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GBS and Birth

Group B Streptococcus (GBS) is a transient gram-positive commensal microorganism present in approximately 18% of women (95%CI 17%-19%) of childbearing age’s vaginas (Harperhoven et al., 2020). It is the causative agent of GBS sepsis, meningitis and pneumonia. Early-onset group B streptococcal (EOGBS) disease is a leading cause of infant mortality and morbidity particularly in developed countries despite its limited incidence of 0.41 cases per 1000 live births (Berardi et al., 2015). According to McQuaid & Plumb (2015) over 40 babies die annually as a result of EOGBS in the UK. This is in the context of an estimated annual birth rate of 712 000 live births. In Australia pathology screening for GBS is covered under Medicare and bulk billed for privately practicing midwives and is isolated independently of other organisms.

There is significant variation both at the local health district level and globally regarding the best approach to managing EOGBS. These methods include: universal screening for the identification and treatment of GBS, and the identification and management of those who are deemed ‘higher risk’ (prolonged rupture of membranes, febrile in labour, pre term labour, previous bacteriuria). There is a state wide policy for universal screening in NSW.

Since 1996 the CDC has recommended universal screening as the best method of identifying and treating for GBS colonisation (Tucker, 2002). This has arguably been the method that has resulted in the most effective reduction in rates of EOGBS, however Hasperhoven et al (2020)’s systematic review into the evidence around the management found that the number needed to screen compared to risk based protocols was 1874 women. This is significant not only because of the potential for reduced effectiveness of antibiotics as we move towards a post antibiotic era, but also because predelivery antibiotics affect the bacterial population of the birth canal which limits the colonisation of the infant of the mother’s microbes and has been linked to potential outcomes such as asthma, obesity and autoimmune diseases (Ledger & Blaser, 2013). Ledger & Blaser (2013) estimate that greater than 40% of women today are exposed to antibiotics in labour and birth, stating that very few of these infants would have been exposed in utero prior to 1996. Additionally, because of the transient nature of GBS colonisation, many women who test positive at 35 week’s gestation would have naturally processed the flora by the time they birth their baby and conversely 61% of 251 infants with identified EOGBS in a retrospective study had been testing negative during universal screening. Intrapartum antibiotics are also associated with a disruption of transmission of microbiota from mother to infant which is associated with disease later in life (Li et al., 2019)

In 2017, a Danish study (Khalil et al) looked at the validity of using PCR (Polymerase chain reaction) testing to confirm colonisation of GBS in early labour which resulted in the reduction of antibiotics from 12% to 4%. The study also compared the sensitivity and specificity of GBS screening versus GBS PCR testing and found among the 108 women with one or more risk factor, GBS was present in 23%, the test had a sensitivity of 92% (23 out of 25) and a specificity of 89% (74 of 83). Furthermore, of the 12% of women in the study who had risk factors, only 2.7% had a risk factor and tested positive at the time of birth. This could represent substantial overtreatment and misuse of antibiotics when applied to the entire population. The advantage of PCR testing is that it can give results within 2 hours and carries a 99% negative predictive value and 100% positive predictive value compared to traditional culture (Poliquin et al., 2016)

Of significant is the approximately 40% of confirmed cases pf GBS sepsis that have no risk factors when taking a screening-based approach (Kanto, 2009). Additionally, McQuaid & Plumb (2015) found that of those that did develop EOGBS only 19% of those with identifiable risk factors received intrapartum antibiotics. This signifies limitations of determining the effectiveness of both screening and risk based approaches if they are not implemented successfully. 

Homer et al., (2014) found that both risk-based and screening based guidelines were appropriate approaches to care with focus being on widespread implementation of approach leading to effectiveness rather than the sporadic application of therapies seen across studies. Hasperhoven et al., (2020) also recommended that GBS protocols be frequently reviewed to reflect updating evidence particularly around evolving PCR identification which could lead to faster, more accurate identification and reduce unnecessary antibiotic use to the benefit of both mother and baby.

Berardi, A., Ferrari, F., & Facchinetti, F. (2015). Intrapartum antibiotic prophylaxis for Group B Streptococcus and risk of unnecessary antibiotics. American Journal of Obstetrics and Gynaecology 212(3)408-408

Hasperhoven, G, F., Al-Nasiry, S., Bekker, V., Villamor, E., Kramer, B. (2020). Universal Screening Versus Risk-Based Protocols for Antibiotics Prophylaxis during Childbirth to Prevent Early-Onset Group B Streptococcal Disease: A systematic Review and Meta-analysis. BJOG Doi 10.1111/1471-0528.16085

Poliquin, V., Cohen, E., Guillaume Poliquin, P., Schneider, C., & Menticoglou. (2016). Ongoing Cases of Early Onset Group B Streptococcal Disease in the Era of Screening and Prophylaxis. Journal of Obstetrics and Gynaecology Canada 38(10) 926-929

Homer, C., Scarf, V., Catling, C., & Davis, D. (2014). Culture-based versus risk-based screening for the prevention of group B streptococcal disease in newborns: a review of national guidelines. Women Birth (27) 46-51

Khalil, M., Uldbjerg, N., Thorsen, P., Henriksen, B., & Moller, J. (2017). Risk-based screening combined with a PCR-based test for group B streptococci diminishes the use of antibiotics in laboring women. Journal of Obstetrics and Gynaecology and Reproductive Bioliogy (215) 188-192

Ledger, W., & Blaser, M. (2013). Are we using too many antibiotics during pregnancy?. BJOG. 120(12) 1450-1452

Li, H., Xiao, B., Zhang, Y., Xiao, Luo, J., Huang, W. (2019). Impact of maternal intrapartum antibiotics on the initial oral microbiome of neonates. Paediatrics and Neonatology 60(6) 654-661

McQuaid, F., & Plumb, J. (2015). More needs to be done to prevent Group B Strep infection in the UK. BMJ 23(6)

Tucker, M. (2002). CDC seek to expand group B strep testing: New date show universal screening is more effective than the risk-based method (antibiotic resistance a concern). OBGYN News 37(3)

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