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Risk Factors

The urinary catheter is an extremely useful device but a nosocomial infection hazard. More than four decades ago, in an editorial entitled “Case against the Catheter,” the importance of the urinary catheter was noted and its dangers emphasized. Today, the urinary tract is still the most common site of nosocomial infection, accounting for approximately 40% of infections.
The two most effective measures to prevent nosocomial urinary tract infections—decreasing the duration of catheterization and use of a closed, sterile drainage system—were described three decades ago. Approximately 85% of cases of urinary tract infections are catheter-associated, and another 5% follow other types of urologic instrumentation, such as cystoscopy. Prevalence studies show that about 10% of patients in acute care hospitals have a urinary catheter; in an ICU, the rate of urinary catheter use is even higher.
Nosocomial urinary tract infections vary from asymptomatic conditions that resolve spontaneously on catheter removal to infections associated with complications that include pyelonephritis, bacteremia, perinephric abscess, renal stones, renal failure, and death. Bloodstream invasion occurs at a rate of nearly 3% among cases of nosocomial bacteriuria. The rate of bacteremia in patients with a Serratia urinary tract infection was four times that of patients with nosocomial urinary tract infections caused by other organisms. Bacteremia developed in men with nosocomial urinary tract infections twice as often as in women. In fact, the urinary tract is the most common portal of entry for bacteria in patients with gram-negative bacteremia. The mortality rate of bacteremia from a catheter-associated urinary tract infection is estimated to be 10% to 30%. In one study, the mortality was three times higher among patients with nosocomial bacteriuria than in uninfected controls, although bacteremias were not documented in the group with the increased mortality rate. In a subsequent study, a marked reduction was noted in the frequency of infections and death rate after introduction of a catheter bag drainage system that did not disconnect at the junction of the catheter and collection tube. Other investigators in a case-control study found no relationship between nosocomial urinary tract infections and death.
Risk Factors
A number of factors are associated with an increased rate of catheter-associated nosocomial bacteriuria, including female sex, age above 50 years, and the presence of a rapidly progressive, fatal underlying illness. Using an aseptic technique during catheter insertion and maintaining a closed, sterile drainage system are key factors in determining the incidence of bacteriuria. The average rate of acquisition of bacteriuria is 5% to 10% for each day of catheterization; thus, after 10 days, about 50% of patients have bacteriuria. Breaks in the closed drainage system and improper care of the drainage bag occurred in 30% of catheterized patients. Other investigators found that in patients whose urinary catheters had sealed catheter-drainage tube junctions that could not be disconnected, the rate of infection was nearly three times lower than in patients assigned to catheters with unsealed junctions.
Systemic antimicrobials can decrease the rate of bacteriuria but are effective only for the initial 4 days of catheterization. When infection does occur in patients receiving systemic antimicrobials, however, the organisms isolated are generally more resistant. Having more than one patient with a urinary catheter in a room is another risk factor. This is especially a problem if one patient already has bacteriuria, because the hands of medical personnel have been shown to spread organisms from one drainage bag to another.
Organisms appear to enter the urinary tract by one of three routes: (a) from the urethra into the bladder by way of the catheter, (b) at the urethral meatus around the catheter, or (c) by an intraluminal route from the drainage bag or the junction between the catheter and collecting tube during a disconnection. The majority of infections result when bacteria ascend from the periurethral area by means of a thin layer of fluid on the outside of the catheter at the catheter-meatal junction or by the intraluminal route during disconnection of the junction between the catheter and the collection tube. Studies have emphasized the importance of the meatal route in the pathogenesis of bacteriuria; 70% of catheterized patients acquire bacteriuria with the same organism isolated from the urethral meatus before the development of bacteriuria. In another study assessing the importance of prior urethral and rectal colonization in the pathogenesis of catheter-associated bacteriuria, prior urethral colonization was observed in 67% of women and 29% of men in whom bacteriuria developed. Antecedent rectal colonization was noted in 78% of women and 29% of men. In catheterized women, the majority of episodes of bacteriuria develop through the periurethral route, and the source is usually the rectal flora. In contrast, in male patients, most infections develop via the intraluminal route; the source of bacteria is not the rectum but rather cross-infection. This study suggests that different prevention strategies may be needed for male and female patients.
