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

Treatment of Group B Streptococcal Urinary Tract Infection

Treat symptomatic or asymptomatic GBS UTI in pregnancy with standard antibiotics according to colony count, and ensure all pregnant women with documented GBS bacteriuria receive intrapartum antibiotic prophylaxis regardless of whether they were treated earlier in pregnancy. 1, 2

Treatment Approach Based on Pregnancy Status

For Pregnant Women

Acute UTI Treatment:

• Women with GBS bacteriuria ≥100,000 CFU/mL should receive standard antibiotic treatment for UTI during pregnancy 3
• Penicillin G (5 million units IV initially, then 2.5 million units IV every 4 hours) is the preferred agent for inpatient treatment due to narrow spectrum activity 2
• Ampicillin (2 g IV initial dose, then 1 g IV every 4 hours) is an acceptable alternative 1, 2
• For oral outpatient treatment, ampicillin 500 mg four times daily is appropriate for genitourinary infections 4
• Complete the full prescribed antibiotic course to ensure eradication and prevent recurrence 2

Critical Point - Intrapartum Prophylaxis:

• All women with documented GBS bacteriuria at ANY colony count during pregnancy must receive intrapartum antibiotic prophylaxis during labor, regardless of whether they were treated earlier 2, 3
• This is mandatory because GBS bacteriuria indicates heavy colonization and significantly increases risk of early-onset neonatal GBS disease 2
• Do NOT re-screen these women with vaginal/rectal cultures at 35-37 weeks—they are presumed colonized 1, 3

Intrapartum Prophylaxis Regimen:

• Penicillin G: 5 million units IV initially, then 2.5-3 million units IV every 4 hours until delivery (preferred) 1, 2
• Ampicillin: 2 g IV initially, then 1 g IV every 4 hours until delivery (acceptable alternative) 1, 2

For Penicillin-Allergic Pregnant Women

Low Risk for Anaphylaxis:

• Cefazolin 2 g IV initially, then 1 g IV every 8 hours is the preferred alternative 1, 2

High Risk for Anaphylaxis:

• Clindamycin 900 mg IV every 8 hours IF the isolate is confirmed susceptible 1, 2
• Approximately 20% of GBS isolates are resistant to clindamycin, making susceptibility testing mandatory 5, 6
• Vancomycin 1 g IV every 12 hours if susceptibility unknown or isolate is clindamycin-resistant 2
• Erythromycin is NOT recommended due to increasing GBS resistance to macrolides 1

For Non-Pregnant Women and Men

First-Line Treatment:

• Penicillin or ampicillin remain the antibiotics of choice with universal susceptibility 6, 7
• Oral ampicillin 500 mg four times daily for genitourinary infections 4
• Treatment duration should be at least 48-72 hours after symptoms resolve 4

Penicillin-Allergic Patients:

• Cefazolin or cephalexin for patients not at high risk for anaphylaxis 5
• Clindamycin (if susceptible) or vancomycin for severe penicillin allergy 5
• Always perform susceptibility testing before using clindamycin given 77% resistance rates in some populations 6

Important Clinical Pitfalls

Do NOT treat asymptomatic GBS bacteriuria <100,000 CFU/mL in pregnancy outside of labor:

• Prenatal antibiotic treatment does not eliminate carriage or prevent neonatal disease 1, 3
• Such treatment is ineffective and may promote antibiotic resistance 1
• However, these women STILL require intrapartum prophylaxis during labor 3

Avoid underdosing or premature discontinuation:

• This leads to treatment failure and recurrence 2, 5
• Stubborn infections may require several weeks of treatment 4

Susceptibility Testing Requirements:

• Mandatory for penicillin-allergic patients at high risk for anaphylaxis 2, 5
• Test for inducible clindamycin resistance (D-test) when isolates are clindamycin-susceptible but erythromycin-resistant 2, 5
• Recent data shows high resistance to clindamycin (77%) and tetracycline (88%), but universal susceptibility to penicillin, ampicillin, and vancomycin 6

Special Monitoring Considerations

Laboratory Reporting:

• GBS detected at ≥10⁴ CFU/mL should be reported as it indicates heavy colonization 2
• Results should be communicated to both the anticipated delivery site and ordering provider 1

Follow-up:

• No repeat screening cultures needed in pregnancy once GBS bacteriuria is documented 1, 3
• For non-pregnant patients, consider follow-up cultures if symptoms persist or in chronic infections 4, 7