Overview: Catheter-related urinary tract infection (UTI) occurs because urethral catheters inoculate organisms into the bladder and promote colonization by providing a surface for bacterial adhesion and causing mucosal irritation. The presence of a urinary catheter is the most important risk factor for bacteriuria.
Once a catheter is placed, the daily incidence of bacteriuria is 3 to 10%. Between 10% and 30% of patients who undergo short-term catheterization (i.e., 2 to 4 days) develop bacteriuria and are asymptomatic. Between 90% and 100% of patients who undergo long-term catheterization develop bacteriuria.
About 80% of nosocomial UTIs are related to urethral catheterization; only 5 to 10% are related to genitourinary manipulation. The presence of potentially pathogenic bacteria and an indwelling catheter predisposes to the development of a nosocomial UTI. The bacteria may gain entry into the bladder during insertion of the catheter, during manipulation of the catheter or drainage system, around the catheter, and after removal.
The following is a review of the catheter-associated complications encountered with indwelling urinary catheters.
Bacteriuria (bacteria in the urine) usually occurs in most patients who have a catheter in place for 2 to 10 days. A large number and a variety of types of organisms are present in the periurethral area and in the distal part of the urethra that may be introduced into the bladder at the time of catheter insertion.
Other factors that increase the risk of bacteriuria include the presence of residual urine because of inadequate bladder drainage in the bladder (urine stasis promotes bacterial growth), ischemic damage to the bladder mucosa through overdistention, mechanical irritation from the presence of a catheter, and biofilm formation on the catheter intraluminal surface.
Most bacteria causing CAUTI gain access to the urinary tract either extraluminally or intraluminally.
Extraluminal contamination may occur as the catheter is inserted, by contamination of the catheter from any source. Extraluminal contamination is thought to also occur by microorganisms ascending from the perineum along the surface of the catheter. Most episodes of bacteriuria in catheterized women are believed to occur through the extraluminal entry of organisms. Fecal strains contaminate the perineum and urethral meatus, and then ascend to the bladder along the external surface to cause bacteriuria, catheter biofilm formation, and encrustation. Intraluminal contamination occurs by ascent of bacteria from a contaminated catheter, drainage tube, or urine drainage bag.
Microorganisms can migrate up the catheter into the bladder within 1 to 3 days.
At least 66% of CAUTIs result from extraluminal contamination, whereas 34% are a result of the intraluminal route.
There are three catheter-associated entry points for bacteria:
1. the urethral meatus, with the introduction of bacteria occurring on insertion of the catheter,
2. the junction of the catheter-bag connection, especially when a break in the closed catheter system occurs, or
3. the drainage port of the collection bag.
All 3 of these mechanisms involved in the pathogenesis of colonization and infection of the urinary tract combine to make CAUTI very difficult to prevent in individuals with urinary catheters in place for longer than 2 weeks.
Two catheter hygiene principles should be used to prevent bacteriuria:
1. a “closed” system should be used, and
2. the catheter should be removed as soon as possible.
A systematic review suggested that sealed (e.g., taped, presealed) drainage systems contribute to preventing bacteriuria.
The basic components of a closed system include the catheter, a preconnected collecting tube with an attached sampling port, and a vented drainage bag with a port for drainage.
Catheter-associated bacteriuria is usually asymptomatic and uncomplicated, and gradually resolves in an otherwise normal urinary tract after the catheter is removed.
The most severe and common catheter-associated complication, which can lead to urosepsis and septicemia, involves CAUTIs, the most common nosocomial infections in hospitals and nursing homes, comprising more than 40% of all institutionally acquired infections.
CAUTIs are considered complicated urinary tract infections (UTIs) and are the most common complication associated with long-term catheter use.
CAUTIs may occur at least twice a year in patients with long-term indwelling catheters, requiring hospitalization. They are associated with increased urosepsis, septicemia, and mortality. Catheters are a good medium for bacterial growth because bacterial biofilms (layers of organisms) adhere to the many surfaces of the catheter system. CAUTI is more likely to occur in women than men; because of the shorter female urethra and because of the urethra’s close proximity to the anus, bacteria have a shorter distance to travel. Most CAUTIs involve multiple organisms and resistant bacteria from catheter-associated biofilms (discussed later). These include Enterobacteriaceae other than E. coli (e.g., Klebsiella, Enterobacter, Proteus, and Citrobacter), pseudomonas aeruginosa, enterococci and staphylococci, and Candida. Candiduria is especially common in individuals with prolonged urinary catheterization receiving broad-spectrum, systemic antimicrobial agents.
