Definition of Asymptomatic Bacteriuria
Asymptomatic bacteriuria is the isolation of a specified quantitative count of bacteria in an appropriately collected urine specimen from a person without any symptoms or signs referable to urinary infection. 1
Diagnostic Criteria by Patient Population
The diagnosis requires quantitative urine culture—urinalysis alone is insufficient for definitive diagnosis. 2 The specific bacterial thresholds vary based on sex and collection method:
Women (Non-Catheterized)
- Two consecutive voided urine specimens are required 1, 3, 2
- Both specimens must show ≥10^5 CFU/mL of the same bacterial strain 1, 3, 4
- The two-specimen requirement exists because transient bacteriuria is common in healthy women, and a single positive specimen is confirmed on repeat testing only 80% of the time 1, 2
- When two successive specimens show consistent results, a third consecutive specimen confirms bacteriuria in 95% of cases 1
Men (Non-Catheterized)
- A single clean-catch voided urine specimen is sufficient 1, 3, 2
- Must show ≥10^5 CFU/mL of one bacterial species 1, 3, 4
- This single-specimen criterion has 98% reproducibility when repeated within one week 1, 2
Catheterized Patients (Both Sexes)
- A single catheterized urine specimen is sufficient 1, 3, 2
- Must show ≥10^2 CFU/mL of one bacterial species 1, 3, 4
- The lower threshold (10^2 vs 10^5) reflects the reduced contamination risk with catheterized specimens 2
Essential Collection Requirements
The urine specimen must be collected in a manner that minimizes contamination and transported to the laboratory promptly to limit bacterial growth. 1, 2 For voided specimens, use clean-catch midstream technique. 2
Critical Distinction: Pyuria Is NOT an Indication for Treatment
Pyuria (increased polymorphonuclear leukocytes in urine) accompanying asymptomatic bacteriuria is NOT an indication for antimicrobial treatment. 1, 3, 2, 4 This is a common pitfall—the presence of white blood cells in urine does not convert asymptomatic bacteriuria into a condition requiring treatment. 2
Prevalence Across Populations
Asymptomatic bacteriuria prevalence varies widely: 3
- Healthy premenopausal women: 1.0-5.0% 3
- Pregnant women: 1.9-9.5% 3
- Diabetic women: 9.0-27% 3
- Community-dwelling elderly women: 10.8-16% 3
- Long-term care facility residents: 25-50% (women), 15-40% (men) 3
- Patients with long-term indwelling catheters: 100% 3
Common Diagnostic Pitfalls to Avoid
Do not diagnose or treat based on dipstick urinalysis or pyuria alone—urine culture with quantitative counts is mandatory. 2 Do not confuse nonspecific symptoms (delirium, falls) in elderly patients with symptomatic UTI, as these populations have high baseline bacteriuria prevalence. 3 Asymptomatic bacteriuria should generally not be treated except in pregnant women and patients undergoing urologic procedures with mucosal bleeding. 3, 4