Catheter-Related Bacteriuria

Long-term urinary catheterization results in bacteriuria, which may lead to symptomatic UTI and other complications. Avoiding or promptly discontinuing catheter use as soon as possible is recommended.

Catheter-related bacteriuria in the elderly represents the most common nosocomial infection; about 15 to 30% of hospitalized elderly patients with acute conditions undergo urinary catheterization. Indwelling urinary catheterization causes bacteriuria to occur at a rate of 3 to 10% of patients per day; a single in-and-out catheterization may cause bacteriuria in as many as 20% of patients. By about 30 days (the conventional cutoff between short- and long-term catheterization), most patients are bacteriuric. At any given time, an estimated 100,000 elderly nursing home residents have long-term indwelling urinary catheters. Bladder calculi can also result in sustained bacteriuria that is difficult to treat even with antibiotics. Development of bacteriuria is facilitated by poorly controlled diabetes mellitus, because increased urine glucose levels provide the substrate for bacterial growth.

Etiology and Pathogenesis

Bacteriuria associated with short-term catheterization usually involves a single uropathogen, most commonly E. coli; bacteriuria associated with long-term catheterization is characteristically polymicrobial, usually with two to five isolates, including E. coli, P. mirabilis, K. pneumoniae, Enterococcus, Providencia stuartii, and M. morganii. Several other bacterial pathogens and yeasts have also been implicated.

Bacteria often gain access into the urinary tract from periurethral colonization by the patient's colonic flora; migration between the catheter and uroepithelium into the bladder and the upper urinary tract may occur. Rarely, uropathogens may be introduced from breaks in the integrity of the closed collection system; furthermore, the bacteria are capable of colonizing the intraluminal surface of the catheter and bag with subsequent proximal migration against the urinary flow into the urinary tract.

Complications

The most common complication of catheter-related asymptomatic bacteriuria is symptomatic infection (which can cause fever, delirium, pyelonephritis, bacteremia, urosepsis, death). In addition, long-term catheterization may give rise to urethritis, urinary calculi, epididymitis, vesicoureteral reflux, chronic pyelonephritis, and chronic tubulointerstitial nephritis with deformed calyces and scarring of the renal parenchyma.

Diagnosis and Prevention

Urine cultures obtained from the lumen of urinary catheters often contain more species than are actually present in the bladder; removal of the catheter and replacement with a new catheter before obtaining cultures are often recommended.

Every attempt must be made to minimize the duration of short-term catheterization and to avoid long-term catheterization. Criteria for the use of long-term catheterization are listed in Table 100-2. Maintenance of the integrity of the closed urinary system is also of utmost importance.

The use of bladder irrigation, the addition of antibacterial chemicals in collection bags, the use of silver-coated catheters, and the use of methenamine to reduce bacteriuria have shown equivocal results.

Treatment

The need to treat asymptomatic bacteriuria in catheterized elderly patients is not supported by current data. Antibiotic use may delay the onset of bacteriuria in short-term catheterization but does not reduce complications; antibiotic use may also promote growth of resistant uropathogens.

Symptomatic UTI associated with short-term and long-term catheterization should be treated with the narrowest spectrum antibacterial drug pending urine culture and sensitivity results. The duration of treatment depends on the clinical scenario; a 7- to 14-day regimen is suggested for most cases. Empiric therapy for symptomatic UTI associated with long-term catheterization (when resistance is not suspected and the patient is not critically ill) should include antibiotics active against likely polymicrobial flora (eg, TMP-SMX or a 2nd- or 3rd-generation cephalosporin). For seriously ill patients, a two-drug combination of ampicillin (to cover enterococci) plus a 3rd-generation cephalosporin, aztreonam, an aminoglycoside, or a quinolone is recommended. Some experts recommend removing and replacing the catheter.