Due to increased antibiotic use, there has been an increase in antibiotic-resistant microorganisms, particularly P. aeruginosa and C. albicans, two organisms frequently involved in device-associated nosocomial infections. A problem in hospitals and LTC facilities is infection with vancomycin-resistant Enterococcus (VRE) and methicillin-resistant staphylococcus aureus (MRSA). In patients with long-term indwelling urinary catheters, symptoms of catheter-related infection are often nonspecific. Symptoms of a UTI are caused by an inflammatory response of the epithelium of the urinary tract to invasion and colonization by bacteria. Among catheterized individuals, clinical manifestations of UTI (pain, urgency, dysuria, fever, and leukocytosis) are uncommon even when bacteria or yeast is present, and are no more prevalent with positive urine culture results than with negative results.
Confusion or unexplained fever may be the only symptoms of catheter-related CAUTI in patients residing in nursing homes.
Diagnosing catheter-related infection in patients with spinal cord injury (SCI) may be especially challenging from history and physical examination because of a frequent lack of localizing symptoms. Often, the only symptom of catheter-related UTI in individuals with SCI is fever, diaphoresis, abdominal discomfort, or increased muscle spasticity.
Once an indwelling urinary catheter is inserted, bacteria quickly develop into colonies known as biofilms (living layers) that adhere to the catheter surface and drainage bag.
A biofilm is a collection of microorganisms with altered phenotypes that colonize the surface of a medical device such as an indwelling urinary catheter.
Urine contains protein that adheres to and primes the catheter surface. Microorganisms bind to this protein layer and thus attach to the surface. Such bacteria are different from free-living planktonic bacteria (bacteria that float in urine). Urinary catheter biofilms may initially be composed of single organisms, but longer exposures inevitably lead to multiorganism biofilms. Bacteria in biofilms have considerable survival advantages over free-living microorganisms, being extremely resistant to antibiotic therapy.
The link between biofilm and infection is that the biofilm provides a sustained reservoir for microorganisms that, after detachment, can infect the patient. These biofilms cause further problems if the bacteria (e.g., P. mirabilis) produce the enzyme urease.
The urine then becomes alkaline (increased pH), causing the production of ammonium ions, followed by crystallization of calcium and magnesium phosphate within the urine. These crystals are then incorporated into the biofilm, resulting in encrustation of the catheter over a period of time.
Several features of biofilms have important implications for the development of antimicrobial resistance in organisms growing within the biofilm. Because the presence of the biofilm inhibits antimicrobial activity, organisms within the biofilm cannot be eradicated by antimicrobial therapy alone. The urinary biofilm provides a protective environment for the microorganisms, which allows evasion of the activity of antimicrobial agents. The biofilm also allows for microbial attachment to catheter surfaces in a manner that does not allow for removal with gentle rinsing, such as irrigation. Biofilms can begin to develop within the first 24 hours after catheter insertion. Biofilms have reportedly become so thick in some circumstances as to block a catheter lumen. The presence of urinary catheter biofilms has important implications for antimicrobial resistance, diagnosis of UTIs, and the prevention and treatment of CAUTIs.
Mineral deposition within the catheter biofilm causes encrustations, which are unique to biofilms formed on urinary catheters. Encrustations are seen typically on the inner surface of the catheter and can build to block catheter flow completely. They can coat the balloon, making it hard to deflate. Once the balloon is deflated, they fall off into the bladder.
Encrustation is generally associated with long-term catheterization, because it has a direct relationship with the duration of catheterization. Some patients are more prone to persistent catheter encrustation, and these patients are referred to as “blockers” as opposed to “nonblockers.” As noted previously, an alkaline urinary pH is an important factor in causing catheter encrustation.
Urosepsis can result from a UTI, leading to generalized sepsis, and death from severe UTIs has been reported. Mortality has been documented as more than 3 times higher in catheterized than in noncatheterized individuals.
Urethral damage occurs primarily in men because the catheter may interfere with drainage of seminal secretions. Urethral catheterization in men is associated with epididymitis, orchitis, scrotal abscess, prostatitis, and prostatic abscess. It can start at the time of insertion of the catheter but increases with long-term catheter use.
Difficulty passing the catheter may mean that the catheter has encountered a urethral stricture, has entered or created a false passage in the urethra, or that its passage is blocked by an obstructing prostate, bladder neck, or sphincter. The catheter may turn on itself and curl in the urethra.
Other complications associated with indwelling catheter use include the following:
In a study at a Veterans Affairs (VA) Medical Center, 42% of catheterized patients surveyed reported that the indwelling catheter was uncomfortable, 48% complained that it was painful, and 61% noted that it restricted their activities of daily living.
Of survey respondents, 30% stated that the catheter’s presence was embarrassing, and in unsolicited comments supplementing the structured questionnaires, 2 respondents noted that it “hurts like hell.”
Indwelling catheters can restrict activities and hinder rehabilitation in many individuals.
The following educational session is part I of a 3-part series on the subject of catheter-associated urinary tract infections. In this webinar, catheter-associated urinary tract infection as a part of the overall issue of hospital-acquired infection is examined. Why CAUTI is important and why this specific HAI has the attention of so many organizations and agencies is discussed. Finally, it examines the risk factors and pathogenesis for CAUTI, and what the current CDC definition of CAUTI is.
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