Escherichia coli is the most common cause of nosocomial bacteriuria, accounting for about one third of infections. Other common pathogenic agents are Proteus species (15%), Klebsiella species (10%), Pseudomonas species (10%), Enterobacter species (5%), enterococci (10% to 15%), and Candida (5%). Other organisms, such as Serratia and Providencia, account for the remaining 7% to 12%. In general, the organisms responsible for nosocomial bacteriuria are more resistant to antimicrobials than are the strains that cause community-acquired infections. The patient’s own gastrointestinal flora is the source of many gram-negative bacilli that cause catheter-associated infections. Outbreaks of nosocomial urinary tract infections have been linked to contaminated rectal thermometers, cystoscopes, irrigation solutions, and disinfectants. Medical personnel who do not wash their hands after caring for each patient can transmit gram-negative bacilli from one urinary drainage bag to another.
The diagnosis of a nosocomial urinary tract infection in a catheterized patient is based on a urine culture showing significant bacteriuria. Formerly, counts of more than 105 colony-forming units (CFU) per milliliter were required to establish a diagnosis; however, according to a study by Maki and associates, counts as low as 102 CFU/mL are probably significant and should not be ignored. Low-level counts of bacteria or Candida in the urine usually increase within 3 days to concentrations above 105 CFU/mL. When a urinary tract infection is responsible for fever, pyuria (more than five white cells per high-power field) should be present. One or more organisms per oil-immersion field in a Gram’s-stained drop of unspun urine may provide a clue to the identity of the pathogen and help guide the initial selection of antimicrobial therapy. Polymicrobial bacteriuria occurs in about 75% of patients with long-term indwelling urethral catheters, with a mean of more than two organisms per specimen. The duration of bacteriuric episodes varies with each species. Gram-positive organisms such as coagulase-negative staphylococci persist for about 1 week, whereas Providencia stuartii may be present for 10 weeks or longer. Routine bacteriologic monitoring of urine from asymptomatic catheterized patients, however, is not a cost effective approach to decrease or predict the frequency of symptomatic, catheter-related urinary tract infections.
The clinical features of nosocomial bacteriuria in a catheterized patient vary; the patient may have no symptoms or may have chills, fever, flank pain, oliguria, disseminated intravascular coagulation, or shock. Lower urinary tract symptoms such as frequency and dysuria are absent. In elderly catheterized patients, manipulation and change of the urinary catheter are frequent predisposing factors of urosepsis. In this group of patients, gastrointestinal complaints may predominate and direct attention away from the urinary tract.
All patients with a symptomatic, catheter-related urinary tract infection should be treated with a drug to which the causative organism is susceptible. If possible, the catheter should be removed or changed. The optimal duration of therapy is unknown, and the patient should be treated at least until the symptoms resolve if the catheter remains in place. For patients with a secondary bacteremia, which indicates a renal or prostatic source, drugs should be used that provide adequate levels in both urine and serum. Patients who have candiduria without candidemia may respond to catheter removal alone, amphotericin B bladder irrigation, or fluconazole. If clinical evidence of systemic candidiasis is lacking and there is no indication that pyelonephritis is present, then amphotericin B bladder irrigation may be tried if the catheter cannot be removed. Amphotericin B bladder irrigation consists of infusion of 5 to 10 mg of amphotericin B in 250 mL of sterile water into the bladder once daily; the catheter is cross-clamped for 1 hour. The appropriate duration of therapy is unknown, but 2 to 7 days is usually adequate. Most Candida organisms are susceptible to less than 1 µg of amphotericin B per milliliter, and the concentrations achieved with the suggested mixture are 20 to 40 µ/mL. Amphotericin B can also be given by continuous bladder irrigation over 12 hours; 25 mg of drug in 500 mL of 5% dextrose in water or sterile water is infused at a rate of 42 mL/h. In patients without renal insufficiency, fluconazole can be given at a dosage of 200 mg orally followed by 100 mg once daily for 4 days. Fluconazole is preferred for therapy of candiduria.
Generally, patients with catheter-associated bacteriuria who are asymptomatic do not require therapy because of the risk of selecting for resistant organisms. One exception may be patients with asymptomatic bacteriuria and a prosthetic graft or heart valve; such patients are at risk for seeding of the foreign body. The most effective measure is to remove the catheter and, if the urine culture remains positive, then treat the patient. In patients without prosthetic devices, the management of catheter-acquired bacteriuria after catheter removal is controversial. In one report, patients often became symptomatic after the catheter was removed. A single dose of oral trimethoprim-sulfamethoxazole (TMP-SMX) after catheter removal was usually effective in preventing symptomatic disease, particularly in patients less than 65 years old.
