What is the recommended treatment for pregnant women with Group B strep (Streptococcus agalactiae) colonization during labor?

Treatment of Group B Streptococcus in Pregnant Women During Labor

Intravenous penicillin G (5 million units IV initial dose, followed by 2.5-3.0 million units IV every 4 hours until delivery) is the recommended first-line treatment for pregnant women with Group B streptococcus colonization during labor. 1

Screening and Identification

• Screen all pregnant women for GBS colonization at 36 0/7 to 37 6/7 weeks of gestation (updated from previous recommendation of 35-37 weeks) 1, 2
• Collect specimens using a single swab of both the lower vagina (2 cm inside vagina) and rectum (1 cm through anal sphincter) 1
• Women can perform their own swabs with proper instruction 3
• Laboratory should use selective broth medium to maximize GBS recovery 4

Indications for Intrapartum Antibiotic Prophylaxis (IAP)

IAP is indicated for women with:

• Positive GBS vaginal/rectal screening culture at 36-37 weeks 1
• GBS bacteriuria at any time during current pregnancy (regardless of colony count) 1, 5
• Previous infant with invasive GBS disease 1, 5
• Unknown GBS status at onset of labor with risk factors:
  • Delivery at <37 weeks' gestation
  • Rupture of membranes ≥18 hours
  • Intrapartum fever ≥100.4°F (≥38.0°C) 4

Recommended Antibiotic Regimens

First-line therapy:

• Penicillin G: 5 million units IV initial dose, then 2.5-3.0 million units IV every 4 hours until delivery 4, 1

Alternative first-line therapy:

• Ampicillin: 2 g IV initial dose, then 1 g IV every 4 hours until delivery 4, 1

For women with penicillin allergy:

• If at low risk for anaphylaxis: Cefazolin 2 g IV initial dose, then 1 g IV every 8 hours until delivery 1
• If at high risk for anaphylaxis (history of anaphylaxis, angioedema, respiratory distress, or urticaria):
  • With known susceptibility: Clindamycin 900 mg IV every 8 hours until delivery (if isolate is susceptible)
  • With unknown susceptibility or resistance: Vancomycin 20 mg/kg IV every 8 hours until delivery 4, 1

Special Situations

Preterm Labor or Premature Rupture of Membranes (PROM)

• For women <37 weeks with unknown GBS status: Administer IAP for at least 48 hours 5
• For GBS-positive women with PROM at ≥37 weeks: Immediate induction of labor with IAP 1, 5
• For GBS-positive women with PROM at <37 weeks: Administer IAP for 48 hours while awaiting labor 5

Planned Cesarean Delivery

• IAP not required for women undergoing planned cesarean delivery before labor onset with intact membranes, regardless of GBS status 1

Chorioamnionitis

• Administer broad-spectrum antibiotics that include coverage for GBS, regardless of GBS status or gestational age 5

Effectiveness and Timing

• Optimal IAP should be administered for at least 4 hours before delivery 2
• Even 2 hours of antibiotic exposure has been shown to reduce GBS vaginal colony counts 2
• IAP has reduced early-onset GBS disease by more than 80% (from 1.8 cases/1000 live births to 0.26 cases/1000 live births) 6
• Effectiveness is high among both term (91%) and preterm (86%) infants when first-line therapy is received for at least 4 hours 6

Important Considerations

• Do not use oral antibiotics to treat GBS colonization during pregnancy as this is ineffective 4
• Obstetric interventions should not be delayed solely to provide 4 hours of antibiotic administration 2
• Penicillin G is preferred over ampicillin due to its narrower spectrum, which reduces the risk of selecting for antibiotic-resistant organisms 4
• The risk of anaphylaxis with penicillin is approximately 5 cases per 10,000 treatments 7
• Penicillin allergy testing has been shown to be safe during pregnancy 3

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