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Health Care–Associated Urinary Tract Infections
Definitions
Health care–associated urinary tract infection (UTI) refers to UTI that is acquired while a patient is receiving medical treatment in a health care setting. The majority of health care–associated UTIs occur in patients whose urinary tracts are currently or were recently catheterized. All types of urinary catheters (indwelling, suprapubic, intermittent, and external or condom catheters) increase the risk of acquisition of bacteriuria and thus UTI. The focus of this chapter is on catheter-associated bacterial UTIs occurring in adults in hospitals and long-term care facilities (LTCFs). Candiduria, the most common type of health care–associated fungal UTI, is discussed in a separate section of the chapter.
There are major differences in the epidemiology, pathogenesis, treatment, and prevention of health care–associated UTI and acute uncomplicated cystitis, which are shown in Table 302.1 . Urinary tract infection is a nonspecific term that generally refers to symptomatic bacterial or fungal infection of the bladder or kidney, or both, in a patient. Although this term is often used without regard to the presence or absence of urinary symptoms, a strict definition of UTI requires the presence of symptoms related to the urinary tract ( Table 302.2 ). Unfortunately, catheter-associated bacteriuria is a nonspecific term frequently used in the urinary catheter literature that encompasses two more specific terms, catheter-associated asymptomatic bacteriuria (ASB) and catheter-associated urinary tract infection (CAUTI) . Catheter-associated bacteriuria is composed mostly of ASB, but in most publications one cannot discern what proportion of patients have CAUTI.
TABLE 302.1
Comparison of Uncomplicated Cystitis/Pyelonephritis and Health Care–Associated Urinary Tract Infections
| UNCOMPLICATED CYSTITIS AND PYELONEPHRITIS | HEALTH CARE–ASSOCIATED UTI | |
|---|---|---|
| Age | Younger | Older |
| Sex | Female, rare in males | Male and female, female predominance |
| Main risk factor | Intercourse | Urinary catheter |
| Pathogenesis | Fecal organisms ascend urethra to bladder | Extraluminal: fecal organisms ascend catheter-urethra interface to bladder |
| Intraluminal: fecal or exogenous (cross-infection) organisms enter drainage system that has been disconnected, ascend through catheter to bladder | ||
| Uropathogen virulence | More virulent: pyelonephritis > cystitis > ASB or fecal | Generally less virulent than in uncomplicated UTI |
| Microbiology | Single pathogen, usually Escherichia coli; yeast rare | Single (short-term catheter) to multiple (long-term catheter) organisms; diverse flora with gram-negatives, gram-positives, Candida spp. |
| Clinical | ASB in about 5% of women, but prevalence a function of culture frequency; transient, benign | Catheter-associated bacteriuria in about 5% per day of catheterization; >90% is ASB, usually persistent, most do not progress to CAUTI |
| Cystitis: dysuria, frequency, or urgency Pyelonephritis: fever, back pain/tenderness |
CAUTI: fever, delirium, other nonspecific signs/symptoms, may have no lower tract symptoms | |
| Diagnosis | ASB: ≥10 5 CFU/mL Cystitis/pyelonephritis: ≥10 3 CFU/mL |
Catheter-associated ASB: ≥10 5 CFU/mL CAUTI: ≥10 3 CFU/mL |
| Resistance | Common but predictable; fluoroquinolone and trimethoprim/sulfamethoxazole resistance increasing; ESBL uropathogens more common | Multidrug resistance common and less predictable; ESBL uropathogens and fluoroquinolone resistance common; CRE uropathogens still uncommon in most places. |
| Treatment | Short-course (single-dose to 5-day regimen, depending on drug) | 5- to 10-day regimen, depending on severity |
| Prevention | Education about risk factors; abstinence; antimicrobial prophylaxis | Reduce urinary catheterization; use condom or intermittent vs. indwelling urethral catheter; strict closed system with indwelling urethral catheter |
| Public health | Strains spread via food chain and within family units | Large reservoir of multidrug-resistant uropathogens; cross-infection a concern |
ASB, Asymptomatic bacteriuria; CAUTI, catheter-associated urinary tract infection; CRE, carbapenem-resistant Enterobacteriaceae; ESBL, extended-spectrum β-lactamase; UTI, urinary tract infection.
