Group B Streptococcal Disease

Group B Streptococcus (Streptococcus agalactiae) is a leading cause of invasive infection across the maternal-fetal-neonatal continuum, including early-onset neonatal sepsis acquired around birth. It is treated as a topic in its own right because of its distinctive epidemiology, its links to maternal genital colonisation, and the prominent role of intrapartum prevention in reducing newborn disease.

Definition

Group B streptococcal disease is invasive infection caused by Streptococcus agalactiae (Lancefield group B), which colonises the maternal genital and gastrointestinal tract and can be transmitted to the infant around birth, causing early-onset disease, and can also cause late-onset disease and infection in pregnant women.

Scope

This entry covers what group B streptococcal disease is, how maternal colonisation relates to neonatal infection, the early- and late-onset presentations in infants, the global burden, and how intrapartum prophylaxis fits into prevention. It is reference content describing the disease and its epidemiology, not a clinical management protocol.

Core questions

• How does maternal colonisation with group B Streptococcus relate to neonatal disease?
• How do early-onset and late-onset group B streptococcal disease differ?
• What is the global burden of group B streptococcal disease across pregnancy and infancy?
• How does intrapartum prophylaxis fit into prevention, and what are its limits?

Key concepts

• Streptococcus agalactiae (Lancefield group B)
• Maternal genital and gastrointestinal colonisation
• Vertical transmission around birth
• Early-onset versus late-onset GBS disease
• Intrapartum antibiotic prophylaxis
• Maternal screening versus risk-based strategies
• Prospects for a group B streptococcal vaccine

Mechanisms

Group B Streptococcus commonly colonises the maternal genital and gastrointestinal tract without causing maternal illness. Around the time of birth the organism can be transmitted vertically to the infant — by ascending infection or during passage through the birth canal — and in susceptible newborns can cause invasive early-onset disease. Late-onset group B streptococcal disease occurs later in infancy and may follow acquisition from the mother or other sources. Intrapartum antibiotic prophylaxis, directed by maternal screening for colonisation or by clinical risk factors, interrupts transmission around delivery and has reduced early-onset disease, although it does not prevent late-onset disease, motivating interest in maternal vaccination.

Clinical relevance

Group B streptococcal disease underpins much of perinatal infection prevention, including maternal screening and intrapartum prophylaxis programmes, and remains a focus of vaccine development. This entry describes the disease and its prevention strategies at a conceptual level; it does not provide screening thresholds or antibiotic regimens for an individual patient, which are governed by current guidelines and the responsible clinicians.

Epidemiology

Group B Streptococcus is estimated to cause a substantial worldwide burden of invasive disease in infants, together with maternal infection, stillbirth, and preterm birth, with the burden falling disproportionately on regions with limited access to prevention. Where intrapartum prophylaxis has been widely implemented, early-onset disease has declined markedly, while late-onset disease has been less affected.

History

Group B Streptococcus emerged as a recognised leading cause of neonatal sepsis in the 1970s. Subsequent decades saw the development of prevention strategies based on maternal screening and intrapartum antibiotic prophylaxis, formalised in successive guidelines, and more recent work has quantified the global burden across the maternal-fetal-neonatal continuum and advanced the case for maternal vaccination.

Debates

Universal screening versus risk-based prophylaxis

Strategies to identify which mothers should receive intrapartum prophylaxis — universal antenatal culture screening versus assessment based on clinical risk factors — have been compared and debated, with implications for how effectively early-onset disease is prevented.

Seminal works

• seale-2017
• verani-2010-clp

Frequently asked questions

Why does group B Streptococcus matter so much in newborns?

It is a leading cause of invasive perinatal infection, including early-onset neonatal sepsis, because it colonises the maternal genital tract and can be transmitted to the infant around birth.

Does intrapartum prophylaxis prevent all group B streptococcal disease?

It substantially reduces early-onset disease acquired around birth but does not prevent late-onset disease, which is one reason maternal vaccines are being developed.