How should I treat a urinary tract infection caused by Group B Streptococcus (Streptococcus agalactiae) in an adult, including recommendations for pregnant patients and those with penicillin allergy?

Treatment of Group B Streptococcus Urinary Tract Infection

For non-pregnant adults with symptomatic GBS UTI, treat with ampicillin or penicillin; for pregnant women, treat the acute infection immediately and provide mandatory intravenous intrapartum antibiotic prophylaxis during labor regardless of prior treatment. 1

Non-Pregnant Adults

When to Treat

• Treat GBS bacteriuria only when the patient has classic urinary symptoms (dysuria, frequency, urgency, suprapubic pain, flank tenderness) or systemic signs of infection (fever, rigors, hemodynamic instability). 1
• Do not treat asymptomatic GBS bacteriuria in non-pregnant adults—this leads to unnecessary antibiotic exposure, promotes resistance, and provides no clinical benefit. 1, 2
• The single exception is patients scheduled for endoscopic urologic procedures involving mucosal trauma, who should receive pre-procedure treatment. 1

First-Line Treatment (No Penicillin Allergy)

• Ampicillin 2 g IV initially, then 1 g IV every 6 hours for 7–14 days based on infection severity. 3
• Penicillin remains the gold standard because all GBS isolates worldwide demonstrate 100% susceptibility to penicillin and ampicillin. 2, 4, 5, 6

Penicillin-Allergic Patients

• For low-risk allergy (no history of anaphylaxis, angioedema, respiratory distress, or urticaria): use cefazolin 2 g IV initially, then 1 g IV every 8 hours. 1, 2
• For high-risk allergy: immediately order clindamycin and erythromycin susceptibility testing, as clindamycin resistance ranges from 13–25% among GBS isolates. 2, 3, 5, 6
  • If susceptible to both agents: clindamycin 900 mg IV every 8 hours. 1, 2
  • If resistant or susceptibility unknown: vancomycin 1 g IV every 12 hours. 1, 2
  • Perform D-zone testing on isolates that are erythromycin-resistant but clindamycin-susceptible to detect inducible clindamycin resistance. 2, 3
• Alternative options for confirmed penicillin and cephalosporin allergy include aztreonam or carbapenems (e.g., ertapenem), which exhibit negligible cross-reactivity. 2

Clinical Context

• GBS accounts for approximately 2% of positive urine cultures in non-pregnant adults, with 85% occurring in women. 7
• The presence of GBS bacteriuria signals a need to screen for underlying urinary tract abnormalities, as 60% of patients have structural abnormalities and 27% have chronic renal failure. 7

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Pregnant Women

Critical Management Principle

Any concentration of GBS in urine during pregnancy—even as low as 10,000 CFU/mL—mandates immediate treatment of the acute UTI plus mandatory intravenous intrapartum antibiotic prophylaxis during labor, regardless of whether the UTI was treated earlier in pregnancy. 1, 2

Why Both Treatments Are Required

• GBS bacteriuria at any concentration indicates heavy genital tract colonization and significantly increases the risk of early-onset neonatal GBS disease. 1
• Treating the UTI with oral or IV antibiotics during pregnancy does not eliminate GBS colonization from the genitourinary tract—recolonization after antibiotics is typical. 1
• Intrapartum prophylaxis administered ≥4 hours before delivery reduces early-onset neonatal GBS disease by 78%. 1, 3

Treatment of Acute UTI

• Treat the symptomatic UTI immediately according to standard pregnancy UTI protocols using pregnancy-safe antibiotics guided by susceptibility testing. 1
• The specific antibiotic choice for acute UTI treatment should be based on local resistance patterns and pregnancy safety profiles.

Intrapartum Prophylaxis Regimens

First-Line (No Penicillin Allergy)

• Penicillin G 5 million units IV initially, then 2.5–3.0 million units IV every 4 hours until delivery (preferred agent due to narrow spectrum and universal GBS susceptibility). 1, 2, 3
• Ampicillin 2 g IV initially, then 1 g IV every 4 hours until delivery (acceptable alternative with broader spectrum). 1, 3

Low-Risk Penicillin Allergy

• Cefazolin 2 g IV initially, then 1 g IV every 8 hours until delivery (preferred alternative for patients without history of anaphylaxis, angioedema, respiratory distress, or urticaria). 1, 2, 3
• Approximately 10% of patients with penicillin allergy exhibit cross-reactivity to cephalosporins, but cefazolin remains safe for low-risk allergic patients. 2

High-Risk Penicillin Allergy

• Immediately obtain clindamycin and erythromycin susceptibility testing on the GBS isolate. 1, 2, 3
• If susceptible to both: clindamycin 900 mg IV every 8 hours until delivery. 1, 2, 3
• If resistant to either or susceptibility unknown: vancomycin 1 g IV every 12 hours until delivery. 1, 2, 3
• Perform D-zone testing on isolates that are erythromycin-resistant but clindamycin-susceptible to detect inducible clindamycin resistance. 1, 2, 3

Special Pregnancy Scenarios

Preterm Labor (<37 weeks)

• Administer GBS prophylaxis immediately upon hospital admission if the patient has documented GBS bacteriuria or unknown GBS status. 1, 3
• Discontinue prophylaxis if the patient is not in true labor. 1, 3

Preterm Premature Rupture of Membranes (PPROM)

• Ampicillin 2 g IV once, followed by 1 g IV every 6 hours for at least 48 hours provides both latency support and adequate GBS prophylaxis. 1, 3

First Trimester GBS UTI

• Treat the acute UTI immediately, but document the finding clearly because intrapartum prophylaxis will still be required during labor months later, regardless of successful UTI treatment. 1
• Women with documented GBS bacteriuria at any point in pregnancy should not be re-screened with vaginal-rectal cultures at 35–37 weeks—they are presumed to be GBS colonized and automatically qualify for intrapartum prophylaxis. 1

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Critical Pitfalls to Avoid

• Never treat asymptomatic GBS vaginal colonization with oral or IV antibiotics before labor—this is completely ineffective at eliminating carriage, does not prevent neonatal disease, and promotes antibiotic resistance. 1, 2
• Never assume that treating a GBS UTI during pregnancy eliminates the need for intrapartum prophylaxis—this is a dangerous error that increases neonatal risk. 1
• Never delay intrapartum prophylaxis while awaiting culture results when risk factors are present (labor <37 weeks, membrane rupture ≥18 hours, intrapartum fever ≥38°C). 3
• Never prescribe clindamycin for high-risk penicillin-allergic patients without confirmed susceptibility testing, as resistance rates reach 13–25%. 2, 3, 5, 6
• Never treat non-pregnant adults with asymptomatic GBS bacteriuria and only nonspecific symptoms (malaise, fatigue)—this causes harm without benefit. 1

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Laboratory Considerations

• Laboratories should report GBS in urine when present at concentrations ≥10,000 CFU/mL (≥10⁴ CFU/mL). 1, 2
• Inform laboratories when urine specimens are from pregnant women so they report GBS at the appropriate threshold. 1
• Susceptibility testing must include clindamycin and erythromycin for all penicillin-allergic pregnant patients at high risk for anaphylaxis. 1, 2