TABLE 302.2
Definitions for Urinary Tract Infection Terminology
| TERM | DEFINITION |
|---|---|
| Urinary tract infection (UTI) | Nonspecific term that generally refers to symptomatic bacterial or fungal infection of the urinary tract |
| Acute, uncomplicated cystitis | Symptomatic cystitis in a person with no signs or symptoms suggestive of infection outside the bladder |
| Catheter-associated bacteriuria | Presence of significant bacteriuria a in a catheterized or recently catheterized patient without regard to the presence or absence of urinary symptoms |
| Catheter-associated asymptomatic bacteriuria (ASB) | Presence of significant bacteriuria a in a catheterized or recently catheterized patient without symptoms referable to the urinary tract |
| Catheter-associated UTI (CAUTI) | Presence of significant bacteriuria a in a catheterized or recently catheterized patient with symptoms or signs referable to the urinary tract |
| Catheter-associated funguria | Presence of funguria in a catheterized or recently catheterized patient. Fungal colony counts have not been shown to be meaningful in interpreting the significance of funguria. Catheter-associated funguria should be distinguished as asymptomatic or symptomatic. |
a Quantity of bacteria in the urine suggestive of infection rather than contamination (see text).
The relationship between ASB and CAUTI and other clinical outcomes remains unclear. Most patients with ASB do not progress to CAUTI, and factors that trigger a symptomatic event in patients with ASB are not known. Thus even though the presence of bacteriuria is presumably necessary for the development of CAUTI, the development of urinary symptoms must require some facilitating event(s), such as tissue invasion, that we do not yet understand. On the other hand, even if ASB itself is benign, there are several reasons that may justify efforts to prevent it. For example, it may predispose the person to CAUTI through a common pathogenic pathway, in which case interventions that prevent ASB would be expected to prevent CAUTI. Additionally, catheter-associated bacteriuria (mostly ASB) is the source of many episodes of health care–associated bacteremia and may be associated with increased mortality, although this latter point is controversial. In hospitals and LTCFs, catheter-associated bacteriuria represents a large reservoir of antimicrobial-resistant urinary pathogens in patients that increases the risk of cross-infection among catheterized patients. ASB also provides a scapegoat infection for physicians who have a low threshold for using antimicrobial therapy (inappropriately), and detection of ASB can terminate the diagnostic evaluation prematurely. The relationships between ASB and clinical outcomes, including CAUTI, are difficult to demonstrate in most studies, given the large sample sizes needed to demonstrate such a benefit.
Treatment of ASB is not recommended except in certain circumstances, such as pregnancy and urologic procedures that cause mucosal bleeding. Antimicrobial treatment of ASB, particularly in catheterized persons, typically leads only to short-term suppression of bacteriuria, and clearly increases the likelihood of emergence of resistant urinary organisms. Antimicrobial exposure also increases the patient's risk for developing Clostridioides difficile (formerly Clostridium difficile ) colitis. Bacteremia can arise from bacteriuria in patients with both ASB and CAUTI, and at this point it is not possible to predict which patients with bacteriuria will develop bacteremia. Therefore a policy of widespread treatment of ASB is likely to be detrimental rather than beneficial. On the other hand, prevention of ASB might lead to fewer episodes of CAUTI, bacteremia, fever episodes, cross-infection, and inappropriate antimicrobial use. In fact, the greatest impact of effective CAUTI prevention interventions may be that removing unnecessary urinary catheters will also prevent episodes of ASB, and their sequelae, rather than the few episodes of CAUTI that occur in these patients. The subset of patients who have an ongoing need for urinary catheters for bladder drainage will be persistently bacteriuric. In these patients, CAUTI prevention efforts should focus on avoiding overdiagnosing CAUTI in patients who are asymptomatic and thus have ASB.
Epidemiology
Incidence and Prevalence
Approximately 75% of UTIs acquired in the hospital are associated with urinary catheters. In one study of 1453 health care–associated, symptomatic UTIs, 72% were CAUTIs and 28% were not catheter associated. Almost half of the CAUTIs (45%) occurred among intensive care unit (ICU) patients. The National Healthcare Safety Network (NHSN) is the United States’ national health care infection surveillance system, maintained by the Centers for Disease Control and Prevention (CDC). Of note, the current NHSN surveillance and reporting for UTI includes only CAUTI, and the only catheter type that meets surveillance definitions is the indwelling urethral (Foley) catheter; UTIs not associated with indwelling urinary catheters and episodes of ASB are not reported. Despite national emphasis on decreasing CAUTI, CAUTI rates did not decrease between 2009 and 2014. Whether the lack of change relates to changes in the surveillance definitions, which have changed often, or to an overall decrease in use of urinary catheters, thus shrinking the denominator, is unclear. Per the 2015 NHSN report on device-related infections, which included data from calendar year 2013, the ratio of urinary catheter-days to patient-days decreased from the prior report in 2010.
