Catheter-Associated Urinary Tract Infections in Adults: Diagnosis, Treatment, and Prevention

Bacterial biofilm can form on the inner and outer surfaces of an indwelling urinary catheter following its insertion and can be associated with bacteriuria and CAUTI.^22,23 The biofilm comprises bacteria from the periurethral area that migrate upwards from a colonized drainage system. Bacteria present in the biofilm tend to exhibit slow growth, are protected from antibiotic exposure, and have less susceptibility to these agents.^22-24 When a mature biofilm has formed, catheter removal may be necessary for source control and to facilitate effective antimicrobial treatment. The pathogens that most commonly cause CAUTIs are Escherichia coli (23.9%), Pseudomonas aeruginosa (10.3%), and Klebsiella pneumoniae/oxytoca (10.1%).²⁵ Although urine cultures often grow yeast, particularly Candida spp., nonbacterial pathogens rarely cause UTI.

The risk of developing a CAUTI is directly related to catheter dwell time.^26,27 For catheterized patients, the rate of development of catheter-associated bacteriuria is approximately 3% to 7% per day^14,28 and is more common in the elderly and females. The likelihood of bacteriuria approaches 100% if a patient has an indwelling urinary catheter for ≥30 days,^27,29,30 which is part of the rationale for why a urine culture alone is not sufficient to diagnose a CAUTI. While bacteriuria is a risk factor for UTI, the frequency of progression from bacteriuria to CAUTI is low and treating ASB does not decrease the risk of future CAUTI. Other risk factors for the development of CAUTI include urinary tract instrumentation, diabetes mellitus, and malnutrition.^31,32

The two most important factors that lead to the development of CAUTIs and have been the main focus of quality improvement areas are unnecessary urinary catheter placement and inappropriate delay in removing a catheter when it is no longer needed.^26,33 Unfortunately, 38% of attending physicians are unaware that their patients have a urinary catheter in place.³⁴ Furthermore, in 20% to 50% of cases, there is no clear indication for catheter placement.^2,34

A CAUTI diagnosis is typically one of exclusion, as most patients present with fever and no apparent alternative source.^14,29 Since catheterized patients may not exhibit common cystitis symptoms,²⁹ most who develop CAUTI present with fever alone. However, most fevers in patients with bacteriuria and catheters are not CAUTIs and can be attributed to other sources. If a patient with an indwelling urinary catheter develops a fever and there is a suspicion of a CAUTI, careful evaluation is warranted for alternative sources of infection. This particularly applies to patients with severe systemic illness, such as hypotension or systemic inflammatory response syndrome, since these are unusual manifestations of CAUTI. The presence of either cloudy or malodorous urine does not indicate a UTI, and should not be the sole rationale for obtaining a urine culture.

Diagnostic workup of fever should include a clinical assessment of the patient. Indeed, professional guidelines recommend against obtaining a urine culture routinely for fever, unless invasive UTI risk is elevated, such as in patients with neutropenia, history of renal transplantation, or recent genitourinary surgery.³⁵ Diagnostic stewardship, focusing on the appropriate use of urine cultures, can reduce CAUTI rates.³⁶ For catheterized patients, hospitals are increasingly adopting reflex urine culture, where urine is simultaneously collected for a urinalysis and urine culture, but a urine culture is performed only if the urinalysis is positive for a predetermined threshold for pyuria, leukocyte esterase, or both. However, the use of reflex urine cultures remains an area of debate.³⁷ In addition, the Infectious Diseases Society of America recommends against screening for or treating ASB in patients with either short-term (<30 days) or long-term indwelling urethral catheters.²¹

Ideally, a urine culture should be obtained by collecting a midstream sample. In catheterized patients, a sample should be obtained after removal of the catheter; or, in patients with a clinical indication for ongoing catheterization, a sample should be obtained after a new catheter has been placed.¹⁴ If an indwelling urinary catheter must be continued, the recommendation is to disinfect the drainage system’s aspiration port and then obtain a urine culture. Urine should never be obtained from a catheter collection bag. (Table 2 summarizes best practices for diagnosis of CAUTI).