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Chapter 15. Prevention of Nosocomial Urinary Tract Infections
Sanjay Saint, M.D., M.P.H.
University of Michigan School of Medicine
Many hospitalized patients require the placement of indwelling urinary catheters for days or even weeks at a time.1 Only a minority of patients develop urinary tract infections because of the presence of these devices,2,3 but the frequency of their use produces substantial overall morbidity for patients and costs to the healthcare system. Urinary tract infections (UTIs) account for up to 40% of nosocomial infections,4,5 with urinary catheter-related infections causing the vast majority of nosocomial UTIs.6 Each hospital-acquired UTI adds approximately $675 to the costs of hospitalization. When bacteremia develops, this additional cost increases to at least $2800.2
Because of the substantial complications and costs associated with the use of urinary catheters, a number of practices have been evaluated in an effort to reduce the incidence of urinary catheter-related infections. This chapter reviews the evidence supporting the use of silver alloy coated urinary catheters, and, because of its similarity, the recently described practice of using urinary catheters impregnated with the antibiotic combination of minocycline and rifampin. Subchapter 15.2 reviews the evidence supporting the use of suprapubic catheters as an alternative to urethral catheters.
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Subchapter 15.1. Use of Silver Alloy Urinary Catheters
Silver is a highly effective antibacterial substance, which can be applied to various types of catheters. (See Subchapter 16.2 for a discussion of intravascular catheters coated with a combination of silver sulfadiazine and chlorhexidine). Multiple studies have suggested that silicone urethral catheters coated with hydrogel and silver salts reduce the risk of developing bacteriuria, compared with standard latex urethral catheters (Foley catheters). As shown in a recent meta-analysis, this benefit applies to catheters coated with silver alloy (which are coated on both internal and external surfaces of the catheter), but not silver oxide (which are coated on the external catheter surface only). Consequently, this chapter focuses only on studies evaluating silver alloy catheters, and the use of catheters coated with antimicrobials.8
Prevalence and Severity of the Target Safety Problem
Almost one million episodes of nosocomial UTI occur annually in the United States.9 Each year approximately 96 million urethral catheters are sold worldwide. Of these, nearly 25% are sold in the United States.3 The daily rate of bacteriuria in catheterized patients ranges from 3 to 10%, with the incidence directly related to the duration of catheterization.4 Among patients with bacteriuria, 10 to 25% will develop symptoms of local urinary tract infection,2,10 such as suprapubic or flank pain. The development of catheter-related bacteriuria carries with it a 2.8-fold increased risk of death, independent of other co-morbid conditions and disease severity.11,12 Bacteremia results from catheter-related bacteriuria in approximately 3% of patients, and invariably represents a serious complication.2,3
Beyond the morbidity and mortality associated with indwelling catheters, catheter-related infection results in substantially increased healthcare costs. Data suggest that each episode of hospital-acquired symptomatic catheter-related UTI costs an additional $676, and each episode of catheter-related nosocomial bacteremia costs a minimum of $2836.2
Estimates from one university hospital, based on data from almost 20 years ago, were that hospital-acquired UTI led to approximately $204,000 in additional expenses per year.13 More recent data are unavailable, but the institutional costs attributable to catheter-related infection are clearly substantial.
Opportunities for Impact
Since catheter-related UTI is the leading cause of nosocomial infection in the United States and is associated with increased morbidity and costs, any intervention that reduces the incidence of catheter-related UTI is potentially important. Currently, it is unknown what proportion of patients with indwelling catheters receives silver alloy catheters, however it is likely to be the minority.
As shown in Table 15.1.1, a meta-analysis which included 4 randomized clinical trials,14-17 compared the efficacy of silver catheters with standard, non-coated catheters. Five additional studies18-22 have appeared since publication of this meta-analysis. In 3 of these studies,18,20,22 the patient represented the unit of analysis. Another study employed a randomized crossover design (Level 1), randomizing wards rather than individual patients.19 The final study used a prospective, before-after design at 5 different hospitals (Level 2).21
The patient populations for these studies included patients on various hospital services including urology, internal medicine, neurology, and the intensive care unit. In general, the studies included patients expected to be catheterized for at least 2 days. Since the patients resided in acute care hospitals rather than extended care centers, most were catheterized for 10 days or less. Several studies specified that patients given concomitant antibiotics were excluded.15-18
The individual trials and the meta-analysis focused primarily on the surrogate outcome of bacteriuria (Level 2). The definition of bacteriuria varied somewhat in the studies. However, low-level growth from a catheterized specimen (i.e., 102 colony forming units (CFU) /mL) usually progresses within days to concentrations of greater than 104 CFU/mL unless antibiotic therapy is given.23 Unfortunately, none of the studies was adequately powered to detect a significant difference in the clinically more important outcomes of catheter-related bacteremia or death. Though bacteriuria is a surrogate endpoint,24 it is probably appropriate to use since it is a component of the only causal pathway in the disease process between catheterization and an important clinical outcome (e.g., symptomatic UTI or catheter-related bacteremia). One study did report differences in secondary bloodstream infections.19
Evidence for Effectiveness of the Practice
The 4 clinical trials14-17 of silver alloy catheters included in the meta-analysis7 all showed a significant reduction in the development of catheter-associated bacteriuria. As shown in Table 15.1.1, studies published after the meta-analysis have reported more mixed results. Several of the studies have shown a statistically significant benefit of silver alloy catheters, but with a smaller relative risk reduction compared to that reported in the meta-analysis.19,21,22 However, one study failed to find a significant benefit associated with silver alloy catheters,20 and another found benefit from silver alloy catheters in those given such catheters for about 5 days, but not in those given the catheter for 14 days.18 A formal update of the previous meta-analysis would be helpful, but is beyond the scope of the current report.
