A rapid intrapartum test for group B Streptococcus to reduce antibiotic usage in mothers with risk factors: the GBS2...

Mother-to-baby transmission of group B Streptococcus (Streptococcus agalactiae) is the main cause of early-onset infection.

We investigated if intrapartum antibiotic prophylaxis directed by a rapid intrapartum test reduces maternal and neonatal antibiotic use, compared with usual care (i.e. risk factor-directed antibiotics), among women with risk factors for vertical group B Streptococcus transmission, and examined the accuracy and cost-effectiveness of the rapid test.

An unblinded cluster randomised controlled trial with a nested test accuracy study, an economic evaluation and a microbiology substudy.

UK maternity units were randomised to either a strategy of rapid test or usual care.

Vaginal and rectal swabs were taken from women with risk factors for vertical group B Streptococcus transmission in established term labour. The accuracy of the GeneXpert^® Dx IV GBS rapid testing system (Cepheid, Maurens-Scopont, France) was compared with the standard of selective enrichment culture in diagnosing maternal group B Streptococcus colonisation.

Primary outcomes were rates of intrapartum antibiotic prophylaxis administered to prevent early-onset group B Streptococcus infection and accuracy estimates of the rapid test. Secondary outcomes were maternal antibiotics for any indication, neonatal antibiotic exposure, maternal antibiotic duration, neonatal group B Streptococcus colonisation, maternal and neonatal antibiotic resistance, neonatal morbidity and mortality, and cost-effectiveness of the strategies.

Twenty-two maternity units were randomised and 20 were recruited. A total of 722 mothers (749 babies) participated in rapid test units and 906 mothers (951 babies) participated in usual-care units. There were no differences in the rates of intrapartum antibiotic prophylaxis for preventing early-onset group B Streptococcus infection in the rapid test units (41%, 297/716) compared with the usual-care units (36%, 328/906) (risk ratio 1.16, 95% confidence interval 0.83 to 1.64). There were no differences between the groups in intrapartum antibiotic administration for any indication (risk ratio 0.99, 95% confidence interval 0.81 to 1.21). Babies born in the rapid test units were 29% less likely to receive antibiotics (risk ratio 0.71, 95% confidence interval 0.54 to 0.95) than those born in usual-care units. The sensitivity and specificity of the rapid test were 86% (95% confidence interval 81% to 91%) and 89% (95% confidence interval 85% to 92%), respectively. In 14% of women (99/710), the rapid test was invalid or the machine failed to provide a result. In the economic analysis, the rapid test was shown to be both less effective and more costly and, therefore, dominated by usual care. Sensitivity analysis indicated potential lower costs for the rapid test strategy when neonatal costs were included. No serious adverse events were reported.

The Group B Streptococcus 2 (GBS2) trial found no evidence that the rapid test reduces the rates of intrapartum antibiotic prophylaxis administered to prevent early-onset group B Streptococcus infection. The rapid test has the potential to reduce neonatal exposure to antibiotics, but economically is dominated by usual care. The accuracy of the test is within acceptable limits.

The role of routine testing for prevention of neonatal infection requires evaluation in a randomised controlled trial.

Current Controlled Trials ISRCTN74746075.

This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 26, No. 12. See the NIHR Journals Library website for further project information.