Recommendations by the Centers for Disease Control to prevent catheter-related bacteriuria are listed in Table 58-1. Using a closed, sterile drainage system and enforcing hand washing before and after a urinary catheter or drainage bag is handled are two mea-sures to prevent nosocomial bacteriuria. The use of meatal disinfectants such as a povidone-iodine solution or silver sulfadiazine cream, antimicrobial-impregnated catheters, silver oxide-coated catheters, antibacterial urethral lubricants, and antibacterial bladder irrigation has failed to decrease the incidence of bacteriuria. The addition of disinfectants such as hydrogen peroxide to the drainage bag is not effective in reducing the incidence of catheter-related bacteriuria.

Table 58-1. Summary of recommendations for prevention of catheter-associated urinary tract infections

The value of prophylactic systemic antimicrobials in preventing or delaying bacteriuria remains unclear. The possible benefits must be balanced against cost, adverse effects, and selecting for resistant flora. In one study, there was no benefit from the use of TMP-SMX to reduce the incidence of urinary tract infections in patients with long-term indwelling catheters. Resistant organisms such as Pseudomonas aeruginosa and P. stuartii were identified more often in the antimicrobial-treated group than in the control group. For selected patients, condom catheters can be used to prevent nosocomial bacteriuria. Condoms, however, can produce gangrene and serve as reservoirs for resistant bacteria. The technique of intermittent catheterization appears effective, but controlled studies evaluating this approach are necessary. Hospital-acquired urinary tract infections cause considerable patient suffering and economic loss, and new approaches to dealing with this common problem are needed. (N.M.G.)
Beeson PB. Case against the catheter. Am J Med 1958;24:1.
Breitenbucher RB. Bacterial changes in the urine samples of patients with long-term indwelling catheters. Arch Intern Med 1984;144:1585.
Neither monthly cultures nor prophylactic TMP-SMX was of value.
Bryan CS, Reynolds KL. Hospital-acquired bacteremic urinary tract infection: epidemiology and outcome. J Urol 1984;132:494.
Mortality was 31% and related to the severity of the underlying disease.
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Bacteriuria, particularly in female patients, was associated with improper suspension of the drainage bag.
Burke JP, et al. Prevention of catheter-associated urinary tract infections: efficacy of daily meatal care regimens. Am J Med 1981;70:655.
Daily meatal care was of no benefit in preventing bacteriuria.
Classen DC, et al. Daily meatal care for prevention of catheter-associated bacteriuria: results using frequent applications of polyantibiotic cream. Infect Control Hosp Epidemiol 1991;12:157.
Use of an antimicrobial cream containing polymyxin B, neomycin, and gramicidin applied to the urethral meatus three times daily did not reduce the rate of bacteriuria.
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Women with catheter-related bacteriuria have a rectal source more often than men do.
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In an experimental study, hand washing with a bland soap did not prevent transfer of bacteria from the groin to the catheter. Use of an isopropyl alcohol hand rinse was more effective in preventing hand transfer of gram-negative bacteria.
Filice GA, et al. Nosocomial febrile illnesses in patients on an internal medicine service. Arch Intern Med 1989;149:319.
Pneumonia and urinary tract infection were the two most common causes for nosocomial fever in patients on the medical service.
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Patients with candiduria should be evaluated for possible candidemia or a deep-seated infection.
Garibaldi RA, et al. Factors predisposing to bacteriuria during indwelling urethral catheterization. N Engl J Med 1974;291:215.
Risk factors are outlined. Antimicrobials were effective during the initial 4 days of catheterization.
Garibaldi RA, et al. Meatal colonization and catheter-associated bacteriuria. N Engl J Med 1980;303:316.
Bacteria can often be isolated in the periurethral space before the development of bacteriuria.
Garibaldi RA, et al. An evaluation of daily bacteriologic monitoring to identify preventable episodes of catheter-associated urinary tract infection. Infect Control 1982; 3:466.
Daily urine cultures do not reduce the incidence of symptomatic, catheter-related urinary tract infections.
Gleckman R, et al. Catheter-related urosepsis in the elderly: a prospective study of community-derived infections. J Am Geriatr Soc 1982;30:255.
Usually a polymicrobial infection. A traumatic catheter event often precedes the acute symptomatic episode.
