What is catheter-associated bacteriuria in patients with an indwelling urinary catheter?

What is Catheter-Associated Bacteriuria?

Catheter-associated bacteriuria is the presence of bacteria in the urine (≥10³ CFU/mL) in a patient with an indwelling urinary catheter, occurring at a rate of 3-5% per catheter day, and ultimately develops in all patients if the catheter remains in place long enough due to universal biofilm formation. 1

Key Epidemiologic Features

Acquisition and Timeline

• Bacteriuria develops at a predictable rate of 3-5% per catheter day in catheterized patients 1
• All patients ultimately develop bacteriuria if an indwelling catheter remains in situ due to universal biofilm formation along the catheter surface 1
• Among newly catheterized patients, approximately 14.9% develop bacteriuria at a mean of 6.4 days 1
• Many patients with short-term catheters (in place for <30 days) do not develop bacteriuria because the catheter is removed prior to acquisition 1

Chronic vs. Short-Term Catheterization

• Individuals with chronic indwelling catheters are generally always bacteriuric, usually with a polymicrobial flora 1
• In chronically catheterized patients, 98% of urine specimens contain bacteria at high concentrations and 77% are polymicrobial 2
• The mean interval between new episodes of bacteriuria in chronic catheterization is only 1.8 weeks 2

Critical Distinction: Bacteriuria vs. Infection

Most Bacteriuria is Asymptomatic

• Only 7.7% of patients with catheter-associated bacteriuria report subjective symptoms 1
• The prevalence of symptoms referable to the urinary tract, including fever, does not differ between patients with or without bacteriuria 1
• In one study of 444 episodes of catheter-associated bacteriuria, 58.4% had asymptomatic bacteriuria (ASB) and only 41.6% had symptomatic catheter-associated UTI (CAUTI) 1

Low Risk of Serious Complications

• Bacteremia directly attributable to catheter-associated bacteriuria occurs in only 0.5-0.7% of bacteriuric patients 1
• Short-term catheter-associated bacteriuria does not appear to increase the risk for sepsis or death 1
• After adjustment for confounders, catheter-associated bacteriuria is not associated with increased mortality 1

Biofilm Formation and Antimicrobial Resistance

Universal Biofilm Development

• Biofilm formation on the inner and outer catheter surfaces is a universal phenomenon that occurs once catheters are inserted 3
• These established biofilms inherently protect uropathogens from antimicrobials and the host immune response 3
• The biofilm appears as a white, cloudy substance and represents bacterial colonization with associated mineral precipitation 3

Antimicrobial Treatment Limitations

• Antimicrobials can only temporarily suppress bacteriuria; recurrence with the same or different species, often with organisms of increased antimicrobial resistance, occurs universally 1
• Antimicrobial therapy may delay but cannot prevent the onset of bacteriuria 1
• 60-80% of acute care patients with short-term indwelling catheters receive antimicrobials for other indications, which may delay onset and modify the resistance profile of organisms 1

Clinical Implications and Management

When NOT to Treat

• The Infectious Diseases Society of America provides a strong recommendation against screening for or treating asymptomatic bacteriuria in patients with indwelling catheters 4
• Cloudy or smelly urine alone should not be interpreted as indications of symptomatic infection 5
• In one study, 32% of episodes of catheter-associated asymptomatic bacteriuria were inappropriately treated with antibiotics 6

When to Consider Treatment

• Treatment is only warranted when patients develop systemic symptoms such as fever, rigors, altered mental status, malaise, lethargy, flank pain, costovertebral angle tenderness, acute hematuria, or pelvic discomfort 1, 5
• Specific high-risk situations may warrant treatment: planned urologic procedure with anticipated mucosal bleeding, pregnancy, or high-risk neutropenia 4

Prevention Strategies

• Catheter-associated UTIs are the leading cause of secondary health care-associated bacteremia, with approximately 20% of hospital-acquired bacteremias arising from the urinary tract 1
• The mortality associated with catheter-associated bacteremia is approximately 10% 1
• Catheterization duration is the most important risk factor for catheter-associated UTI development 1
• Removing the catheter as soon as medically feasible can clear bacteriuria in approximately 40% of patients 5, 4

Common Pitfalls

• Avoid treating based solely on positive urine culture or cloudy urine appearance - this represents colonization in most cases and treating asymptomatic bacteriuria leads to antimicrobial resistance 3, 5
• Do not perform routine daily bacteriologic monitoring - only 2% of symptomatic episodes are potentially preventable through such monitoring 7
• Avoid prophylactic antimicrobials at the time of routine catheter replacement 3
• Do not add antimicrobials or antiseptics to the drainage bag - randomized trials show no benefit 3