Identifying 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.
Group 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.
39.1.1 Prevalence and incidence
- Maternal colonisation: A systematic review estimated rates of maternal colonisation in Europe to range from 6.5% to 36% Barcaite et al 2008, Barcaite et al 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 , with a testing rate of around 60% Panaretto et al 2006, Panaretto et al 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 . 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 . HIV infection does not appear to increase the risk of colonisation .
39.1.2 Risks associated with Group B streptococcus colonisation during pregnancy
- A 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 .
- Early onset Group B streptococcus may affect babies before birth and increase the risk of preterm birth or caesarean section . 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.
39.2 Preventing Group B streptococcus
Intravenous antibiotic treatment during labour has been shown to prevent early onset Group B streptococcus infection in 86–89% of newborns of mothers colonised before birth 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 testing and risk-based treatment approaches are currently used in Australia.
39.2.1 Benefits and harms of preventive approaches
While 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 testing Angstetra et al 2007, Chen et al 2005, Eberly & Rajnik 2009, Phares et al 2008, Puopolo et al 2005 and risk-based testing.
Narrative reviews have identified limitations associated with routine antenatal testing 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). 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 .
Offer either routine antenatal testing for Group B streptococcus colonisation or a risk factor-based approach to prevention, depending on organisational policy.
Approved by NHMRC in June 2014; expires June 2019 UNDER REVIEW
In the United Kingdom, available modelling on cost-effectiveness does not support introducing routine antenatal testing Colbourn et al 2007, Kaambwa et al 2010. A French study found that PCR testing during the birth was associated with lower hospital costs than antenatal testing. 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 separate document on economic analyses) found that the benefits of testing 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 testing only is slightly more cost-effective than routine testing with treatment for certain risk factors, when compared to ‘doing nothing’.
39.2.3 Timing of antenatal testing
A systematic reviewinto the optimal timing of antenatal testing 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.
If offering antenatal testing for Group B streptococcus, arrange for testing to take place at 35–37 weeks gestation.
Approved by NHMRC in June 2014; expires June 2019 UNDER REVIEW
39.2.4 Type of antenatal test
Detection rates of Group B streptococcus are higher when a combined vaginal-rectal swab is taken Kovavisarach et al 2007, Daniels et al 2009, Verani et al 2010, RANZCOG 2011, with a sensitivity of 84% compared to 58% for a vaginal swab and 71% for a rectal swab. Limited low-level evidence suggests vaginal-perianal swabs may be an alternative to vaginal-rectal swabs as culture yields are similar and collection causes less discomfort to the woman Jamie et al 2004, Trappe et al 2011.
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.
Encourage women to self-collect vaginal-rectal specimens for culture testing for Group B streptococcus and offer information about how to do this.
Approved by NHMRC in June 2014; expires June 2019 UNDER REVIEW
39.2.5 Organisational practice
Prospective studies evaluating the effects of introducing routine antenatal testing have found that, although testing had been extensively and successfully adopted, early onset Group B streptococcal infection still occurred due to culture detection failure, deviation from protocolor missed testing Van Dyke et al 2009, Faro et al 2010. This highlights the importance of consistently following organisational protocols and auditing outcomes.
39.3 Discussing Group B streptococcus
Discussion 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 testing 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
- 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.
39.4 Practice summary: Group B streptococcus
At around 35 weeks gestation.
- Aboriginal and Torres Strait Islander Health Practitioner
- Aboriginal and Torres Strait Islander Health Worker
- multicultural health worker.
- Discuss prevention
Explain that treatment during labour is offered to women who are identified as being colonised with Group B streptococcus, have previously had a baby with Group B streptococcus infection and/or have risk factors for transmission during labour.
- If testing is offered, give information about the test
Discuss how the test is carried out and, unless the woman would prefer to have the specimen collected by a health professional, provide the test for her to carry out in the health care setting or at home. For women who choose to self-collect, provide clear explanation of how this is done (eg using diagrams or pictures).
- Take a holistic approach
Explain the implications of a positive test result or a previous baby with Group B streptococcus (eg a woman may not be able to give birth in the setting she had planned, treatment may not be possible if labour is very short). If a woman needs to travel to give birth, explain the importance of the test being carried out at 35–37 weeks (ie she needs to plan to have the test before she travels or arrange to have it where she will give birth).
- Document and follow-up
If antenatal testing is carried out, tell the woman the results and note them in her antenatal record. Have a system in place so that a woman with a positive test result or a previous infant with Group B streptococcus infection is informed about the importance of relaying this information to the health professionals who will care for her during labour.
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