What are the guidelines for screening and treatment of Strep (Streptococcus) agalactiae, also known as Group B Streptococcus (GBS), in pregnant women?

Group B Streptococcus (GBS) Screening and Treatment in Pregnancy

All pregnant women should undergo universal GBS screening via vaginal-rectal culture at 36 0/7 to 37 6/7 weeks of gestation, and those who test positive should receive intrapartum antibiotic prophylaxis to prevent early-onset GBS disease in newborns. 1

Indications for GBS Screening

• Universal screening between 36 0/7 and 37 6/7 weeks of gestation (updated from previous 35-37 weeks recommendation) 1, 2
• Proper specimen collection technique:
  • Swab should go 2 cm into the vagina and 1 cm into the anus 3
  • Patient self-collection is acceptable 3

Indications for Intrapartum Antibiotic Prophylaxis (IAP)

IAP is indicated for:

• 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:
  • Delivery at <37 weeks' gestation
  • Rupture of membranes ≥18 hours
  • Intrapartum temperature ≥100.4°F (≥38.0°C)
  • Positive intrapartum nucleic acid amplification test (NAAT) for GBS 4, 5

IAP is NOT indicated for:

• Negative GBS screening culture in current pregnancy (regardless of intrapartum risk factors)
• Planned cesarean delivery before labor onset with intact membranes (regardless of GBS status)
• GBS colonization in previous pregnancy without risk factors in current pregnancy 4

Management of Preterm Labor and Premature Rupture of Membranes

For women with signs/symptoms of preterm labor (<37 weeks):

1. Obtain vaginal-rectal swab for GBS culture at admission (unless done within previous 5 weeks)
2. Start GBS prophylaxis immediately
3. If true labor is confirmed, continue prophylaxis until delivery
4. If not in true labor, discontinue prophylaxis and:
   • If culture is positive: provide IAP when true labor begins
   • If culture is negative: no IAP needed
   • If results unavailable: repeat culture at 35-37 weeks if still pregnant 4

Recommended 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 5

For penicillin-allergic patients:

• Cefazolin: 2 g IV initial dose, then 1 g IV every 8 hours (if no history of anaphylaxis)
• Clindamycin: 900 mg IV every 8 hours (only if GBS isolate is confirmed susceptible)
• Vancomycin: 15-20 mg/kg IV every 12 hours (if GBS susceptibility unknown or resistant to clindamycin) 5

Note: Erythromycin is no longer recommended due to increasing resistance 5

Management of Penicillin Allergy

• Penicillin allergy testing is recommended during pregnancy 2, 3
• Benefits include both short-term (appropriate GBS prophylaxis) and long-term health benefits 2

Special Considerations

• Although 4+ hours of antibiotic prophylaxis is optimal, even 2 hours of exposure reduces GBS vaginal colony counts and decreases clinical neonatal sepsis 1
• Obstetric interventions should not be delayed solely to provide 4 hours of antibiotic administration 1
• Women with GBS in urine should receive IAP regardless of colony count 3
• 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 3

Prevention of Late-Onset GBS Disease

• Currently, there is no approach for prevention of GBS late-onset disease 2
• Research on GBS vaccines continues 3

Common Pitfalls to Avoid

1. Screening too early (before 36 weeks) or too late (after 37 6/7 weeks)
2. Improper specimen collection technique
3. Failing to provide IAP for women with GBS bacteriuria regardless of colony count
4. Using erythromycin for GBS prophylaxis (no longer recommended)
5. Delaying necessary obstetric interventions solely to complete 4 hours of antibiotic prophylaxis
6. Administering IAP for planned cesarean delivery with intact membranes

Despite advances in prevention strategies, GBS remains a significant cause of neonatal morbidity and mortality, requiring continued vigilance from obstetric providers 3.