Urinary catheters are placed for different reasons in acute-care facilities and LTCFs. Common indications for urinary catheter use in acute care are discussed later under “Reduction of Unnecessary Catheterization” (see Table 302.6 ). Most of these patients are catheterized for only 2 to 4 days. The most common appropriate reason for urinary catheterization in LTCFs is to relieve bladder outlet obstruction, and these catheters are often in place for years. Management of incontinence is no longer considered an appropriate justification for urinary catheterization.
The incidence of bacteriuria associated with indwelling urethral catheterization with a closed drainage system is approximately 3% to 8% per day and, thus, many patients catheterized for short periods of time and almost all those catheterized for a month or more will have catheter-associated bacteriuria. One month, or 30 days, is a convenient dividing line between short-term and long-term catheterization, and it is used as such in this chapter, except where stated otherwise.
NHSN data from 2013–2014 showed the mean incidence of CAUTI per 1000 catheterized days was 1.3% to 4.8% in adult critical care units, 1.3% in inpatient medical-surgical wards, 2.0% to 2.5% in long-term acute care hospitals, and 2.6% in inpatient rehabilitation facilities. Compared to data from 2012, CAUTI rates increased in the majority of critical care locations while decreasing in most non–critical care locations. Organisms causing CAUTI and reported to the NSHN are often resistant, with Escherichia coli fluoroquinolone resistance reported at 34.8% in 2014.
CAUTI Risk Factors
The duration of catheterization is the most important risk factor for the development of catheter-associated bacteriuria. Other risk factors for catheter-associated bacteriuria include the lack of systemic antimicrobial therapy, female sex, meatal colonization with uropathogens, microbial colonization of the drainage bag, catheter insertion outside the operating room, catheter care violations, absence of use of a drip chamber, rapidly fatal underlying illness, older age, diabetes mellitus, and elevated serum creatinine at the time of catheterization. Risk factors in patients with health care–associated UTIs not associated with catheterization include other forms of instrumentation of the urinary tract. Many noncatheterized patients with health care–associated UTI are probably also at increased risk for UTI in the community, due to host behavioral or genetic factors associated with increased risk for UTI.
Complications
Most episodes of catheter-associated bacteriuria occur in asymptomatic patients, with studies showing that less than one-fourth of patients with catheter-associated bacteriuria develop UTI symptoms. In one study of 235 new cases of catheter-associated bacteriuria, more than 90% of the patients were asymptomatic and afebrile. In another study of catheterized and bacteriuric female patients in an LTCF, the incidence of febrile episodes of possible urinary origin was only 1.1 episodes per 100 catheterized patient-days, and most of these episodes were low grade, lasted for less than a day, and resolved without antimicrobial treatment.
However, as noted previously, there are significant consequences of catheter-associated bacteriuria. Catheter-associated bacteriuria is the most common source of gram-negative bacteremia in hospitalized patients. Of 7217 episodes of bloodstream infection in acute-care hospitals across Canada, 21% were associated with the urinary tract; 71% of these episodes were associated with the presence of a urinary device. However, one study of 1497 newly catheterized hospitalized patients found that only 1 of the 235 episodes of catheter-associated bacteriuria was unequivocally associated with secondary bloodstream infection. Similarly, a retrospective cohort study of 444 episodes of catheter-associated bacteriuria in 308 patients found that only 3 episodes of bacteremia (0.7% of bacteriuric subjects) were directly attributed to bacteriuria. Both of these studies demonstrated that bacteremia in catheterized patients can arise from either CAUTI or ASB (i.e., with or without urinary tract symptoms). Risk factors for urinary catheter–associated bacteremia include male sex, immunosuppression, and urinary tract procedures. Urinary tract organisms are also the most common source of bacteremia in LTCFs, accounting for 40% to 55% of bacteremias, and bacteremia is often polymicrobial in these patients.
