Advice

Summary

Summary

The Xpert GBS test detects group B streptococcus (GBS) colonisation in pregnant women, using rectal and vaginal swabs. One randomised controlled trial reported a sensitivity of 89% and a reduction in intrapartum antibiotic prophylaxis. Seven diagnostic accuracy studies reported that Xpert GBS has good sensitivity. The Xpert GBS test is run on the GeneXpert molecular diagnostic system and each test costs £38.80.

In current NHS practice, antibiotic prophylaxis is offered based on clinical risk factors without routine testing. If a rapid and effective test to detect GBS colonisation were adopted, it could reduce use of broad‑spectrum antibiotics in line with antibiotic stewardship guidelines.

Product summary and likely place in therapy

  • The Xpert GBS test is a rapid polymerase chain reaction (PCR) test for detecting group B streptococcus (GBS) colonisation in women who are about to give birth.

  • Guidelines from the Royal College of Obstetricians and Gynaecology and The National Screening Committee do not currently recommend routine screening for GBS at any stage during pregnancy. Additionally, NICE does not currently recommend selective testing for women considered to be at increased risk of GBS.

  • If a rapid and effective test to detect GBS colonisation were adopted, it could improve antibiotic stewardship. The Xpert GBS test could be used to identify GBS colonisation at the onset of labour as an adjunct to the risk factor based approach, and could potentially reduce the unnecessary use of intrapartum antibiotic prophylaxis.

Effectiveness and safety

  • One randomised controlled trial (n=229) included 2 phases: phase 1 reported a sensitivity of 89%, and a reduction in intrapartum antibiotic prophylaxis based on Xpert GBS results, but there was a high rate of invalid results (44%). Phase 2 used an upgraded version of the test and reported that the level of invalid results reduced to 15% (statistically significant reduction p<0.001).

  • One diagnostic accuracy and feasibility study (n=695) reported a sensitivity of 85%. Intrapartum antibiotic prophylaxis was possible for at least 4 hours in 73 of 107 women (68%) when based on the Xpert GBS test, compared with 68 of 107 women (64%) when based on antenatal bacterial cultures (p=0.54).

  • Six diagnostic accuracy studies (n=55 to n=968) reported that Xpert GBS is a sensitive test that has the potential to help identify GBS colonisation in pregnant women. None investigated the impact of the test on antibiotic prescribing.

  • The version of Xpert GBS used in each of these diagnostic accuracy studies was not clear.

Technical factors

  • The assay detects GBS from combined vaginal and rectal swab specimens and results are given in 50 minutes or less, compared with 24–48 hours for conventional bacterial culture techniques.

Cost and resource use

  • The GeneXpert system is needed to run the Xpert GBS test. This costs between £17,602 and £118,119 depending on the module configurations. The individual test cartridges cost £38.80.

  • No economic studies identified were generalisable to current NHS practice.