Clinical Practice Guidelines Antenatal Care — Module II
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- Prevalence and incidence
- Risks associated with Group B streptococcus colonisation during pregnancy
- Preventing Group B streptococcus
- Benefits and harms of preventive approaches
- Timing of antenatal screening
- Type of antenatal screening test
- Discussing Group B streptococcus
- Practice summary: Group B streptococcus
9.4Group B streptococcusIdentifying women who are at risk of having a baby with Group B streptococcus enables treatment to be given during labour to prevent transmission of infection to the baby. BackgroundGroup B streptococcus is a common bacterium that can colonise people of all ages without symptoms. It is generally found in the gastrointestinal tract, vagina and urethra. The bacteria can be passed from mother to baby during labour and lead to infection in the first week of life (early onset infection). Late onset infection can develop up to 3 months of age. Prevention focuses on early onset, which is the most common cause of serious infection in newborn babies. Prevalence and incidenceMaternal colonisation: A systematic review estimated rates of maternal colonisation in Europe to range from 6.5% to 36% (Barcaite et al 2008; 2012), with one-third of included studies reporting rates greater than 20%. Lower level studies in Europe and other regions have found similar rates (Whitney et al 2004; Chohan et al 2006; Valkenburg-van den Berg et al 2006; Busetti et al 2007; Konrad & Katz 2007; Hakansson 2008; Jahromi 2008; Rausch et al 2009; Hong et al 2010; Lee et al 2010; Kunze 2011; Yu et al 2011). Australian studies have identified colonisation rates in the range of 20% to 24% (Hiller et al 2005; Angstetra et al 2007). A study of antenatal care for Aboriginal and Torres Strait Islander women in Townsville (n=456) identified Group B streptococcus as a complication of pregnancy in 15.2% of women (Panaretto et al 2006), with a screening rate of around 60% (Panaretto et al 2006; 2007). Group B streptococcus infection in the newborn: The incidence of neonatal Group B streptococcus infection ranges from 0.2/1,000 live births to 1.71/1,000 live births (Ali 2004; Kenyon et al 2004; Mifsud et al 2004; Trotman & Bell 2006; Berardi et al 2007; Konrad & Katz 2007; Trijbels-Smeulders et al 2007; Carbonell-Estrany et al 2008; Berardi et al 2010; Vergnano et al 2010; Kunze 2011; Yu et al 2011). Risk factors: Risk factors for early onset Group B streptococcus infection of the newborn include maternal colonisation during the pregnancy, previous infant with Group B streptococcus infection, preterm birth, prolonged rupture of the membranes and maternal fever during labour (Ohlsson & Shah 2009). There is low-level evidence that Group B streptococcus colonisation in a previous pregnancy may be a risk factor for recolonisation in a subsequent pregnancy (Cheng et al 2008; Turrentine & Ramirez, 2008; Tam et al 2012) but this association was not found in all studies (Weintraub et al 2011). HIV infection does not appear to increase the risk of colonisation (Shah et al 2011). Risks associated with Group B streptococcus colonisation during pregnancyA positive result for Group B streptococcus on urine culture may be a risk factor for preterm labour, premature rupture of the membranes, intrapartum fever and chorioamnionitis (Kessous et al 2012). Early onset Group B streptococcus may affect babies before birth and increase the risk of preterm birth or caesarean section (Tudela et al 2012). In the newborn, the infection is usually evident as respiratory disease, general sepsis, or meningitis within the first week after birth. Population-based surveillance in the United States suggests a neonatal death rate of around 5% of affected babies (CDC 2012). Preventing Group B streptococcusIntravenous antibiotic treatment during labour has been shown to prevent early onset Group B streptococcus infection in 86–89% of newborns of colonised mothers (Lin et al 2001; Schrag et al 2002). Preventive approaches involve offering treatment to all women with a previous infant with Group B streptococcus infection and to other women based on: colonisation as identified by routine antenatal culture of vaginal-rectal swabs: recommended in the United States (Verani et al 2010; Cagno et al 2012; Randis & Polin 2012) and Canada (SOGC 2004); or risk factors for transmission during labour (preterm birth, maternal body temperature >38°C, membrane rupture > 18 hours): recommended in the United Kingdom (NICE 2008; RCOG 2012). Both routine antenatal screening and risk-based treatment approaches are currently used in Australia. Summary of the evidenceBenefits and harms of preventive approachesWhile there is no high level evidence on the benefits of approaches