Treatment of Group B Streptococcus Urinary Tract Infection
For non-pregnant adults with GBS UTI, ampicillin 500 mg orally every 8 hours for 3-7 days is the first-line treatment, while pregnant women with any concentration of GBS bacteriuria require intrapartum antibiotic prophylaxis during labor regardless of whether the UTI itself is treated. 1, 2
Critical Distinction: Pregnancy Status Determines Management
Non-Pregnant Adults
- Ampicillin 500 mg orally every 8 hours for 3-7 days is the preferred first-line therapy for uncomplicated GBS UTI 1
- Amoxicillin 500 mg orally every 8 hours can be used as an alternative with similar efficacy 1
- For complicated UTIs or severe infections requiring IV therapy, ampicillin 150-200 mg/kg/day IV in divided doses every 3-4 hours should be administered 3
- Penicillin G is also highly effective as it remains the gold standard for GBS infections due to its narrow spectrum and high efficacy 4
Pregnant Women: A Different Paradigm
- Any concentration of GBS in urine during pregnancy mandates intrapartum antibiotic prophylaxis during labor, regardless of colony count 2
- GBS bacteriuria at any point in pregnancy indicates heavy genital tract colonization and increases risk for early-onset neonatal disease 2
- The recommended intrapartum regimen is penicillin G 5 million units IV initially, then 2.5-3.0 million units IV every 4 hours until delivery, OR ampicillin 2 g IV initially, then 1 g IV every 4 hours until delivery 2
- This approach is 78% effective in preventing early-onset GBS disease in newborns 2
Important caveat: Treating asymptomatic GBS bacteriuria in non-pregnant patients is unnecessary and promotes antibiotic resistance 2. The distinction between colonization and true infection must be made carefully.
Penicillin-Allergic Patients: Risk-Stratified Approach
Non-Severe Penicillin Allergy
- Cefazolin 2 g IV initial dose, then 1 g IV every 8 hours is the preferred alternative 1, 2
- Cephalexin can also be used for oral therapy 4
Severe Penicillin Allergy or Anaphylaxis Risk
- Clindamycin 900 mg IV every 8 hours OR 300-450 mg orally every 6 hours is recommended ONLY if the GBS isolate is confirmed susceptible through antimicrobial susceptibility testing 1, 2
- Approximately 20% of GBS isolates are resistant to clindamycin, making susceptibility testing mandatory before use 2, 4
- Testing for inducible clindamycin resistance is necessary for isolates susceptible to clindamycin but resistant to erythromycin 2, 4
- Vancomycin may be considered for severe infections when susceptibility results are unavailable 4
Duration of Therapy
- Uncomplicated UTIs: 3-7 days 1
- Complicated UTIs: 5-7 days 1
- Severe infections or bacteremia: 10-14 days 1
- All GBS infections should be treated for a minimum of 10 days to prevent acute rheumatic fever or acute glomerulonephritis 3, 5
Essential Clinical Considerations
Diagnostic Confirmation
- Obtain urine culture before initiating therapy to confirm diagnosis and guide treatment 1
- Significant bacteriuria is defined as ≥50,000 CFUs/mL of a single urinary pathogen 1
- GBS should not be dismissed as a contaminant when isolated in urine culture, as it represents 5.1% of pregnancy-related UTIs 6
Monitoring and Follow-up
- Consider follow-up urine culture after completion of treatment to ensure eradication, especially in complicated cases 1
- For complicated or recurrent infections, evaluation for structural abnormalities of the urinary tract may be indicated 1
Common Pitfalls to Avoid
- Never use fluoroquinolones in pregnant patients 1
- Never use clindamycin without susceptibility testing due to 20% resistance rates 2, 4
- Never fail to provide intrapartum prophylaxis to pregnant women with any GBS bacteriuria, as this increases neonatal mortality risk 2
- Underdosing or premature discontinuation leads to treatment failure and recurrence 2, 4
- Do not treat asymptomatic GBS bacteriuria in non-pregnant patients, as this promotes antibiotic resistance 2