From the Guidelines
To determine if a specific urinary bacterium is colonized, the presence of ≥10^5 colony-forming units (CFU)/mL or ≥10^8 CFU/L in the urine without signs or symptoms attributable to urinary tract infection (UTI) is a key indicator, as stated in the 2019 update by the Infectious Diseases Society of America 1. When evaluating colonization, consider the following factors:
- The absence of urinary symptoms like burning, frequency, urgency, or pain despite a positive urine culture
- Laboratory findings showing bacteria in the urine without significant white blood cells
- Quantitatively, bacterial counts between 10,000-100,000 CFU/mL without symptoms may suggest colonization, especially in certain populations like elderly individuals, pregnant women, or catheterized patients
- Repeated cultures showing the same organism without symptoms over time further supports colonization Key populations to consider for colonization include:
- Healthy female populations
- Women or men with abnormalities of the genitourinary tract that impair voiding
- Children, as the current guideline reviews and updates previous recommendations, incorporating new evidence that has become available 1 It's essential to distinguish colonization from infection, as asymptomatic bacteriuria (colonization) generally doesn't require treatment except in specific situations such as pregnancy or before urologic procedures, to avoid unnecessary antibiotics that can lead to resistance and disruption of normal flora 1.
From the Research
Determining Urinary Bacterium Colonization
To determine if a specific urinary bacterium is colonized, the following methods can be used:
- Quantitative urine culture, which is considered the definitive diagnosis of urinary tract infection (UTI) 2
- Presence of specific symptoms and pyuria, which can indicate UTI even with a low number of bacteria in urine 2
- Use of chromogenic culture media, which can directly identify uropathogens and detect polymicrobial cultures 2
- Automatic systems, which can rapidly rule out the presence of UTI, although their clinical utility is controversial 2
Factors to Consider
When determining urinary bacterium colonization, the following factors should be considered:
- The type of bacterium present, as some are more commonly associated with UTIs than others 3, 4, 5
- The patient's symptoms and medical history, as these can affect the interpretation of test results 3, 6
- The antibiotic susceptibility pattern of the bacterium, as this can affect treatment options 4, 5
- The use of rapid diagnostic testing, which can help reduce the use of inaccurate or broad-spectrum empiric antimicrobials 6
Diagnostic Methods
The following diagnostic methods can be used to determine urinary bacterium colonization:
- Urine culture and sensitivity (C&S), which is the gold standard diagnostic for UTIs 6
- Rapid identification and quantification (IDQ) and antimicrobial susceptibility testing (AST), which can provide results within 30 and 150 min, respectively 6
- Microscopy and conventional semi-quantitative culture technique, which can be used to analyze midstream urine samples 5
- Modified Kirby-Bauer disk diffusion method, which can be used to perform antimicrobial susceptibility tests 5