What is the recommended treatment for group B strep (Streptococcus agalactiae) urinary tract infection (UTI)?

Treatment of Group B Streptococcal Urinary Tract Infections

Penicillin G or ampicillin should be used as first-line therapy for Group B Streptococcal (GBS) urinary tract infections due to their narrower spectrum of activity and lower likelihood of selecting for resistant organisms. 1

First-Line Treatment Options

For Non-Pregnant Adults

• Penicillin G: 5 million units IV initially, then 2.5-3.0 million units IV every 4 hours 1
• Ampicillin: 2 g IV initially, then 1 g IV every 4 hours 1
• Oral options (for uncomplicated infections):
  • Amoxicillin: 500 mg orally every 8 hours 1
  • Cephalexin: 500 mg orally every 6 hours 1

Treatment Duration

• Uncomplicated UTIs: 7-10 days 1
• Complicated UTIs or pyelonephritis: 10-14 days 1
• Continue treatment for at least 48-72 hours after symptoms resolve 1

Alternative Options for Penicillin-Allergic Patients

For Non-Anaphylactic Allergy

• Cefazolin: 2 g IV initial dose, then 1 g IV every 8 hours 1

For Severe Penicillin Allergy

• Clindamycin: 900 mg IV every 8 hours or 300-450 mg orally three times daily (only if susceptibility testing confirms sensitivity) 1
• Vancomycin: 1 g IV every 12 hours (for clindamycin-resistant strains) 1
• Nitrofurantoin: 100 mg orally every 6 hours (for uncomplicated lower UTIs only) 2, 1

Special Considerations

Pregnant Women

• Any amount of GBS in urine during pregnancy indicates heavy colonization 1
• Requires both immediate treatment of the current infection AND intrapartum prophylaxis during labor 1
• Follow-up urine culture after completion of treatment to confirm eradication 1
• Screening at 35-37 weeks gestation is still recommended regardless of previous GBS UTI treatment 1

Antibiotics to Avoid

• Trimethoprim-sulfamethoxazole: Not recommended due to frequent GBS resistance 1
• Erythromycin: Not recommended due to increasing resistance 1, 3
• Tetracyclines: Contraindicated in pregnancy and children <8 years 1
• Fluoroquinolones: Should be avoided when alternatives exist due to FDA warnings about side effects 1

Antibiotic Resistance Patterns

• All GBS isolates generally remain susceptible to penicillin, ampicillin, cefazolin, and vancomycin 1, 3
• Resistance rates to alternative agents:
  • Erythromycin: 21% resistance 3
  • Clindamycin: 4% resistance 3
  • Tetracycline: 81.6% resistance 4
  • Co-trimoxazole: 68.9% resistance 4

Treatment Algorithm

1. Confirm diagnosis: Positive urine culture with ≥50,000 CFUs/mL of GBS with symptoms of UTI 2
2. Assess patient factors:
   • Pregnancy status
   • Penicillin allergy status
   • Severity of infection (uncomplicated vs. complicated/pyelonephritis)
3. Select appropriate antibiotic:
   • Non-pregnant, no penicillin allergy: Penicillin G, ampicillin, or amoxicillin
   • Non-pregnant, non-anaphylactic penicillin allergy: Cefazolin
   • Non-pregnant, severe penicillin allergy: Clindamycin (if susceptible) or vancomycin
   • Pregnant: Penicillin G or ampicillin (plus intrapartum prophylaxis)
4. Determine treatment duration based on infection complexity
5. Follow-up: Confirm eradication with repeat urine culture in pregnant women

Clinical Pitfalls to Avoid

• Failing to obtain susceptibility testing when using alternatives to penicillin/ampicillin
• Using trimethoprim-sulfamethoxazole empirically for GBS UTIs
• Not providing intrapartum prophylaxis for pregnant women with history of GBS UTI
• Failing to differentiate between GBS colonization and true infection
• Not completing the full treatment course even if symptoms resolve quickly