How should group B Streptococcus (GBS) bacteriuria be treated in adults, including first‑line antibiotics, duration, alternatives for penicillin allergy, and follow‑up recommendations?

Treatment of Group B Streptococcus Bacteriuria in Adults

First-Line Antibiotic Therapy

For non-pregnant adults with GBS bacteriuria and no penicillin allergy, treat with intravenous penicillin G or oral amoxicillin for 7–10 days, as GBS remains universally susceptible to beta-lactam antibiotics worldwide. 1, 2

• Penicillin G remains the drug of choice because all GBS isolates worldwide retain 100% susceptibility to penicillin, with no confirmed resistance documented to date. 1, 2
• Oral amoxicillin is an acceptable alternative for outpatient management when intravenous therapy is not feasible. 1
• Treatment duration of 7–10 days is standard for uncomplicated urinary tract infections caused by GBS, though specific duration data for non-pregnant adults are limited. (General medicine knowledge applied to GBS UTI context)

Management in Pregnancy (Special Population)

Pregnant women with GBS bacteriuria at any colony count should receive intrapartum antibiotic prophylaxis (IAP) at the time of labor or rupture of membranes, not antepartum treatment, to prevent early-onset neonatal GBS disease. 3, 4

• Women with documented GBS bacteriuria (regardless of CFU/mL) in the current pregnancy should receive intravenous penicillin G during labor as IAP. 3, 4
• Do not re-screen these women with third-trimester vaginal-rectal cultures, as they are presumed to remain GBS-colonized throughout pregnancy. 3
• Asymptomatic GBS bacteriuria with colony counts <100,000 CFU/mL should not be treated with antibiotics during pregnancy for prevention of pyelonephritis, chorioamnionitis, or preterm birth. 3
• Symptomatic bacteriuria or colony counts ≥100,000 CFU/mL should be treated at the time of diagnosis with appropriate antibiotics. 3

Treatment Algorithm for Penicillin Allergy

Non-Severe (Delayed) Penicillin Allergy

For patients with non-severe penicillin reactions (mild rash, delayed symptoms), prescribe cefazolin 1–2 g IV every 8 hours, as cross-reactivity risk is only approximately 0.1%. 1, 5

• Cefazolin is the recommended first-line alternative because GBS isolates remain highly susceptible to first-generation cephalosporins. 1
• This applies to patients without a history of anaphylaxis, angioedema, respiratory distress, or urticaria following penicillin exposure. 1

Severe (Immediate/Anaphylactic) Penicillin Allergy

For patients with severe penicillin allergy (anaphylaxis, angioedema, respiratory distress, or urticaria), vancomycin 1 g IV every 12 hours is the recommended first-line treatment when susceptibility testing is unavailable or pending. 1

• Obtain antimicrobial susceptibility testing for clindamycin and erythromycin on all GBS isolates from penicillin-allergic patients. 1, 5
• If susceptibility results show the isolate is clindamycin-susceptible, switch to clindamycin 900 mg IV every 8 hours (or 600 mg IV every 8 hours for less severe infections). 1
• If the isolate is clindamycin-resistant or erythromycin-resistant, continue vancomycin 1 g IV every 12 hours. 1
• Perform D-zone testing on isolates that are erythromycin-resistant but clindamycin-susceptible to detect inducible clindamycin resistance, as resistance to erythromycin frequently (but not always) predicts clindamycin resistance. 1

Antibiotic Resistance Patterns

• Penicillin resistance: Zero documented cases worldwide; all GBS isolates remain 100% susceptible to penicillin and ampicillin. 1, 2
• Clindamycin resistance: Ranges from 3–15% among invasive GBS isolates in the United States, with some studies reporting up to 13–25% resistance. 1, 2, 6
• Erythromycin resistance: Remains high at approximately 25% in recent studies, with increasing resistance rates noted in several countries. 2, 6
• Vancomycin resistance: Only two documented cases of vancomycin-resistant GBS have been reported worldwide; vancomycin remains largely effective as a last-resort antibiotic. 2, 6

Critical Pitfalls to Avoid

• Do not use cefazolin in patients with severe (immediate/anaphylactic) penicillin allergy due to approximately 10% cross-reactivity risk with cephalosporins. 1, 5
• Do not rely on erythromycin for GBS infections, as it is no longer recommended due to increasing resistance rates (≈25%) and is not an effective alternative. 1, 2, 6
• Do not assume clindamycin susceptibility without testing; always obtain susceptibility results before using clindamycin in penicillin-allergic patients, as 13–25% of GBS isolates may be resistant. 1, 2, 6
• Do not treat asymptomatic GBS bacteriuria in non-pregnant adults without considering clinical context; treatment is primarily indicated for symptomatic infections or in pregnancy. 3

Follow-Up Recommendations

• No routine follow-up urine cultures are recommended for asymptomatic patients who have completed appropriate antibiotic therapy. (Standard UTI management principle)
• Pregnant women with documented GBS bacteriuria do not require repeat screening or cultures, as they should automatically receive IAP during labor. 3
• Consider infectious disease consultation for complicated cases, treatment failures, or when limited antibiotic options are available due to allergies and resistance patterns. 1