What is the recommended antibiotic regimen for a urinary tract infection caused by beta‑hemolytic Streptococcus (group B Streptococcus), including options for pregnant patients and those with severe penicillin allergy?

Treatment of Beta-Hemolytic Streptococcus (Group B Streptococcus) Urinary Tract Infection

Penicillin G or ampicillin is the first-line treatment for GBS urinary tract infections, with all GBS isolates worldwide remaining 100% susceptible to penicillin. 1

First-Line Antibiotic Regimens for Non-Allergic Patients

For patients without penicillin allergy, penicillin G 5 million units IV initially, then 2.5-3.0 million units IV every 4 hours is the preferred regimen due to its narrow spectrum and universal GBS susceptibility. 1

• Ampicillin 2g IV initially, then 1g IV every 4 hours is an acceptable alternative, though it has broader spectrum activity. 1
• All GBS isolates remain universally susceptible to beta-lactam antibiotics, with no confirmed resistance to penicillin or ampicillin observed worldwide. 1, 2, 3, 4

Management of Penicillin-Allergic Patients

The approach depends critically on whether the patient is at high risk for anaphylaxis. High-risk allergy is defined as a history of anaphylaxis, angioedema, respiratory distress, or urticaria following penicillin or cephalosporin administration. 5

For Non-High-Risk Penicillin Allergy:

• Cefazolin 2g IV initially, then 1g IV every 8 hours is the preferred alternative. 1
• Approximately 10% of penicillin-allergic patients have cross-reactivity with cephalosporins, but cefazolin remains safe for those without high-risk symptoms. 5

For High-Risk Penicillin Allergy:

Susceptibility testing for clindamycin and erythromycin must be obtained immediately, as clindamycin resistance ranges from 3-15% among GBS isolates. 5, 1, 2, 3

• If susceptible to both clindamycin and erythromycin: Clindamycin 900 mg IV every 8 hours. 1
• If resistant to either antibiotic or susceptibility unknown: Vancomycin 1g IV every 12 hours. 1
• D-zone testing must be performed on isolates that are erythromycin-resistant but clindamycin-susceptible to detect inducible clindamycin resistance. 5, 1

Critical Special Considerations for Pregnant Patients

Any concentration of GBS in urine during pregnancy (≥10⁴ CFU/ml) requires immediate treatment AND mandatory intrapartum IV antibiotic prophylaxis during labor, regardless of whether the UTI was treated earlier in pregnancy. 5, 1, 6

Why Pregnancy Changes Everything:

• GBS bacteriuria during pregnancy indicates heavy genital tract colonization and significantly increases the risk of early-onset neonatal GBS disease. 1, 6
• Treating the UTI during pregnancy does NOT eliminate GBS colonization from the genitourinary tract—recolonization after oral antibiotics is typical. 6
• Intrapartum prophylaxis administered ≥4 hours before delivery is 78% effective in preventing early-onset neonatal GBS disease. 1, 6

Intrapartum Prophylaxis Regimens for Pregnant Patients:

• Penicillin G 5 million units IV initially, then 2.5 million units IV every 4 hours until delivery (preferred). 1, 6
• Ampicillin 2g IV initially, then 1g IV every 4 hours until delivery (acceptable alternative). 1, 6
• For non-high-risk penicillin allergy: Cefazolin 2g IV initially, then 1g IV every 8 hours until delivery. 1, 6
• For high-risk allergy with susceptible isolate: Clindamycin 900 mg IV every 8 hours until delivery. 1, 6
• For high-risk allergy with resistant/unknown susceptibility: Vancomycin 1g IV every 12 hours until delivery. 1, 6

Laboratory Reporting Requirements

Laboratories should report GBS in urine culture specimens when present at concentrations of ≥10⁴ colony-forming units/ml in pure culture or mixed with a second microorganism. 5

• For pregnant patients, laboratories must be informed of pregnancy status to ensure proper reporting thresholds. 1
• Susceptibility testing should be ordered immediately for penicillin-allergic patients at high risk for anaphylaxis. 5

Critical Pitfalls to Avoid

Never use oral antibiotics before labor to treat GBS colonization in pregnant women—this approach is completely ineffective at eliminating carriage and may promote antibiotic resistance. 5, 1

• Do not assume that treating a GBS UTI in pregnancy eliminates the need for intrapartum prophylaxis—this is a dangerous error. 1, 6
• Pregnant women with documented GBS bacteriuria at any point in pregnancy should not be re-screened with vaginal-rectal cultures at 35-37 weeks, as they are presumed to be GBS colonized and automatically qualify for intrapartum prophylaxis. 1
• For preterm labor (<37 weeks) with GBS bacteriuria, GBS prophylaxis should be administered immediately at hospital admission. 1

Non-Pregnant Patient Management

For non-pregnant patients with asymptomatic GBS bacteriuria at low colony counts (10,000-49,000 CFU/mL), treatment is NOT recommended unless the patient is symptomatic or has underlying urinary tract abnormalities. 1

• Treating asymptomatic bacteriuria in non-pregnant populations leads to unnecessary antibiotic exposure, resistance development, and potential adverse effects without clinical benefit. 1