Do we treat asymptomatic bacteriuria with a colony count of 50,000 CFU/mL (colony-forming units per milliliter)?

Management of Asymptomatic Bacteriuria with Colony Count of 50,000 CFU/mL

Asymptomatic bacteriuria with a colony count of 50,000 CFU/mL should NOT be treated with antibiotics in most patient populations. 1

Definition and Diagnosis

• Asymptomatic bacteriuria (ASB) is defined as the presence of bacteria in the urine at specified quantitative counts (≥10^5 CFU/mL or ≥10^8 CFU/L) without signs or symptoms attributable to urinary tract infection 1
• For women, two consecutive voided specimens with isolation of the same bacterial strain in quantitative counts of ≥10^5 CFU/mL are required for diagnosis 1
• For men, a single voided specimen with one bacterial species isolated in a quantitative count of ≥10^5 CFU/mL is sufficient 1
• A colony count of 50,000 CFU/mL (5×10^4) is below the traditional diagnostic threshold but may be significant in certain clinical contexts

Evidence-Based Recommendations by Population

General Population

• Do not screen for or treat ASB in most individuals 1
• Treatment of ASB does not reduce morbidity or mortality in most populations 2
• Unnecessary antibiotics increase risk of:
  • Antimicrobial resistance
  • Clostridioides difficile infection
  • Disruption of normal microbiome 2

Specific Populations Where Treatment IS Recommended

1. Pregnant women

   • Screen and treat ASB in the first trimester 3
   • Treatment reduces risk of pyelonephritis and adverse pregnancy outcomes

2. Patients undergoing invasive urologic procedures

   • Screen and treat prior to procedures where mucosal bleeding is anticipated 1, 3

Specific Populations Where Treatment is NOT Recommended

• Infants and children 1
• Premenopausal, non-pregnant women 1
• Postmenopausal women 1
• Elderly persons in the community or long-term care facilities 1, 3
• Patients with diabetes 1, 3
• Patients with spinal cord injuries 1, 3
• Patients with indwelling or intermittent catheters 1, 3
• Solid organ transplant recipients (except in certain circumstances) 1

Clinical Considerations

• Pyuria (presence of white blood cells in urine) frequently accompanies ASB but is not an indication for treatment 1, 2
• The prevalence of ASB increases with age, reaching 10-16% in elderly women living in the community and 25-50% in those in long-term care facilities 1
• Transient bacteriuria is common in healthy young women 1

Antimicrobial Stewardship

• Non-treatment of ASB is recognized as an important opportunity for antimicrobial stewardship 1, 3
• Multiple studies have shown that treating ASB does not improve outcomes in most populations and may lead to harm 3
• Unnecessary treatment contributes to increasing antibiotic resistance patterns 4, 3

Conclusion

For a patient with asymptomatic bacteriuria and a colony count of 50,000 CFU/mL, the evidence strongly supports withholding antibiotic treatment unless the patient is pregnant or undergoing an invasive urologic procedure. This recommendation aligns with the most recent guidelines from the Infectious Diseases Society of America 1.