Both the Revogene GBS LB and GeneXpert GBS LB assays perform well for the detection of Group B Streptococcal (GBS) infections in pregnant women, according to a study published in BMC Infectious Diseases.

Roughly 25% of pregnant women demonstrate positive rectovaginal cultures for S agalactiae; while colonization with this bacteria is asymptomatic, it can cause severe infections including meningitis, sepsis and pneumonia in neonates born to colonized mothers. The neonatal mortality rate caused by GBS infection is high, therefore since 1996 the Centers for Disease Control and Prevention has recommended screening all pregnant women at 35 to 37 weeks of gestation and subsequent administration of intrapartum antibiotic prophylaxis as indicated. Despite these guidelines, infection with GBS remains a leading cause of morbidity in neonates born in the United States, thus highlighting the need for the implementation of more rapid and sensitive screening techniques for GBS detection to further reduce intrapartum transmission of GBS infection.

Therefore, researchers performed a clinical comparison of Xpert GBS LB and the novel, recently FDA-cleared test, Revogene GBS LB, for detecting GBS in pregnant women undergoing routine GBS screening. A total of 250 rectovaginal swabs were submitted to the University of Wisconsin’s clinical microbiology lab between December 2017 and February 2018. All enriched samples were first tested on the GeneXpert Dx system using the Xpert GBS LB assay. Following completion on the GeneXpert Dx system, the same LIM broth-enriched specimens were tested on the Revogene system.

The results of the 2 assays demonstrated that 96.8% were concordant (n=242) and 3.2% were discrepant (n=8). Among the 8 discrepant results, 7 specimens tested negative by GeneXpert but positive by Revogene, and 1 tested positive by GeneXpert, but negative by Revogene with initial testing. Repeat testing of the 7 discrepant samples that initially tested negative by GeneXpert found 3 that subsequently tested positive and 3 that tested negative. The positive percent agreement, negative percent agreement, and overall percent agreement between the Revogene and Xpert assays were 98.0% (95% CI, 89.6-99.7%), 96.5% (95% CI, 92.9-98.3%), and 96.8% (95% CI, 93.8-98.4%), respectively.

Investigators further evaluated time and cost of each assay. Results showed that the Xpert assay required roughly 1 minute less time to setup, and had an 11 minute shorter run time compared with Revogene. However, Reveogene had a list price of $28 per test, compared with $30 for Xpert; further, list price for instruments were $35,000 and $110,000, respectively.

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“There are specific differences listed in our study that laboratories should consider when deciding between the two,” the researchers suggested. “While the small consumable and equipment size of the Revogene are an advantage in terms of space requirements and waste management, the GeneXpert allows for the flexibility of adding on more modules, has a more extensive test menu, and specimens are tested individually.”

Reference

Choera T, Jung-Hynes B, Chen DJ. Comparative study of Revogene GBS LB assay and GeneXpert GBS LB assay for the detection of group B Streptococcus in prenatal screening samples. BMC Infect Dis. 2020;20(1):38