What is the recommended screening and treatment for Group B streptococcus (Streptococcus agalactiae) in pregnant women?

Screening and Treatment for Group B Streptococcus in Pregnancy

Universal screening for Group B Streptococcus (GBS) should be performed for all pregnant women at 36 0/7 to 37 6/7 weeks of gestation, with intrapartum antibiotic prophylaxis administered to all GBS-positive women during labor to prevent early-onset neonatal GBS disease. 1

Screening Recommendations

• All pregnant women should undergo vaginal-rectal screening for GBS colonization between 36 0/7 and 37 6/7 weeks of gestation (updated from previous recommendation of 35-37 weeks) 2, 1

• Proper specimen collection is critical and involves:

  • Swabbing the lower vagina (2 cm into the vagina) and rectum (1 cm into the anus) using the same swab or two different swabs 3, 4
  • Specimens should be placed in a non-nutritive transport medium (e.g., Amies or Stuart's without charcoal) 3
  • Specimen labels should clearly identify that they are for GBS culture 3
  • Collection can be performed by either the healthcare provider or the patient with appropriate instruction 3, 4

• Women with GBS bacteriuria in any concentration during the current pregnancy do not require additional screening as they are considered GBS colonized 3

• Women who previously gave birth to an infant with invasive GBS disease do not require screening as they should automatically receive intrapartum prophylaxis 3

Indications for Intrapartum Antibiotic Prophylaxis (IAP)

IAP should be administered to women with:

• Positive GBS vaginal-rectal screening culture in current pregnancy 3
• GBS bacteriuria during any trimester of the current pregnancy (regardless of concentration) 3
• Previous infant with invasive GBS disease 3
• Unknown GBS status at the onset of labor (culture not done, incomplete, or results unknown) AND any of the following risk factors:
  • Delivery at <37 weeks' gestation
  • Amniotic membrane rupture ≥18 hours
  • Intrapartum temperature ≥100.4°F (≥38.0°C) 3

Situations Where IAP is NOT Indicated

• Colonization with GBS during a previous pregnancy (unless another indication is present in current pregnancy) 3
• Negative vaginal and rectal GBS screening culture in late gestation during the current pregnancy, regardless of intrapartum risk factors 3
• Cesarean delivery performed before onset of labor on a woman with intact amniotic membranes, regardless of GBS colonization status or gestational age 3

Recommended Antibiotic Regimens

• First-line agent: Intravenous penicillin G (5 million units initially, then 2.5 million units every 4 hours until delivery) 3
• Acceptable alternative: Intravenous ampicillin (2 g initially, then 1 g every 4 hours until delivery) 3
• For women with penicillin allergy:
  • Non-severe allergy: Cefazolin is recommended 2
  • Severe allergy (anaphylaxis, angioedema, respiratory distress, urticaria): Clindamycin or vancomycin based on susceptibility testing 2
  • Penicillin allergy testing is recommended during pregnancy as confirmation or delabeling can provide both short and long-term health benefits 2

Management of Preterm Labor and Premature Rupture of Membranes

• Women admitted with signs and symptoms of preterm labor (<37 weeks) should be screened for GBS colonization at hospital admission unless a vaginal-rectal GBS screen was performed within the preceding 5 weeks 3
• Women with preterm labor and unknown GBS status should receive GBS prophylaxis at hospital admission 3
• For women with threatened preterm delivery, follow the algorithm:
  • Obtain vaginal-rectal swab for GBS culture and start GBS prophylaxis
  • If patient enters true labor, continue prophylaxis until delivery
  • If not in true labor, discontinue prophylaxis and obtain culture results
  • If culture is positive, provide GBS prophylaxis at onset of true labor 3

Special Considerations

• Antibiotics given for GBS prophylaxis to a woman with preterm labor should be discontinued immediately if it's determined she is not in true labor 3
• Women with GBS in the urine should be treated at term with antibiotic prophylaxis regardless of the colony count 4
• GBS-positive women with preterm premature rupture of membranes after 34 weeks are not candidates for expectant management due to higher rates of neonatal infectious complications 4
• Oral antimicrobial agents should not be used before the intrapartum period to eradicate GBS genitorectal colonization, as such treatment is not effective in eliminating carriage or preventing neonatal disease 3

Impact on Neonatal Outcomes

• Early-onset GBS disease incidence has decreased from 0.37 cases per 1,000 live births in 2006 to 0.23 in 2015 due to effective screening and prophylaxis 3
• Despite these improvements, GBS remains a leading cause of neonatal sepsis and meningitis 2, 5
• Preterm infants (<37 weeks) have a 19% case fatality rate compared with 2% in term infants 3
• Intrapartum antibiotic prophylaxis is effective in preventing early-onset GBS disease but does not prevent late-onset disease 2

By following these evidence-based screening and treatment protocols, the risk of early-onset GBS disease can be significantly reduced, improving neonatal outcomes.