Group B streptococci (GBS) in women

Group B Streptococcus on HVS in non-pregnant woman:

• "Group B streptococcus (GBS) is a vaginal commensal in 10-15% of women. There is no evidence that GBS in isolation increases the risk of PID. Asymptomatic carriers do not require treatment." (1). Note that the National Library for Health (NLH) Women's Specialist Library quotes a rate of carriage as a vaginal commensal of up to 30% (2)

Group B Streptococcus in Pregnancy (2):

Antenatal infection:

• during pregnancy, many women experience symptomatic vaginal discharge, which may prompt health professionals to take a swab for culture. If GBS is detected during the antenatal period, it is important to explain the following to the woman:
• GBS is a normal vaginal commensal in up to 30% of the population
• antenatal treatment with oral penicillin does not reduce the likelihood of GBS colonisation at the time of delivery, and so is not required
• a note of the presence of vaginal carriage should be made in the woman's maternity notes, so health professionals can take appropriate action during labour
• GBS is highly unlikely to be the cause of the vaginal discharge
  
  
• risk of neonatal disease when GBS is detected at 35-37 weeks by swabs taken from the low vagina and rectum and cultured in enrichment medium is around 1 in 500
  
  
• GBS in urine:
  • if GBS is cultured at any time during the current pregnancy, there is a higher risk of neonatal disease
    • possible that detected urinary tract infections indicate a higher level of genital tract GBS carriage. Exact quantification of the risk of neonatal disease is not possible, but in addition to treatment of the urinary infection at the time of diagnosis, after discussion, intrapartum prophylaxis should be offered:
      • intrapartum IV antibiotic prophylaxis should be offered to women with GBS bacteriuria in the current pregnancy
        
        
• preterm premature rupture of the membranes:
  • If GBS is detected on a vaginal swab, antenatal treatment specifically for GBS is not necessary prior to labour. Intrapartum prophylaxis should be considered, especially if labour occurs before 37 weeks

Delivery:

• UK incidence of early-onset neonatal GBS disease is approximately 0.5 per 1000 births. Around 60% of these cases are associated with identifiable risk factors, some of which may arise during labour. Risk factors include:
  • intrapartum fever (>38C)
  • prematurity (<37 weeks)
  • prolonged rupture of the membranes (>18 hours) at term
  • known carriage of GBS
  • previous infant with GBS disease
  • a GBS urinary tract infection during that pregnancy
    
    
• if history of antenatal treated GBS:
  • maternal GBS carriage may be incidentally identified during the antenatal period, for example following a swab for vaginal symptoms. Recolonisation of the genital tract is common following antenatal antibiotics and treatment at this time does not reliably prevent colonisation at the time of labour. If a woman has received antibiotics during the antenatal period following incidental finding of GBS carriage, this does not change the need for antibiotics during labour
    • intrapartum antibiotic prophylaxis should be considered for low risk women who have incidental GBS carriage identified during the antenatal period, even if treated before labour
• NICE state that (3):
  • intrapartum antibiotics
    • offer intrapartum antibiotic prophylaxis using intravenous benzylpenicillin to prevent early onset neonatal infection for women who have had:
      • a previous baby with an invasive group B streptococcal infection
      • group B streptococcal colonisation, bacteriuria or infection in the current pregnancy
        
        
  • advice following pregnancy:
    • when a baby who has had a group B streptococcal infection is discharged from hospital:
      • advise the woman that if she becomes pregnant again:
        • there will be an increased risk of early-onset neonatal infection
        • she should inform her maternity care team that a previous baby has had a group B streptococcal infection
        • antibiotics in labour will be recommended
      • inform the woman's GP in writing that there is a risk of:
        • recurrence of group B streptococcal infection in the baby, and group B streptococcal infection in babies in future pregnancies
    • if the woman has had group B streptococcal colonisation in the pregnancy but without infection in the baby, inform her that if she becomes pregnant again, this will not affect the management of the birth in the next pregnancy.

Reference:

• (1) FFRPHC. For asymptomatic women having routine cervical cytology, does an incidental finding of bacteria on the report need to be treated? 2004 (http://www.ffprhc.org.uk)
• (2) NLH. Women's Health Specialist Library (accessed 25/6/2008)
• (3) NICE (August 2012). Antibiotics for early-onset neonatal infection - Antibiotics for the prevention and treatment of early-onset neonatal infection