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URINARY CATHETER-RELATED INFECTIONS

URINARY CATHETER-RELATED INFECTIONS

Risk Factors
Pathogenesis
Etiology
Diagnosis
Treatment
Bibliography

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.
Pathogenesis
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.
Etiology
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.
Diagnosis
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.
Treatment
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.)
Bibliography
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Usually a polymicrobial infection. A traumatic catheter event often precedes the acute symptomatic episode.
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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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