What is the recommended treatment for a urinary tract infection (UTI) caused by Streptococcus agalactiae (Group B streptococcus) in a patient, considering potential underlying health conditions and antibiotic allergy?

Treatment of Streptococcus agalactiae (Group B Streptococcus) Urinary Tract Infection

For non-pregnant patients with symptomatic GBS UTI, treat with ampicillin 500 mg orally every 8 hours for 7-10 days, or penicillin G 500 mg orally every 6-8 hours for 7-10 days, as these agents demonstrate universal susceptibility and narrow-spectrum activity. 1, 2

Critical First Step: Determine Pregnancy Status

The management of GBS bacteriuria is fundamentally different between pregnant and non-pregnant patients. 2

• If pregnant: Any concentration of GBS in urine requires immediate treatment of the acute UTI PLUS mandatory intravenous antibiotic prophylaxis during labor, regardless of whether the UTI was treated earlier in pregnancy 1, 2
• If non-pregnant and asymptomatic: Do NOT treat, as this represents asymptomatic bacteriuria that should not be treated 3, 2
• If non-pregnant and symptomatic: Treat according to standard UTI protocols outlined below 2

Treatment Algorithm for Non-Pregnant Patients

For Uncomplicated Symptomatic UTI (No Penicillin Allergy)

First-line options:

• Ampicillin 500 mg orally every 8 hours for 7-10 days 2
• Penicillin G 500 mg orally every 6-8 hours for 7-10 days 1, 2
• Amoxicillin (acceptable alternative based on GBS susceptibility patterns) 4

Rationale: GBS demonstrates 96-100% susceptibility to ampicillin and penicillin across multiple studies, with universal susceptibility reported in recent data 5, 6

For Complicated UTI or Systemic Symptoms

Initial therapy:

• Ampicillin 2 g IV every 4-6 hours, then transition to oral therapy once clinically stable 2
• For severe presentations: Ampicillin plus an aminoglycoside combination 3, 2

Duration: Extend to 14 days for complicated infections or when prostatitis cannot be excluded in men 3, 2

For Penicillin-Allergic Patients

Non-high-risk allergy (no history of anaphylaxis, angioedema, or urticaria):

• Cefazolin 2 g IV initially, then 1 g IV every 8 hours 1
• First-generation cephalosporins are preferred over later generations 1

High-risk allergy (history of immediate hypersensitivity reactions):

• Clindamycin 300-450 mg orally every 8 hours (ONLY if susceptibility testing confirms susceptibility) 2
• Critical caveat: Clindamycin resistance ranges from 3-77% in different populations, making susceptibility testing mandatory before use 1, 5, 6
• If resistant or susceptibility unknown: Vancomycin 1 g IV every 12 hours 1

Special Considerations for Pregnant Patients

Immediate Management

All pregnant patients with GBS bacteriuria at any concentration require:

1. Treatment of the acute UTI at diagnosis 1
2. Mandatory intrapartum IV antibiotic prophylaxis during labor 1, 2

Critical pitfall: Treating the UTI during pregnancy does NOT eliminate GBS colonization from the genitourinary tract—recolonization after oral antibiotics is typical, which is why intrapartum IV prophylaxis remains mandatory even if bacteriuria was treated earlier 1

Intrapartum Prophylaxis Regimens

Preferred regimen (no penicillin allergy):

• Penicillin G 5 million units IV initially, then 2.5-3.0 million units IV every 4 hours until delivery 1
• Alternative: Ampicillin 2 g IV initially, then 1 g IV every 4 hours until delivery 1

For penicillin allergy (not high-risk):

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

For high-risk penicillin allergy:

• Clindamycin 900 mg IV every 8 hours until delivery (if susceptible) 1
• Vancomycin 1 g IV every 12 hours until delivery (if resistant or unknown susceptibility) 1

Timing: Intrapartum prophylaxis must be administered ≥4 hours before delivery for maximum effectiveness, resulting in 78% reduction in early-onset neonatal GBS disease 1

Antibiotic Susceptibility Patterns

High susceptibility (>95%):

• Penicillin/Ampicillin: 96-100% 5, 6
• Vancomycin: 95-100% 5, 6
• Cephalothin: 100% 5
• Norfloxacin: 96.9% 5
• Nitrofurantoin: 95.5% 5

High resistance (avoid empirically):

• Tetracycline: 81.6-88.46% resistance 5, 6
• Co-trimoxazole: 68.9% resistance 5
• Clindamycin: 77.34% resistance in some populations 6

Common Pitfalls to Avoid

1. Do NOT treat asymptomatic bacteriuria in non-pregnant patients: This leads to unnecessary antibiotic exposure, resistance development, and potential adverse effects without clinical benefit 3, 2

2. Do NOT assume treating UTI in pregnancy eliminates need for intrapartum prophylaxis: This is a common and dangerous error that increases risk of early-onset neonatal GBS disease 1

3. Do NOT use clindamycin without susceptibility testing: Resistance rates vary widely (3-77%), making empiric use inappropriate 1, 5, 6

4. Do NOT use fluoroquinolones empirically: Only use ciprofloxacin if local resistance rate is <10% and patient has not used fluoroquinolones in the last 6 months 3

5. Do NOT treat GBS vaginal colonization outside of labor: Oral or IV antibiotics given before labor are completely ineffective at eliminating GBS colonization and should never be used for asymptomatic vaginal colonization 1

Follow-Up and Monitoring

• Follow-up urine culture after treatment completion may be warranted to ensure eradication, especially in patients with recurrent UTIs 2
• For pregnant patients: Document GBS bacteriuria in medical records and communicate to anticipated site of delivery 1
• Consider evaluation for reservoirs of infection (vagina, urethra, gastrointestinal tract) in cases of recurrent infection 4, 7