What are the treatment options for Group B Streptococcus (GBS) in the vagina during pregnancy?

Treatment of Group B Streptococcus (GBS) Vaginal Colonization During Pregnancy

All pregnant women should be screened for GBS at 35-37 weeks of gestation (or 36 0/7-37 6/7 weeks per ACOG), and those who test positive must receive intravenous penicillin G during labor starting at least 4 hours before delivery. 1, 2

Screening Protocol

When to Screen:

• Universal screening at 35-37 weeks of gestation for all pregnant women 1
• ACOG updated this to 36 0/7-37 6/7 weeks of gestation 2

How to Screen:

• Collect swabs from the lower vagina (vaginal introitus) followed by the rectum using the same swab or two different swabs 1
• Do NOT use a speculum and do NOT collect cervical cultures 1
• Place swabs in non-nutritive transport medium (Amies or Stuart's media without charcoal) 1
• Laboratory should use selective broth medium (SBM or Lim broth) with overnight incubation, then subculture onto blood agar 1

Who Receives Intrapartum Antibiotic Prophylaxis

Automatic Treatment (No Screening Needed):

• Previous infant with invasive GBS disease 1
• GBS bacteriuria at any time during current pregnancy (any colony count) 1

Treatment Based on Screening:

• Positive GBS vaginal-rectal culture at 35-37 weeks 1
• Unknown GBS status at labor onset PLUS any of: delivery <37 weeks, membrane rupture ≥18 hours, or temperature ≥100.4°F (≥38.0°C) 1

No Treatment Needed:

• Negative screening culture in late gestation, regardless of risk factors 1
• Planned cesarean delivery before labor onset with intact membranes, regardless of GBS status 1
• Previous pregnancy with positive GBS (does not predict current pregnancy status) 1

Intrapartum Antibiotic Regimens

First-Line Treatment:

• Penicillin G 5 million units IV initially, then 2.5-3 million units IV every 4 hours until delivery 1
• Penicillin G is preferred over ampicillin due to narrower spectrum and less antibiotic resistance selection 1

Alternative for Non-Allergic Patients:

• Ampicillin 2 g IV initially, then 1 g IV every 4 hours until delivery 1

For Penicillin-Allergic Patients (Low Risk of Anaphylaxis):

• Cefazolin 2 g IV initially, then 1 g IV every 8 hours until delivery 3

For Penicillin-Allergic Patients (High Risk of Anaphylaxis):

• Clindamycin 900 mg IV every 8 hours until delivery (if susceptibility confirmed) 1, 3
• Erythromycin 500 mg IV every 6 hours until delivery (if susceptibility confirmed) 1
• Vancomycin 1 g IV every 12 hours until delivery if GBS resistance to clindamycin/erythromycin or susceptibility unknown 3

Critical Timing Considerations

Effectiveness of Prophylaxis:

• Penicillin G must be administered at least 4 hours before delivery for maximum effectiveness 3
• Even 2 hours of antibiotic exposure reduces GBS vaginal colony counts and decreases clinical neonatal sepsis 2
• Prophylaxis reduces early-onset GBS disease from 4.7% to 0.4% when given appropriately 4
• Do NOT delay necessary obstetric interventions solely to achieve 4 hours of antibiotic administration 2

What NOT to Do

Prenatal Treatment is Ineffective:

• Do NOT use oral antibiotics during pregnancy to eradicate GBS colonization 1
• Prenatal antibiotic treatment does not eliminate carriage and recolonization is typical 1
• Antibiotics should only be given during the intrapartum period 1

Exception for GBS Bacteriuria:

• Women with symptomatic or asymptomatic GBS urinary tract infection should be treated according to standard UTI protocols during pregnancy 1
• They still require intrapartum prophylaxis regardless of prenatal treatment 1

Common Pitfalls

Anaphylaxis Risk:

• The greatest risk with penicillin is anaphylactic reaction (approximately 5 per 10,000 treatments) with severe consequences for mother and child 4
• Carefully document penicillin allergy history and choose prophylaxis accordingly 4
• Avoid antibiotic prophylaxis if mother has history of anaphylaxis to any cause 4

Colonization is Transient:

• GBS colonization can be transient, chronic, or intermittent 1
• Colonization early in pregnancy does NOT predict neonatal sepsis 1
• This is why screening at 35-37 weeks (not earlier) is the standard 1

Impact of Prevention:

• Universal screening and intrapartum prophylaxis reduced early-onset GBS disease incidence by 70% in the 1990s, from 2-3 cases per 1,000 live births to 0.5 per 1,000 1
• Intrapartum prophylaxis prevented an estimated 4,500 early-onset cases and 225 deaths in 1999 alone 1