What is the best antibiotic treatment for a urine culture growing Streptococcus agalactiae (Group B Streptococcus)?

Treatment of Streptococcus agalactiae (Group B Streptococcus) Urinary Tract Infection

Critical First Question: Is the Patient Pregnant?

The treatment approach for GBS bacteriuria is fundamentally different between pregnant and non-pregnant patients, and this distinction must guide all clinical decisions. 1

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For Pregnant Women

Immediate Treatment of the UTI

• Penicillin G is the preferred first-line agent due to its narrow spectrum of activity and universal GBS susceptibility, with oral dosing of 500 mg every 6-8 hours for 7-10 days for outpatient treatment. 1, 2

• Ampicillin is an acceptable alternative at 500 mg orally every 8 hours for 7-10 days. 1, 2

• For severe infections requiring hospitalization, use penicillin G 5 million units IV initially, then 2.5 million units IV every 4 hours. 2

Mandatory Intrapartum Prophylaxis

All pregnant women with any concentration of GBS in urine at any point during pregnancy must receive IV antibiotic prophylaxis during labor, regardless of whether the UTI was treated earlier. 1, 2 This is because:

• GBS bacteriuria indicates heavy genital tract colonization and significantly increases the risk of early-onset neonatal disease. 1, 2

• Treating the UTI does not eliminate GBS colonization from the genitourinary tract—recolonization after oral antibiotics is typical. 1

• Intrapartum prophylaxis administered ≥4 hours before delivery is 78% effective in preventing early-onset neonatal GBS disease. 1, 2

Intrapartum Prophylaxis Regimens

For women without penicillin allergy:

• Penicillin G 5 million units IV initially, then 2.5-3.0 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 women with low-risk penicillin allergy (no history of anaphylaxis, angioedema, respiratory distress, or urticaria):

• Cefazolin 2 g IV initially, then 1 g IV every 8 hours until delivery. 1, 2

For women with high-risk penicillin allergy (history of anaphylaxis, angioedema, respiratory distress, or urticaria):

• Obtain clindamycin and erythromycin susceptibility testing immediately. 1, 2

• If susceptible to both: Clindamycin 900 mg IV every 8 hours until delivery. 1, 2

• If resistant to either or susceptibility unknown: Vancomycin 1 g IV every 12 hours until delivery. 1, 2

• Perform D-zone testing on isolates that are erythromycin-resistant but clindamycin-susceptible to detect inducible clindamycin resistance. 1

Critical Pitfalls in Pregnancy

• Never assume that treating the UTI eliminates the need for intrapartum prophylaxis—this is a common and dangerous error. 1

• Approximately 13-25% of GBS isolates are resistant to clindamycin, making susceptibility testing mandatory before use. 1, 2, 3

• Erythromycin resistance ranges from 4.7-31%, further emphasizing the need for susceptibility testing in penicillin-allergic patients. 4, 3, 5

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For Non-Pregnant Patients

When to Treat

Treat GBS bacteriuria in non-pregnant patients only if the patient is symptomatic (dysuria, frequency, urgency, suprapubic pain, flank tenderness) or has underlying urinary tract abnormalities. 1, 6

When NOT to Treat

Do not treat asymptomatic bacteriuria in non-pregnant adults, even with GBS present in urine. 6 This includes:

• Patients with diabetes mellitus. 1
• Elderly or institutionalized individuals. 1
• Patients with indwelling urinary catheters. 1
• Patients with neurogenic bladder on intermittent catheterization. 1
• Patients with a history of recurrent UTIs. 1

Treating asymptomatic bacteriuria leads to unnecessary antibiotic exposure, increased resistance, and adverse drug effects without clinical benefit. 1, 6

Treatment Regimens for Symptomatic Non-Pregnant Patients

First-line options:

• Penicillin G 500 mg orally every 6-8 hours for 7-10 days (preferred due to narrow spectrum). 6

• Ampicillin 500 mg orally every 8 hours for 7-10 days (acceptable alternative). 6, 7

For penicillin-allergic patients:

• Clindamycin 300-450 mg orally every 8 hours, only after susceptibility testing confirms susceptibility. 6

For complicated infections or when prostatitis cannot be excluded in men:

• Extend treatment to 14 days. 6

• Consider initial IV therapy with ampicillin 2 g IV every 4-6 hours, then transition to oral therapy once clinically stable. 6

Antibiotic Susceptibility Data

• All GBS isolates remain universally susceptible to penicillin, ampicillin, and vancomycin. 4, 3, 5

• Nitrofurantoin shows excellent activity against GBS and may be considered for uncomplicated cystitis in non-pregnant patients. 4

• Never use fluoroquinolones, sulfonamides, or tetracyclines for GBS infections—they lack proven efficacy. 2

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Key Clinical Distinctions

The CDC guidelines mandating treatment of all GBS bacteriuria apply specifically to pregnant women to prevent neonatal disease and should not be applied to non-pregnant patients. 6 In non-pregnant adults, the decision to treat is based solely on the presence of urinary symptoms or underlying urinary tract abnormalities. 1, 6