Patients undergoing long-term indwelling catheterization, in addition to almost universal polymicrobial bacteriuria, may develop symptomatic lower and upper UTI, bacteremia, frequent febrile episodes, catheter obstruction, renal and bladder stone formation associated with urease-producing uropathogens, local genitourinary infections, fistula formation, incontinence, and bladder cancer. Chronic renal inflammation and pyelonephritis are often found at autopsy in patients who had been on long-term urinary catheterization, many of whom were afebrile at the time of death. Catheter blockage can be a recurrent problem in long-term catheterized patients and results from encrustation formed by urease-producing organisms, especially Proteus mirabilis, which hydrolyze urea to ammonia with formation of struvite and apatite crystals in the catheter lumen.
The effect of catheter-associated bacteriuria, either CAUTI or ASB, on mortality remains controversial. Inability to fully adjust for confounding variables probably explains some of the association, because patients who require an indwelling catheter tend to be sicker or have comorbidities. A review and meta-analysis of the relationship of CAUTI (defined as bacteriuria) to mortality and length of stay in ICU patients found that CAUTI was associated with increases in both mortality and length of stay, but the significant association disappeared when the analysis was restricted to studies that adjusted for other predictors of mortality. Increased mortality has also been reported in residents of LTCFs with chronic indwelling catheters, but catheterized patients in long-term care also tend to be sicker and more functionally impaired.
One of the most serious adverse effects of catheter-associated bacteriuria is that bacteriuria is a frequent target for unnecessary antimicrobial therapy, which contributes to the problem of antimicrobial resistance in hospitals and LTCFs. Inappropriate treatment of ASB in hospitalized patients is well documented. For example, in a prospective, multicenter study of inpatients, 72% of 961 patients with ASB were treated with antimicrobial therapy unnecessarily. Of those treated inappropriately, 14% received over 14 days of antimicrobials. Inappropriate treatment is associated with older age, predominantly gram-negative bacteriuria, and pyuria. Inappropriate antimicrobial use also unnecessarily exacerbates the growing problem of health care–associated C. difficile colitis, by 8.5-fold in a study of ASB treatment in nursing homes. Catheter-associated bacteriuria is also harmful in that it comprises a large reservoir of antimicrobial-resistant organisms that may be transmitted between patients who have urinary catheters or other invasive devices.
Microbiology
Unlike the narrow and predictable spectrum of causative agents in uncomplicated UTI, a broad range of bacteria can cause health care–associated UTI, and many are resistant to multiple antimicrobial agents. Most episodes of bacteriuria in short-term catheterized patients are caused by single organisms, mostly gram-negative bacilli and enterococci. NSHN surveillance data from 2011 to 2014 provide the most comprehensive picture of the organisms causing CAUTI in acute-care, long-term acute care, and inpatient rehabilitation facilities. E. coli was the most common pathogen, accounting for 23% of 153,805 pathogens from CAUTIs reported in the surveillance network, although it is not as dominant as in uncomplicated UTI. The second-ranked pathogen was Candida albicans (11.7%). However, all species of Candida and unidentified yeast isolates from CAUTIs combined account for 23.9% of CAUTI pathogens. After 2015, CAUTI surveillance definitions changed to exclude yeast, reflecting the clinical uncertainty about whether Candida in the urine of catheterized patients represents infection or colonization. After Candida, the most commonly isolated bacterial pathogens, in order of relative rank, were Pseudomonas aeruginosa, Klebsiella pneumoniae/oxytoca, and Enterococcus faecalis. Other organisms reported include Proteus, Enterobacter, coagulase-negative Staphylococci, and Staphylococcus aureus. New gram-positive uropathogens that are rarely reported, yet have been identified through improved culture techniques or newly recognized as pathogens through microbiome studies of the bladder, include Actinotignum schaalii and Aerococcus urinae. Health care–associated UTIs arising from external catheters (condom drainage systems) are not reported to the NHSN, so less is known about their epidemiology. A single-center study of urine cultures collected from both indwelling and condom catheters in men found equivalent prevalence of Enterobacteriaceae and enterococci in both catheter types. However, Pseudomonas and Candida were more prevalent in cultures from indwelling catheters.
Bacteriuria in long-term catheterized patients is usually polymicrobial and, in addition to the pathogens commonly seen in short-term catheterized patients, commonly includes less familiar species such as P. mirabilis, Providencia spp., and Morganella morganii. In these patients, new episodes of infection often occur periodically in the presence of existing infection with organisms that may persist for months. A urine culture obtained from a patient whose catheter has a biofilm may not accurately reflect the status of bacteriuria in the bladder, and it is recommended that urine cultures from chronically catheterized patients be obtained from a freshly placed catheter.
