What is the recommended treatment for group B strep (Streptococcus agalactiae) in pregnancy?

Treatment of Group B Streptococcus (GBS) in Pregnancy

Intravenous penicillin G (5 million units IV initial dose, then 2.5-3.0 million units IV every 4 hours until delivery) is the first-line treatment for intrapartum prophylaxis of Group B Streptococcus in pregnancy, with ampicillin as an acceptable alternative. 1

Screening and Indications for Treatment

Universal Screening

• All pregnant women should undergo screening for GBS colonization between 36 0/7 and 37 6/7 weeks' gestation (updated from previous recommendation of 35-37 weeks) 1, 2
• Screening involves collecting both vaginal and rectal specimens 3

Indications for Intrapartum Antibiotic Prophylaxis (IAP)

IAP is indicated in the following situations:

• Positive GBS vaginal-rectal screening culture in current pregnancy
• GBS bacteriuria during any trimester of current pregnancy
• Previous infant with invasive GBS disease
• Unknown GBS status at labor onset with 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, 1

When IAP is NOT Indicated

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

Antibiotic Regimens

First-Line Treatment

• Penicillin G: 5 million units IV initial dose, then 2.5-3.0 million units IV every 4 hours until delivery
• Ampicillin: 2 g IV initial dose, then 1 g IV every 4 hours until delivery 1

For Penicillin-Allergic Women

For women with non-anaphylactic penicillin allergy:

• Cefazolin: 2 g IV initial dose, then 1 g IV every 8 hours until delivery

For women with history of anaphylaxis to penicillin:

• Clindamycin: 900 mg IV every 8 hours until delivery (if isolate is susceptible)
• Vancomycin: 1 g IV every 12 hours until delivery (if isolate is resistant to clindamycin or susceptibility unknown) 1

Important Clinical Considerations

Timing of Antibiotics

• Optimal effectiveness requires administration of antibiotics at least 4 hours before delivery 4
• Even if 4 hours cannot be achieved before delivery, IAP should still be initiated as soon as possible 5

Treatment of GBS UTI During Pregnancy

• GBS bacteriuria at any colony count indicates heavy genital tract colonization
• Treat with appropriate antibiotics for UTI (oral amoxicillin is appropriate for outpatient treatment)
• Treatment should continue for 5-7 days for uncomplicated UTIs and 10-14 days for complicated UTIs 1
• Even after treatment, intrapartum antibiotic prophylaxis is still required during labor 1

Common Pitfalls to Avoid

1. Do not treat GBS colonization with oral antibiotics before labor: This is ineffective at eliminating carriage or preventing neonatal disease, as 30-70% of treated women remain colonized at delivery 1

2. Do not use erythromycin for GBS prophylaxis: It is no longer recommended due to increasing resistance and poor placental transfer 1

3. Perform susceptibility testing for penicillin-allergic patients: This is essential due to increasing resistance to alternative antibiotics 1

4. Do not miss opportunities for prophylaxis in preterm labor: Women with threatened preterm delivery should be screened and managed according to specific algorithms 3, 2

5. Do not assume cesarean delivery eliminates need for prophylaxis: IAP is still indicated if labor begins or membranes rupture before cesarean delivery in GBS-positive women 3

The implementation of universal screening and IAP has reduced early-onset GBS disease incidence by more than 80% in the United States, preventing an estimated 70,000 cases between 1994 and 2010 5. However, IAP does not prevent late-onset GBS disease, which typically occurs after the first week of life 2.