Haley RW, et al. The nationwide nosocomial infection rate. Am J Epidemiol 1985; 121:159.
Nosocomial urinary tract infections accounted for 42% of all infections.
Hamory BH, Wenzel RP. Hospital-associated candiduria: predisposing factors and review of the literature. J Urol 1978;120:444.
Key risk factors include increased duration of catheterization and use of multiple antimicrobials.
Harding GKM, et al. How long should catheter-acquired urinary tract infection in women be treated? A randomized, controlled study. Ann Intern Med 1991;114:713.
After catheter removal, asymptomatic bacteriuria frequently becomes symptomatic. Single-dose therapy with oral TMP-SMX was effective after short-term catheter use.
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Cooperative patients with condom catheters had lower rates of urinary tract infections than did patients with indwelling catheters.
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Meatal care with silver sulfadiazine cream did not reduce the rate of bacteriuria.
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Both amphotericin B bladder irrigation and oral fluconazole were effective treatments for patients with candiduria.
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Long-term use of a condom catheter drainage system was associated with urinary tract infections and penile complications.
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Overall, no reduction in the rate of bacteriuria was noted with use of the silver oxide-coated catheter except for women not receiving antimicrobials.
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Bacteremia developed in almost 39% of patients with nosocomial bacteriuria.
Kunin CM, Finkelberg Z. Evaluation of an intraurethral lubricating catheter in prevention of catheter-induced urinary tract infections. J Urol 1971;106:928.
Classic. Ineffective approach to preventing urinary tract infections.
Kunin CM, McCormack RC. Prevention of catheter-induced urinary tract infections by sterile closed drainage. N Engl J Med 1966;274:1155.
Leu HS, Huang CT. Clearance of funguria with short-course antifungal regimens: a prospective, randomized, controlled study. Clin Infect Dis 1995;20:1152–1157.
Spontaneous clearance rate in the control group was 40%. Systemic regimens with amphotericin B or oral fluconazole were more effective than local irrigation with amphotericin B.
Maki DG, et al. Nosocomial urinary tract infection with Serratia marcescens: an epidemiologic study. J Infect Dis 1973;128:579.
An infected, catheterized patient should not share a room with another catheterized patient.
Platt R, et al. Mortality associated with nosocomial urinary tract infection. N Engl J Med 1982;307:637.
Nosocomial bacteriuria was associated with a threefold increase in mortality.
Platt R, et al. Reduction of mortality associated with nosocomial urinary tract infections. Lancet 1983;1:893.
Fewer infections and deaths were noted in the patients whose bladder catheters had preconnected, sealed junctions.
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Analysis supporting the use of sealed-junction catheters.
Riley DK, et al. A large, randomized clinical trial of a silver-impregnated urinary catheter: lack of efficacy and staphylococcal superinfection. Am J Med 1995;98: 349–356.
Silver-coated catheters were not effective in preventing bacteriuria.
Saint S, Elmore JG, Sullivan SD, Emerson SS, Koepsell TD. The efficacy of silver alloy-coated urinary catheters in preventing urinary tract infection: a meta-analysis. Am J Med 1998;105(3): 236–41.
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Guidelines for treating candiduria.
Stamm WE. Catheter-associated urinary tract infections: epidemiology, pathogenesis, and prevention. Am J Med 1991;91(Suppl 3B):65S.
Comprehensive review.
Stark RP, Maki DG. Bacteriuria in the catheterized patient. N Engl J Med 1984; 311:560.
Quantitative cultures showing fewer than 105 CFU per milliliter are significant.
Thompson RL, et al. Catheter-associated bacteriuria. JAMA 1984;251:747.
Instillation of hydrogen peroxide into the drainage bag did not prevent bacteriuria.
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Review. Closed catheter drainage is the only effective method to prevent bacteriuria.
Warren JW. Catheter-associated urinary tract infections. Infect Dis Clin North Am 1997;11:609–622.
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Among long-term elderly patients, acute inflammation of the kidneys was noted at autopsy in 38% of those with a urinary catheter, and in 5% of those without a catheter.
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Antimicrobial irrigation is not effective in preventing bacteriuria.
Warren JW, et al. A prospective microbiologic study of bacteriuria in patients with chronic indwelling urethral catheters. J Infect Dis 1982;146:719.
Of patients with long-term indwelling catheters, 98% had bacteriuria, which was usually polymicrobial (77%).


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