copyright. All rights reserved.