What is the recommended treatment for symptomatic Group B Streptococcus (GBS) vaginitis, including alternatives for patients with low‑risk or high‑risk penicillin allergy?

Treatment of Group B Streptococcus (GBS) Vaginitis

GBS vaginal colonization should NOT be treated with antibiotics outside of labor—treatment is ineffective, promotes resistance, and provides no benefit. 1

Critical Distinction: When GBS Treatment IS and IS NOT Indicated

Do NOT Treat (Asymptomatic Vaginal Colonization)

• Oral or intravenous antibiotics given before labor are completely ineffective at eliminating GBS colonization and should never be used for asymptomatic vaginal colonization. 1
• Antimicrobial agents administered before the intrapartum period do not eliminate carriage, do not prevent neonatal disease, and may cause adverse consequences including antibiotic resistance. 2, 1
• This is a common and dangerous error—prescribing oral antibiotics for asymptomatic GBS vaginal colonization during pregnancy is both ineffective and harmful. 1

DO Treat: Two Specific Scenarios Only

1. Symptomatic GBS Urinary Tract Infection (Any Trimester)

• Any concentration of GBS in urine during pregnancy requires immediate treatment according to standard UTI protocols. 1
• GBS bacteriuria at ≥10,000 CFU/mL indicates heavy genital tract colonization and significantly increases risk of early-onset neonatal disease. 1
• Treatment regimens follow standard pregnancy UTI protocols using pregnancy-safe antibiotics based on susceptibility testing. 1
• Critical: Even after treating the UTI, intrapartum IV prophylaxis during labor remains mandatory, as oral antibiotics do not eliminate GBS colonization from the genitourinary tract. 1

2. Intrapartum IV Prophylaxis During Active Labor (All GBS-Positive Women)

• All pregnant women with documented GBS colonization on vaginal-rectal culture at 36 0/7–37 6/7 weeks must receive IV antibiotics during active labor. 1
• Intrapartum prophylaxis administered ≥4 hours before delivery reduces early-onset neonatal GBS disease by 78%. 1

Intrapartum Antibiotic Prophylaxis Regimens

For Women WITHOUT Penicillin Allergy

• Penicillin G 5 million units IV initially, then 2.5–3.0 million units IV every 4 hours until delivery (preferred agent due to narrow spectrum and universal GBS susceptibility). 2, 1
• Ampicillin 2 g IV initially, then 1 g IV every 4 hours until delivery (acceptable alternative, though broader spectrum). 2, 1

For Women WITH Low-Risk Penicillin Allergy

Low-risk allergy = history of rash without systemic symptoms, mild gastrointestinal upset, or reactions NOT including anaphylaxis, angioedema, respiratory distress, or urticaria. 2

• Cefazolin 2 g IV initially, then 1 g IV every 8 hours until delivery (preferred alternative for low-risk allergy). 2, 1, 3
• Cross-reactivity between penicillins and first-generation cephalosporins is approximately 0.1–10%, making cefazolin safe for most penicillin-allergic patients without severe reactions. 3, 4

For Women WITH High-Risk Penicillin Allergy

High-risk allergy = history of anaphylaxis, angioedema, respiratory distress, or urticaria following penicillin or cephalosporin administration. 2, 3

Step 1: Obtain Susceptibility Testing

• Clindamycin and erythromycin susceptibility testing MUST be performed on the prenatal GBS isolate from all penicillin-allergic women at high risk for anaphylaxis. 2, 1, 3
• Testing should include D-zone testing on isolates that are erythromycin-resistant but clindamycin-susceptible to detect inducible clindamycin resistance. 2, 1

Step 2: Select Antibiotic Based on Susceptibility

• If susceptible to both clindamycin and erythromycin: Clindamycin 900 mg IV every 8 hours until delivery. 2, 1, 3
• If resistant to either agent OR susceptibility unknown: Vancomycin 1 g IV every 12 hours until delivery. 2, 1, 3
• Important: Erythromycin is no longer an acceptable alternative for intrapartum GBS prophylaxis. 2, 1

Management of Abnormal Vaginal Discharge

If a patient presents with symptomatic vaginitis (abnormal discharge, odor, irritation):

• Evaluate for other treatable causes such as bacterial vaginosis (Gardnerella, Mobiluncus), candidiasis (yeast infection), or trichomoniasis. 1
• GBS colonization itself does not cause symptomatic vaginitis and should not be treated outside of labor. 1
• Treat the actual pathogen causing symptoms (e.g., metronidazole for bacterial vaginosis, antifungals for candidiasis). 5, 6

Common Pitfalls to Avoid

• Never prescribe oral antibiotics (e.g., amoxicillin, cephalexin) for asymptomatic GBS vaginal colonization detected on routine screening—this is ineffective and promotes resistance. 2, 1
• Do not assume that treating a GBS UTI earlier in pregnancy eliminates the need for intrapartum prophylaxis—recolonization after oral antibiotics is typical, and intrapartum IV prophylaxis remains mandatory. 1
• Do not delay medically necessary obstetric procedures to achieve 4 hours of antibiotic exposure—while 4 hours is optimal, prophylaxis should be given as soon as labor begins. 1
• Do not use cefoxitin or other second-generation cephalosporins—only first-generation cephalosporins (cefazolin) should be used, as cefoxitin resistance has been reported among GBS isolates. 1

Special Pregnancy Scenarios

• Preterm labor (<37 weeks) with GBS colonization: Administer GBS prophylaxis immediately at hospital admission; discontinue if patient is not in true labor. 1
• Preterm premature rupture of membranes (PPROM): Ampicillin 2 g IV once, followed by 1 g IV every 6 hours for at least 48 hours provides both latency support and adequate GBS prophylaxis. 1
• Women with prior infant with invasive GBS disease: Automatically receive intrapartum prophylaxis regardless of current GBS screening results. 1