Pathogenesis
In noncatheterized patients the usual origin of uropathogens is their own fecal microflora, which colonize the periurethral area and ascend to the bladder, resulting in bacteriuria with or without symptoms. In the mouse model of UTI, inoculation of E. coli into the bladder is followed by invasion of the superficial bladder cells and the formation of large intracellular bacterial colonies that, in response to infection, exfoliate and are removed with the flow of urine. To avoid clearance by exfoliation, these intracellular uropathogens can reemerge and eventually establish a persistent, quiescent bacterial reservoir within the bladder mucosa that may serve as a source for recurrent acute infections. Although internalization of uropathogenic E. coli into bladder and renal epithelial cells has been observed in vitro and in vivo, there is only sparse evidence that this phenomenon occurs in humans and only indirect evidence that the intracellular bacterial colonies observed in the mouse occur in humans. Specifically, intracellular bacterial clusters have been seen in desquamated bladder epithelial cells shed from children and adults with UTIs. It is possible that invasion of uropathogens into uroepithelial cells is the trigger for urinary symptoms, but an inflammatory response is not sufficient to cause urinary symptoms because pyuria often accompanies ASB in both catheterized and noncatheterized patients.
Strains of E. coli associated with lower or upper tract UTI in healthy hosts are more likely to have certain putative virulence determinants, such as P fimbriae, compared with colonic strains and those causing ASB. However, many UTIs are caused by E. coli with a virulence profile similar to that in strains causing ASB, and these putative virulence factors can be found in strains causing ASB or in colonic flora.
The most important predisposing factor for nosocomial UTI is urinary catheterization, which perturbs host defense mechanisms and provides easier access of uropathogens to the bladder. The indwelling urethral catheter introduces an inoculum of bacteria into the bladder at the time of insertion; facilitates ascension of uropathogens from the meatus to the bladder via the catheter-mucosa interface; provides a pool of organisms in the drainage bag, if the closed system is not maintained, which can ascend intraluminally to the bladder; compromises complete voiding; and constitutes a frequently manipulated foreign body on which pathogens are deposited via the hands of personnel. Indwelling urinary catheters provide a surface for the attachment of host cell binding receptors that are recognized by bacterial adhesins, thus enhancing microbial adhesion, as well as disrupting the uroepithelial mucosa to expose new binding sites for bacterial adhesins. Bacteria attached to the catheter surface form exopolysaccharides that entrap bacteria, which replicate and form microcolonies that mature into biofilms on the inner and outer surfaces of the catheter. These biofilms protect uropathogens from antimicrobials and the host immune response and facilitate transfer of antimicrobial resistance genes. Some uropathogens in biofilms, such as Proteus spp., have the ability to hydrolyze urea to free ammonia and raise the urinary pH, which facilitates precipitation of minerals such as hydroxyapatite or struvite, creating encrustations that can block catheter flow.
Whether external (condom) catheters also contribute to an increased risk of health care–associated UTI is unclear, because NHSN surveillance omits catheter types other than indwelling, transurethral catheters. A single center study in both acute and long-term care wards of 1009 sequential positive urine cultures collected from male veterans with either an indwelling (transurethral), external, suprapubic, or intermittent urinary catheter found that external catheters accounted for 37.4% of positive cultures. Indwelling catheters accounted for 57.8% of these cultures, and the other two catheter types combined accounted for the remaining 4.9%.
The source of uropathogens in catheterized patients includes patients’ endogenous flora, health care personnel, or inanimate objects. Not unexpectedly, uropathogen virulence determinants such as P fimbriae appear to be of much less importance in the pathogenesis of health care–associated UTIs compared with uncomplicated UTIs. Microbial pathogens can enter the catheterized bladder extraluminally (ascending outside the catheter along the urethral mucosa interface) or intraluminally (through the internal lumen from a contaminated drainage bag or break in the closed drainage system). Rectal and periurethral colonization with the infecting strain often precedes catheter-associated bacteriuria, especially in women. The negative impact of the catheter is demonstrated by the finding that, despite the continuous drainage of urine through the catheter, in patients with catheter urine colony counts as low as 3 to 4 colony-forming units per milliliter (CFU/mL) who are not given antimicrobials, the level of bacteriuria or candiduria uniformly rises to greater than 10 5 CFU/mL within 24 to 48 hours in those who remain catheterized.