to prevent transmission of Group B streptococcus, prospective and retrospective studies have identified reductions in the incidence of Group B streptococcus in the newborn associated with both routine antenatal screening (Angstetra et al 2007; Chen et al 2005; Eberly & Rajnik, 2009; Phares et al 2008; Puopolo et al 2005) and risk-based screening (Trijbels-Smeulders et al 2007). Narrative reviews have identified limitations associated with routine antenatal screening including a lack of predictive certainty that a positive Group B streptococcus culture will lead to infection of the newborn, the potential for a false negative result and maternal anxiety (Daley & Garland 2004; Konrad & Katz 2007; Berardi et al 2010). Both preventive approaches increase exposure of mother and baby to antibiotics, with possible harmful effects (eg allergic reactions, increase in drug-resistant organisms) (Ohlsson & Shah 2009). However, anaphylaxis following penicillin treatment is rare (4/10,000–4/100,000 women with no known allergy) and the risk is greatly offset by the reduced incidence of neonatal and maternal sepsis (Schrag et al 2002). Recommendation 24 Grade C Offer either routine antenatal screening for Group B streptococcus colonisation or a risk factor-based approach to prevention, depending on organisational policy.
Cost-effectivenessIn the United Kingdom, available modelling on cost-effectiveness does not support introducing routine antenatal screening (Colbourn et al 2007; Kaambwa et al 2010). A French study found that PCR screening during the birth was associated with lower hospital costs than antenatal screening (El Helali et al 2012). No Australian evidence on the cost-effectiveness of approaches to preventing early onset Group B streptococcus was identified in the systematic literature review. An economic analysis carried out to inform the development of these Guidelines (see Appendix E) found that the benefits of screening do not outweigh the costs involved, whatever approach is taken. This is because of the relatively low number of newborns affected and the absence of robust data on severe or long-term health effects in the event of an infection. Of the strategies evaluated, routine screening only is slightly more cost-effective than routine screening with treatment for certain risk factors, when compared to ‘doing nothing’. Timing of antenatal screeningA systematic review (Valkenburg-van den Berg et al 2010) into the optimal timing of antenatal screening found cultures collected in late pregnancy had a high positive predictive value for colonisation during labour. These findings are supported by other smaller studies (Hiller et al 2005; Towers et al 2010). Recommendation 25 Grade B If offering antenatal screening for Group B streptococcus, arrange for testing to take place at 35–37 weeks gestation.
Self-collection of vaginal-rectal specimens has been found to have similar culture yields to collection by a health professional (Arya et al 2008; Hicks & Diaz-Perez 2009; Price et al 2006), without the need for standardised or lengthy information about specimen collection methods (Hicks & Diaz-Perez 2009). Recommendation 26 Grade C Encourage women to self-collect vaginal-rectal specimens for culture testing for Group B streptococcus and offer information about how to do this. Organisational practiceProspective studies evaluating the effects of introducing routine antenatal screening have found that, although screening had been extensively and successfully adopted, early onset Group B streptococcal infection still occurred due to culture detection failure, deviation from protocol (Berardi et al 2010) or missed screening (Van Dyke et al 2009; Faro et al 2010). This highlights the importance of consistently following organisational protocols and auditing outcomes. Discussing Group B streptococcusDiscussion about Group B streptococcus should take place at around 35 weeks gestation so that women have received information about preventive treatment before they go into labour. This timing also enables testing at 35–37 weeks and receipt of test results, if screening is being offered. Points for discussion include: Group B streptococcus is part of the normal bacteria that live in the body and anyone can become colonised with Group B streptococcus without having symptoms; Group B streptococcus is transmitted to the baby during the birth in 1–2 per 1,000 live births and can cause serious infection in the newborn; treatment with intravenous antibiotics during labour reduces the risk of transmission of the infection to the baby; and women may be advised to remain in hospital for at least 24 hours after the birth so that the baby can be observed for signs of Group B streptococcus infection.
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