on 24-Sep-2023 (Sun)

75% of UTIs acquired in the hospital are associated with urinary catheters

The incidence of bacteriuria associated with indwelling urethral catheterization with a closed drainage system is approximately 3% to 8% per day.

Catheter-associated bacteriuria is caused by a broad range of bacteria, including Escherichia coli, Pseudomonas aeruginosa, Klebsiella spp., and Enterococcus spp

Significant bacteriuria: ≥103 colony-forming units per milliliter (CFU/mL) in a symptomatic person is an indicator of CAUTI, whereas ≥105 CFU/mL in an asymptomatic person is an indicator of ASB

The majority of patients with catheter-associated bacteriuria are asymptomatic, and signs and symptoms commonly associated with UTI, such as fever, dysuria, urgency, flank pain, or leukocytosis, are either nonspecific or not apparent in catheterized patients

In the catheterized patient, pyuria does not differentiate ASB from CAUTI, but its absence suggests that CAUTI is not the cause of symptoms

Routine screening for and treatment of ASB in health care settings is discouraged, other than for pregnant women and patients undergoing urologic procedures that cause mucosal bleeding

Urine cultures should be obtained before treatment of CAUTI, ideally after catheter change

Recommended treatment duration for CAUTI ranges from 5 to 14 days, depending on the severity and choice of drug

All types of urinary catheters (indwelling, suprapubic, intermittent, and external or condom catheters) increase the risk of acquisition of bacteriuria and thus UTI.

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).2

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,3,4 although this latter point is controversial.

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

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.6,7 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,9 and at this point it is not possible to predict which patients with bacteriuria will develop bacteremia.

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.

In one study of 1453 health care–associated, symptomatic UTIs, 72% were CAUTIs and 28% were not catheter associ- ated.10 Almost half of the CAUTIs (45%) occurred among intensive care unit (ICU) patients.

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.

Common indications for urinary catheter use in acute care are discussed later under “Reduction of Unnecessary Catheterization” (see Table 30 2.6 ). Most of these patients are catheterized for only 2 to 4 days.14

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.15

The incidence of bacteriuria associated with indwelling urethral catheterization with a closed drainage system is approximately 3% to 8% per day16–18 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,14 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.13

Organisms causing CAUTI and reported to the NSHN are often resistant, with Escherichia coli fluoroquinolone resistance reported at 34.8% in 2014.19

The duration of catheterization is the most important risk factor for the development of catheter-associated bacteriuria.14,20,21 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.16,21–23

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.25–28

In one study of 235 new cases of catheter-associated bacteriuria, more than 90% of the patients were asymptomatic and afebrile.28

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.29

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.30

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.31 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.28

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.32

Risk factors for urinary catheter– associated bacteremia include male sex, immunosuppression, and urinary tract procedures.33

Urinary tract organisms are also the most common source of bacteremia in LTCFs, accounting for 40% to 55% of bactere- mias,34,35 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.14

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 confound- ing variables probably explains some of the association, because patients who require an indwelling catheter tend to be sicker or have comorbidi- ties.

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.41 Of those treated inappropriately, 14% received over 14 days of antimicrobials. Inappropri- ate treatment is associated with older age, predominantly gram-negative bacteriuria, and pyuria.41,42

Inappropriate antimicrobial use also unneces- sarily exacerbates the growing problem of health care–associated C. difficile colitis,43 by 8.5-fold in a study of ASB treatment in nursing homes.44

Most episodes of bacteriuria in short-term catheterized patients are caused by single organisms, mostly gram-negative bacilli and enterococci.28

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%).

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.

Bacteriuria in long-term catheterized patients is usually polymicrobial and, in addition to the pathogens commonly seen in short-term catheter- ized patients, commonly includes less familiar species such as P. mirabilis, Providencia spp., and Morganella morganii.40

A urine culture obtained from a patient whose catheter has a biofilm may not accurately reflect the status of bacteriuria in the bladder,53,54 and it is recommended that urine cultures from chronically catheterized patients be obtained from a freshly placed catheter

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

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 organ- isms 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.

acteria 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.22,56 These biofilms protect uropathogens from antimicrobials and the host immune response and facilitate transfer of antimicrobial resistance genes.56

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.22,56

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.63 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.22,45,64,65

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.61,62,66

Rectal and periurethral colonization with the infecting strain often precedes catheter-associated bacteriuria, especially in women.65

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 105 CFU/mL within 24 to 48 hours in those who remain catheterized.68

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.

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

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.40

In those patients with long-term indwelling catheters, the catheter urine may be unreliable,53,54 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

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.69 In these studies, a bacterial count of 105 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, 105 CFU/mL or greater in a voided urine specimen was confirmed in a second voided specimen in only 80% of cases. However, two consecu- tive positive voided urine cultures predicted a third positive voided urine culture with 95% confidence.

Nevertheless, for practical purposes and cost containment, a single urine specimen with 105 CFU/mL or greater is often used to define significant bacteriuria in clinical practice and many studies.5

The finding of a single voided urine specimen with 105 CFU/mL or greater of an Enterobacteriaceae was reproducible in 98% of asymptomatic ambulatory noncatheterized men when the culture was repeated within 1 week.70 Thus a single, clean-catch voided urine specimen with 105 CFU/mL or greater of a uropathogen identifies ASB in men.5

Based on a comparison of voided urine specimens (from freshly applied condom catheters) and paired urethral catheter specimens, 105 CFU/mL or greater is also the appropriate quantitative criterion for ASB in a man with a condom catheter.71

A recent study of 236 symptomatic episodes of acute, uncomplicated cystitis in 226 women confirmed that the presence of even 102 E. coli in a midstream urine specimen was highly predictive of bladder bacteriuria (as determined by in-and-out catheterization).73 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 103 CFU/mL or greater in a voided specimen best defines UTI.74

In urine specimens obtained by urethral catheterization from symptomatic or asymptomatic men and women, periurethral contamina- tion is less of a problem, and lower quantitative counts of 102 CFU/mL or greater are considered to be significant in both men and women.5,75 However, most clinical laboratories do not routinely quantify urine cultures to 102 CFU/mL, so it is reasonable to use a quantitative count of 103 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 105 CFU/mL in catheterized individuals.68 In asymptomatic men and women, a colony count of 105 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

Only 8% of 194 patients with catheter-associated bacteriuria (defined as >103 CFU/ mL; 85% of patients had >105 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.29,39 An ICU study found no relationship between fever and a UTI (defined as ≥105 CFU/mL of urine).76 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 Tab le 3 02 .4 . Patients with CAUTI who are currently catheterized usually do not manifest the classic symptoms of dysuria, frequency, and urgency.

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 (<7

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 interven- tions (i.e., hydration) may suggest a need for urine testing, among other evaluations.77