Diagnosis
The clinical diagnosis of CAUTI is based on the presence of significant bacteriuria in a catheterized or recently catheterized person who has signs or symptoms of UTI not explainable by another condition after a thorough evaluation. Bacteriuria, urinary signs and symptoms, and pyuria in a catheterized patient are all nonspecific, and thus the clinician must exercise clinical judgment as to whether treatment is warranted. The latest NSHN definition (from January 2019) does not permit attribution of symptoms such as fever to another cause—if the patient has a urinary catheter and a positive urine culture that meets NHSN criteria for a CAUTI on the same day as the fever, a CAUTI must be reported. Mixed bacterial cultures and funguria in the absence of a bacterial organism do not meet the NHSN CAUTI definition.
Significant Bacteriuria
Significant bacteriuria is the level of bacteriuria that suggests bladder bacteriuria rather than contamination and is based on growth from a urine specimen collected in a manner to minimize contamination and transported to the laboratory in a timely fashion to limit bacterial growth. Definitions for significant bacteriuria are summarized in Table 302.3 . The preferred method of obtaining a urine culture in patients with short-term catheterization is by sampling through a needleless catheter port in catheter tubing that is well cleaned with a disinfectant before accessing. If a port is not present, puncturing the catheter tubing with a needle and syringe is satisfactory. In those patients with long-term indwelling catheters, the catheter urine may be unreliable, so a urine specimen should be obtained from a freshly placed catheter. Cultures should not be obtained from the drainage bag. Although data are lacking, placing a fresh condom catheter prior to urine specimen collection makes intrinsic sense.
TABLE 302.3
Definitions for Significant Bacteriuria a
| Noncatheterized, Clean-Catch Voided Specimen |
| Symptomatic Female or Male |
| ≥10 3 CFU/mL (based on data with coliforms; sparse data on gram-positive organisms) |
| Asymptomatic |
| Female: ≥10 5 CFU/mL of same species in two consecutive voided specimens |
| Male: ≥10 5 CFU/mL in single voided specimen |
| Catheterized: Urine From Freshly Placed Catheter Preferable |
| Symptomatic Female or Male |
| ≥10 3 CFU/mL |
| Asymptomatic Female or Male |
| ≥10 5 CFU/mL |
The level of bacteriuria considered significant in an asymptomatic noncatheterized woman is derived from studies in which colony counts in voided urine specimens were compared with paired catheter or suprapubic aspirate specimens. In these studies, a bacterial count of 10 5 CFU/mL or greater in a catheterized specimen was confirmed by a repeat catheterized specimen in more than 95% of cases. On the other hand, 10 5 CFU/mL or greater in a voided urine specimen was confirmed in a second voided specimen in only 80% of cases. However, two consecutive positive voided urine cultures predicted a third positive voided urine culture with 95% confidence. Therefore two consecutive voided specimens with 10 5 CFU/mL or greater of the same uropathogen predict bladder bacteriuria with the same degree of accuracy as a single urine specimen obtained through a catheter. Nevertheless, for practical purposes and cost containment, a single urine specimen with 10 5 CFU/mL or greater is often used to define significant bacteriuria in clinical practice and many studies. The finding of a single voided urine specimen with 10 5 CFU/mL or greater of an Enterobacteriaceae was reproducible in 98% of asymptomatic ambulatory noncatheterized men when the culture was repeated within 1 week. Thus a single, clean-catch voided urine specimen with 10 5 CFU/mL or greater of a uropathogen identifies ASB in men. Based on a comparison of voided urine specimens (from freshly applied condom catheters) and paired urethral catheter specimens, 10 5 CFU/mL or greater is also the appropriate quantitative criterion for ASB in a man with a condom catheter.
In symptomatic, noncatheterized men and women, lower colony counts of coliforms (e.g., E. coli, K. pneumoniae ) have been shown to be significant. A recent study of 236 symptomatic episodes of acute, uncomplicated cystitis in 226 women confirmed that the presence of even 10 2 E. coli in a midstream urine specimen was highly predictive of bladder bacteriuria (as determined by in-and-out catheterization). This study also found that enterococci and group B streptococci growing in voided urine generally were not found in the bladder urine, suggesting that they were usually contaminants—in fact, when these organisms were found in the midstream urine specimen, E. coli was present in the bladder urine in 61% of these episodes. In men with urinary symptoms, a quantitative count of 10 3 CFU/mL or greater in a voided specimen best defines UTI.
