Do we treat a urine culture with 10,000-49,000 colony-forming units (CFU) of Group B Streptococcus (GBS) beta-hemolytic as a urinary tract infection (UTI)?

Management of Group B Streptococcus in Urine Culture with 10,000-49,000 CFU/mL

Group B Streptococcus (GBS) in urine at any concentration during pregnancy should be treated as a urinary tract infection, but in non-pregnant adults, GBS with colony counts of 10,000-49,000 CFU/mL should not be treated unless the patient is symptomatic. 1, 2

Pregnancy Status Considerations

Pregnant Women

• GBS bacteriuria at any concentration during pregnancy is clinically significant 1, 2
• Treatment is required for:
  • Symptomatic infections (treat according to current UTI standards) 1
  • Asymptomatic bacteriuria with GBS (regardless of colony count) 2, 3
• Rationale:
  • GBS bacteriuria is a marker for heavy genital tract colonization 2
  • Associated with increased risk for early-onset neonatal GBS disease 1, 2
  • Women with GBS in urine are at higher risk of delivering infants with early-onset GBS disease 1

Non-Pregnant Adults

• Colony counts <100,000 CFU/mL without symptoms should not be treated 1, 3
• The USPSTF concludes with moderate certainty that the harms of screening and treating asymptomatic bacteriuria in non-pregnant adults outweigh the benefits 1
• Consider treatment only if:
  • Colony count ≥100,000 CFU/mL
  • Patient has symptoms of UTI
  • Patient has risk factors (urinary tract abnormalities, chronic renal failure) 4

Treatment Approach

For Pregnant Women

1. Immediate Treatment:

   • Treat symptomatic UTI according to current standards of care 1
   • Appropriate antibiotics include:
     • Oral amoxicillin-clavulanic acid (first-line) 2
     • Nitrofurantoin (alternative) 2

2. Intrapartum Prophylaxis:

   • All pregnant women with GBS bacteriuria at any point during pregnancy require intrapartum antibiotic prophylaxis (IAP) during labor 1, 2, 3
   • Do not re-screen these women with genital tract or urine cultures in the third trimester 3
   • IAP regimens:
     • Penicillin G: 5 million units IV initial dose, then 2.5-3.0 million units IV every 4 hours until delivery
     • Ampicillin: 2 g IV initial dose, then 1 g IV every 4 hours until delivery
     • For penicillin allergy: Cefazolin or clindamycin (if susceptible) 2

For Non-Pregnant Adults

• If symptomatic or if colony count ≥100,000 CFU/mL:
  • Treat with appropriate antibiotics based on susceptibility testing 4
  • Consider screening for urinary tract abnormalities, as GBS UTI is associated with underlying urologic conditions 4

Important Clinical Considerations

Antibiotic Resistance

• Increasing resistance patterns have been reported:
  • Penicillin resistance: 18.3% in some populations 5
  • Ampicillin resistance: up to 81.6% in some regions 5
  • Clindamycin resistance: 14-26.6% 2, 5
• Always consider local resistance patterns when selecting antibiotics

Common Pitfalls to Avoid

1. Dismissing GBS as a contaminant

   • GBS should not be considered merely a contaminant when isolated in urine cultures 6
   • Laboratory personnel should characterize the organism and perform biochemical testing 2

2. Inappropriate antibiotic use

   • Treating asymptomatic non-pregnant adults with low colony counts contributes to antibiotic resistance 1
   • Treating GBS colonization with oral antibiotics before the intrapartum period does not prevent early-onset GBS disease 2

3. Missing intrapartum prophylaxis

   • Ensure that information about GBS bacteriuria is communicated to all providers involved in a pregnant patient's care 2
   • Document GBS status prominently in the prenatal record

Special Populations

• Patients with urinary tract abnormalities or chronic renal failure have higher risk of GBS UTI 4
• Consider more aggressive treatment approach in these high-risk groups

By following these evidence-based guidelines, clinicians can appropriately manage GBS in urine cultures while minimizing unnecessary antibiotic use and preventing serious complications, particularly in pregnant women.