Group B streptococcus in pregnancy

Definition

• Group B streptococci (Streptococcus agalactiae) are gram-positive bacteria that frequently colonise the genital and gastrointestinal tract asymptomatically.

Classification

• Early-onset disease: it affects newborns in the first 7 days of life.
• Late-onset disease: it occurs from day 7 to day 89 of life.

Occurrence & epidemiology

Why It Matters

• The pathogen: Streptococcus agalactiae (group B).
• Occurrence: colonisation in 10–30% of pregnant women.
• The risk for the infant: early-onset sepsis with pneumonia/meningitis.

Epidemiology

• Up to one third of pregnant women are colonised in the gastrointestinal tract and vagina.

Aetiopathogenesis

Aetiology and pathogenesis

• Early-onset disease arises from vertical transmission during birth, including ascending spread from the vagina.
• The main risk factor is maternal colonisation; the risk also rises with prolonged rupture of membranes and preterm birth.

Clinical features

Clinical features and complications

• In the newborn, both forms present as bacteraemia, sepsis, pneumonia and meningitis; neurological sequelae include loss of sight or hearing and cerebral palsy.
• In the pregnant woman, group B streptococci can cause asymptomatic bacteriuria, urinary tract infection, chorioamnionitis, postpartum endometritis and bacteraemia; preterm birth and stillbirth have also been described.

Diagnosis

• Detection of group B streptococci requires correct specimen collection; besides culture, nucleic acid amplification tests (NAAT) are used.
• Colonisation can change: up to 40% of those testing positive during pregnancy are negative at the time of birth.

Keep learning in the app

Further reading (selection)

1. CDC: Clinical Overview of Group B Strep Disease
2. StatPearls: Group B Streptococcus and Pregnancy (NCBI Bookshelf)
3. DocCheck Flexikon, Streptococcus agalactiae

Cross-references