In urine specimens obtained by urethral catheterization from symptomatic or asymptomatic men and women, periurethral contamination is less of a problem, and lower quantitative counts of 10 2 CFU/mL or greater are considered to be significant in both men and women. However, most clinical laboratories do not routinely quantify urine cultures to 10 2 CFU/mL, so it is reasonable to use a quantitative count of 10 3 CFU/mL or greater in a symptomatic person, whether catheterized or not, as an indicator of CAUTI, because this threshold is a reasonable compromise between sensitivity in detecting bladder bacteriuria and feasibility for the microbiology laboratory in quantifying organisms. Of note, the level of bacteriuria or candiduria rapidly increases from small quantities to greater than 10 5 CFU/mL in catheterized individuals. In asymptomatic men and women, a colony count of 10 5 CFU/mL or greater is a reasonable criterion for the diagnosis of ASB, even though lower counts probably represent true bladder bacteriuria in catheter specimens, because increased specificity is desirable.
Symptoms and Signs
The majority of patients with catheter-associated bacteriuria lack symptoms, as demonstrated in a study of 1497 newly catheterized patients who were followed prospectively with daily urine cultures, urine leukocyte counts, and symptom assessment. Only 8% of 194 patients with catheter-associated bacteriuria (defined as >10 3 CFU/mL; 85% of patients had >10 5 CFU/mL in at least one culture) who could respond to symptom assessment reported symptoms referable to the urinary tract, although bacteriuria and pyuria had been present in most for many days. Additionally, there were no significant differences between patients with and without bacteriuria in signs or symptoms commonly associated with UTI—fever, dysuria, urgency, or flank pain—or in leukocytosis. The lack of an association between fever and catheter-associated bacteriuria has also been convincingly demonstrated in other studies. An ICU study found no relationship between fever and a UTI (defined as ≥10 5 CFU/mL of urine). Thus in the presence of an indwelling urinary catheter, symptoms referable to the urinary tract are unreliable, and fever or peripheral leukocytosis have little predictive value for the diagnosis of CAUTI. Likewise, no studies have demonstrated that malodorous or cloudy urine in a catheterized individual has clinical significance.
Nevertheless, catheterized patients with symptoms or signs compatible with UTI that are not explainable by another condition after a thorough evaluation warrant treatment. Signs and symptoms compatible with CAUTI are listed in Table 302.4 . Patients with CAUTI who are currently catheterized usually do not manifest the classic symptoms of dysuria, frequency, and urgency.
TABLE 302.4
Signs and Symptoms Compatible With Catheter-Associated Urinary Tract Infection (CAUTI)
| For all symptoms attributed to CAUTI, other causes should be considered and ruled out: |
| New onset or worsening of fever Altered mental status Flank pain Costovertebral angle tenderness Rigors Pelvic discomfort Malaise or lethargy Suprapubic pain or tenderness Dysuria a Urgent or frequent urination a |
| Patients with spinal cord injury may, in addition, demonstrate the following: |
| Increased spasticity Autonomic dysreflexia Sense of unease |
Noncatheterized adult residents of LTCFs are also at risk for health care–associated UTI. Most available evidence about what constitutes symptoms and signs of UTI in nursing home residents is from studies performed in women. Symptoms in older women that should prompt further urinary testing are fever, acute dysuria (<1 week in duration), new or worsening urinary urgency, frequency, new urinary incontinence, gross hematuria, suprapubic pain or tenderness, and costovertebral angle pain or tenderness. In a patient with cognitive impairment who is unable to express symptoms, a persistent change in mental status plus change in character of the urine that is not responsive to other interventions (i.e., hydration) may suggest a need for urine testing, among other evaluations.
Pyuria
Pyuria is evidence of inflammation in the genitourinary tract and is present in almost all persons with symptomatic UTIs. It is also common in persons with ASB, including 30% to 75% of bacteriuric patients with short-term indwelling urethral catheters and 50% to 100% of individuals with long-term indwelling catheters. In 761 newly catheterized patients in a university hospital, the specificity of pyuria for catheter-associated bacteriuria (>10 5 CFU/mL—almost all were asymptomatic) was 90%, but the sensitivity was only 47%. In a longitudinal study of patients with long-term urinary catheters, bacteriuria and pyuria were common, even during asymptomatic periods, and did not change during symptomatic UTI episodes. Thus in the catheterized patient, the presence or absence or degree of pyuria alone does not, by itself, differentiate catheter-associated ASB from CAUTI, but in a symptomatic patient its absence suggests that CAUTI is not the cause of the symptoms.