Potential for Harm
There is likely minimal harm from the use of silver alloy urinary catheters. The one theoretical harm involves the development of antimicrobial resistance. However, since silver is not used systemically in the form of an antimicrobial agent for treatment, the clinical significance of antimicrobial resistance to silver is unclear.
Costs and Implementation
Each silver alloy urinary catheter tray costs about $5.30 more than a standard, non-coated urinary catheter tray. However, a recent economic evaluation indicates that when all the clinical and economic costs are accounted for, silver alloy urinary catheters may provide both clinical and economic benefits in patients receiving indwelling catheterization for 2 to 10 days.3 It should be noted that one of the major assumptions made in the economic evaluation is that a certain proportion of patients with bacteriuria develop the clinically important (Level 1) outcomes of symptomatic UTI or bacteremia. The economic analysis did not assign any costs to bacteriuria but did assign costs if patients developed these clinically important outcomes. Additionally, several of the very recent efficacy studies of silver alloy catheters19,21,22 were not included in the economic analysis. A clinical study, adequately powered to detect both meaningful clinical and economic endpoints, would confirm the results of this economic evaluation that relied on modeling techniques. The overall cost of universal implementation of silver alloy catheters is unclear.
The data supporting the use of silver alloy urinary catheters to reduce urinary catheter-related bacteriuria is reasonably strong. As noted, the incidence of bacteriuria, while not extremely high, carries a high morbidity. It remains unclear whether silver alloy urinary catheters will also lead to decreases in the clinically more important outcomes of catheter-related bacteremia and mortality. Continuing investigation into the impact of silver alloy catheters on these important outcomes and their effect on the emergence of antibiotic resistance should be pursued. Of note, catheters coated with antibacterial substances other than silver have also been evaluated. A recent randomized study8 found that patients who received antimicrobial-impregnated catheters coated with minocycline and rifampin had significantly lower rates of gram-positive bacteriuria than a control group given standard, non-coated catheters (7.1% vs. 38.2%; p <0.001). Both control and intervention groups had similar rates of gram-negative bacteriuria and candiduria (Table 15.1.1). However, the theoretical risk of developing antimicrobial resistance to minocycline and/or rifampin (2 agents occasionally used systemically) may limit the use of catheters coated with these antibiotics.
Table 15.1.1. Studies of silver alloy and antibiotic-impregnated urethral catheters*
||Results: Odds or Risk of Bacteriuriaa
(unless otherwise noted)
||Meta-analysis of 4 randomized controlled trials (n=453) of silver alloy vs. uncoated urinary catheters
|OR 0.24 (95% CI: 0.11-0.52)
||Prospective, randomized, double-blind trial of silver alloy (n=407) vs. standard Foley (n=443) catheters
|RR 0.74 (95% CI: 0.56-0.99)
||Prospective, randomized study of medium-term catheterization with silver alloy (n=18) vs. silicone (n=17) catheters after radical prostatectomy
|After 14 days, 50.0% vs. 53.3% (p=NS)
|Prospective, randomized study of short-term catheterization with silver alloy (n=79) vs. latex (n=101) catheters
|On day 5, 6.3% vs. 11.9% (p<0.003)
||Prospective, blinded study of silver alloy vs. standard latex Foley catheters in 5 hospitals. Baseline period ranged from 3-12 months (mean, 8 months); intervention period ranged from 7-19 months (mean, 10 months)
Unadjusted infection rate: 4.5 vs. 7.1 infections per 1000 catheter days (p<0.01)
Adjusted infection rate: 4.9 vs. 8.1 infections per 1000 catheter days (p=0.13)
||12-month randomized crossover trial of catheter-associated urinary tract infections in patients with silver-coated and uncoated catheters. The ward was the unit of analysis. A cost analysis was also conducted.
Infection rate: 2.66 vs. 3.35 infections per 1000 patient-days, RR 0.79 (95% CI: 0.63-0.99)
Infection rate: 1.10 vs. 1.36 infections per 100 patients, RR 0.81 (95% CI: 0.65-1.01)
Infection rate: 2.13 vs. 3.12 infections per 100 catheters, RR 0.68 (95% CI: 0.54-0.86)
Estimated hospital cost savings with silver-coated catheters: $14,456 to $573,293
||Multicenter, prospective, randomized, double-blind trial of silver alloy (n=90) vs. standard (n=109) catheters in patients requiring catheterization for >3 days
After 10 days, 10% vs. 11.9%
OR 0.82 (95% CI, 0.30-2.20)
||Multicenter, prospective, randomized, blinded trial of medium-term catheterization (mean, 14 days) with minocycline-rifampin impregnated (n=56) vs. silicone (n=68) catheters after radical prostatectomy
Patients took longer to develop bacteriuria with antimicrobial- impregnated catheters than control catheters (p=0.006 by the log-rank test)
Overall bacteriuria at day 7: 15.2% vs. 39.7% (p<0.05)
Overall bacteriuria at day 14: 58.5% vs. 83.5% (p<0.05)
Gram-positive bacteriuria: 7.1% vs. 38.2% (p<0.001)
Gram-negative bacteriuria: 46.4% vs. 47.1% (p=NS)
Candiduria: 3.6% vs. 2.9% (p=NS)
* CI indicates confidence interval; NS, not statistically significant; OR, odds ratio; and RR, relative risk.
a Results are reported as intervention group (silver alloy or minocycline/rifampin catheter) vs. control group.
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