Treatment of Group B Streptococcus Urinary Tract Infection
For non-pregnant adults with GBS UTI, treat with ampicillin 500 mg orally every 8 hours for 3-7 days, or amoxicillin 500 mg orally every 8 hours as an equally effective alternative. 1
Treatment Algorithm Based on Patient Population
Non-Pregnant Adults (Standard Approach)
First-line therapy:
- Ampicillin 500 mg orally every 8 hours for 3-7 days is the preferred treatment 1
- Amoxicillin 500 mg orally every 8 hours can be substituted with similar efficacy 1
- All GBS strains remain 100% sensitive to penicillin and ampicillin, making these reliable first-line choices 2
For complicated UTIs or severe infections:
- Escalate to ampicillin 18-30 g/day IV in divided doses 1
- Alternatively, penicillin G 5 million units IV initially, then 2.5 million units IV every 4 hours 3
- Extend treatment duration to 10-14 days for bacteremia or severe infections 1
Penicillin-Allergic Patients (Risk-Stratified)
For non-severe penicillin allergies:
- Cefazolin 2 g IV initial dose, then 1 g IV every 8 hours 1, 3
- Cephalexin is an acceptable oral alternative 4
For severe penicillin allergies or anaphylaxis risk:
- Clindamycin 900 mg IV every 8 hours OR 300-450 mg orally every 6 hours ONLY if susceptibility testing confirms susceptibility 1, 3
- This is critical because approximately 20% of GBS isolates are resistant to clindamycin, and up to 77% show resistance in some populations 3, 2
- Vancomycin may be used for severe infections when susceptibility results are unavailable 1, 4
Mandatory susceptibility testing:
- Always perform susceptibility testing before using clindamycin to avoid treatment failure 3, 4
- Test for inducible clindamycin resistance in isolates susceptible to clindamycin but resistant to erythromycin 3, 4
Pregnant Women (Critical Distinction)
This population requires a fundamentally different approach:
- Any concentration of GBS bacteriuria during pregnancy—regardless of colony count—mandates intrapartum antibiotic prophylaxis during labor 5, 3
- GBS bacteriuria at any point in pregnancy is a marker for heavy genital tract colonization and increases risk for early-onset neonatal disease 5, 3
- Treat the acute UTI at time of diagnosis according to standard protocols, AND provide intrapartum prophylaxis during labor 5
Intrapartum prophylaxis regimen:
- Penicillin G 5 million units IV initially, then 2.5-3.0 million units IV every 4 hours until delivery 3
- Alternative: Ampicillin 2 g IV initially, then 1 g IV every 4 hours until delivery 3
- This approach is 78% effective in preventing early-onset GBS disease when administered ≥4 hours before delivery 3
For pregnant patients with penicillin allergy:
- Non-severe allergy: Cefazolin 2 g IV initially, then 1 g IV every 8 hours 3
- Severe allergy/anaphylaxis risk: Clindamycin 900 mg IV every 8 hours (only if susceptible) 3
- Avoid fluoroquinolones in pregnancy 1
Duration of Therapy
- Uncomplicated UTI: 3-7 days 1
- Complicated UTI: 5-7 days 1
- Severe infections or bacteremia: 10-14 days 1
Essential Clinical Considerations
Obtain urine culture before initiating therapy:
- Confirm diagnosis and guide treatment decisions 1
- Significant bacteriuria is defined as ≥50,000 CFUs/mL 1
Distinguish colonization from true infection:
- Avoid treating asymptomatic GBS bacteriuria in non-pregnant patients, as this promotes antibiotic resistance 3
- The exception is pregnancy, where any GBS bacteriuria requires intervention 5, 3
Consider follow-up urine culture:
- Particularly important in complicated cases to ensure eradication 1
- Evaluate for structural urinary tract abnormalities in recurrent or complicated infections 1
Common Pitfalls to Avoid
Underdosing or premature discontinuation leads to treatment failure and recurrence 3, 4
Using clindamycin without susceptibility testing risks treatment failure due to high resistance rates (20-77% depending on population) 3, 2
Failing to provide intrapartum prophylaxis to pregnant women with any GBS bacteriuria increases neonatal mortality risk 3
Do not treat asymptomatic GBS bacteriuria in non-pregnant patients—this is unnecessary and promotes resistance 3