Prevention
Prevention of symptomatic CAUTI is the main objective of prevention strategies in patients for whom urinary catheterization is being considered or has been performed. However, there may also be benefits to preventing catheter-associated ASB in such patients, although such benefits have usually not been evaluated as end points in clinical trials. In the discussion that follows, the impact of interventions on catheter-associated ASB and CAUTI are mentioned when data are available, but most studies use catheter-associated bacteriuria (composed mostly of ASB) as the outcome of interest. Of note, interventions that reduce the risk of catheter-associated ASB are likely to also reduce the risk of CAUTI.
The following text discusses in detail those practices for which published data suggest that they should be implemented, those for which there are some positive data but not enough to warrant routine implementation, and those that do not warrant routine implementation on the basis of interpretation of currently available data. Prevention of one of the most significant harms of catheter-associated bacteriuria, inappropriate antimicrobial use to treat ASB, is addressed under “Health Care–Associated Asymptomatic Bacteriuria” later.
Prevention Strategies That Should Be Routine
Prevention Components of Infection Control Programs
Intensive infection surveillance and control programs in US hospitals are strongly associated with reductions in rates of nosocomial UTI. The decision in 2008 by the Centers for Medicare and Medicaid Services to stop reimbursing US hospitals for CAUTIs that develop during hospitalization has made CAUTI reduction a key component of many quality improvement programs, both state-wide and nationwide. Several evidence-based comprehensive guidelines have been published for prevention of CAUTIs, with an emphasis on infection prevention in hospitals. CAUTI prevention strategies that are strongly recommended for hospitals to incorporate into their infection control programs are shown in Table 302.5 . UTI bundles that combine several prevention techniques to accomplish reduction in CAUTI have been described.
TABLE 302.5
Catheter-Associated Urinary Tract Infection (CAUTI) Prevention and Monitoring Strategies Strongly Recommended for Acute-Care Hospitals
Modified from Yokoe DS, Anderson DJ, Berenholtz SM, et al. A compendium of strategies to prevent healthcare-associated infections in acute care hospitals: 2014 updates. Infect Control Hosp Epidemiol . 2014;35 Suppl 2:S21–31.
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NHSN, National Healthcare Safety Network.
It should be noted that our ability to prevent catheter-associated ASB or CAUTI in patients who have appropriate indications for catheterization is quite limited, especially in those patients requiring long-term bladder drainage. Many of the key evidence-based prevention strategies are being used more widely, although significant gaps in implementation exist. A national study of US hospitals in 2009 to ascertain the practices used to prevent CAUTI showed that although 79% of hospitals performed CAUTI surveillance, only 39% monitored duration or catheter removal or both. Another survey in 2009 in acute-care hospitals that participate in a geriatric nursing quality program showed that only 89% of respondents routinely wash hands before urinary catheter placement. In contrast, a survey in acute-care hospitals in 2013 found significant increases from 2005 to 2013 in use of catheter stop orders, use of bladder ultrasound to assess for urinary retention, and facility-wide monitoring of CAUTI rates ( P ≤ .001 for all comparisons).
Interestingly, a study of 398 health systems found no evidence that the 2008 Centers for Medicare and Medicaid Services policy to reduce payments for CAUTI has had any measurable effect on infection rates in US hospitals from 2006 to 2011 (incidence-rate ratio [IRR] in the postimplementation vs. preimplementation period, 1.03; P = .08). These findings align with those of the CDC summary report of NHSN surveillance in acute-care hospitals, which likewise found no change overall in CAUTI from 2009 to 2014.
Residents of LTCFs have a risk of developing health care–associated infections similar to that in acute-care hospital patients, and in the United States almost as many such infections occur annually in LTCFs as in hospitals. To address this problem, guidelines for infection prevention and control in LTCFs have been published. There has been less research on the efficacy of infection control strategies in LTCFs compared with hospitals, but guidelines for prevention of CAUTIs in hospitalized patients are thought to be generally applicable to catheterized residents in LTCFs. A systematic review of strategies to reduce CAUTI in nursing home residents found a variety of effective interventions, often implemented in bundles, including strategies to minimize catheter use, strategies to improve catheter care, and also general infection prevention strategies (such as hand hygiene). NHSN surveillance for health care–associated infections, including CAUTI, is currently optional for LTCFs.
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