What is the recommended treatment for a urinary tract infection caused by Group B Streptococcus (GBS) with a colony count of 50,000-100,000 CFU/mL?

Treatment of Urinary Tract Infection Caused by Group B Streptococcus

Penicillin or ampicillin should be used as first-line treatment for Group B Streptococcus urinary tract infection with a colony count of 50,000-100,000 CFU/mL.

Antibiotic Selection Algorithm

First-line options:

• Penicillin G: Preferred due to its narrow spectrum and effectiveness against GBS
• Ampicillin: Effective alternative to penicillin

For penicillin-allergic patients:

1. Low risk of anaphylaxis:

   • Cefazolin: First alternative for patients with non-severe penicillin allergy

2. High risk of anaphylaxis:

   • Clindamycin: Only if susceptibility testing confirms sensitivity
   • Vancomycin: For clindamycin-resistant isolates

Treatment Duration and Dosing

• Uncomplicated UTI: 7-10 days of treatment
• Complicated UTI: 10-14 days of treatment
• Continue treatment for at least 48-72 hours after symptom resolution 1

Specific Dosing Recommendations:

• Ampicillin: 500 mg every 8 hours (mild/moderate) or 875 mg every 12 hours (severe) 1
• Penicillin G: IV 5 million units initially, then 2.5 million units every 4 hours

Important Clinical Considerations

Antibiotic Resistance Patterns

• Beta-hemolytic streptococci, including GBS, remain highly susceptible to penicillin and other beta-lactams 2
• Erythromycin and clindamycin are not recommended for treatment of urinary tract infections, as noted in the laboratory report
• Rising resistance to clindamycin (28%) and erythromycin (30%) has been documented 3, with some studies showing penicillin resistance emerging in certain regions (18.3%) 4

Special Populations

• Pregnant women: GBS bacteriuria during pregnancy requires treatment and indicates need for intrapartum antibiotic prophylaxis during delivery 2
• Diabetic patients: May have increased susceptibility to GBS UTI and potentially altered immune response 5

Follow-up Recommendations

• Obtain follow-up urine culture after completion of treatment to confirm eradication, especially in high-risk patients
• Screen for underlying urinary tract abnormalities, as GBS UTI is associated with urinary tract abnormalities in 60% of cases 6

Pitfalls to Avoid

1. Do not use erythromycin for GBS UTI due to increasing resistance and poor urinary concentrations
2. Do not use clindamycin empirically without susceptibility testing
3. Do not discontinue treatment prematurely before completing the full course
4. Do not neglect follow-up cultures in high-risk patients or those with recurrent symptoms

Remember that while GBS accounts for only about 2% of positive urine cultures in non-pregnant adults 6, proper identification and targeted treatment are essential to prevent complications and treatment failures.