Catheter-associated urinary tract infection in adults

INTRODUCTION — Urinary catheters are placed for a number of reasons, including diagnostic and therapeutic reasons, as well as for convenience. The presence of a catheter increases the risk of bacteriuria, which can be clinically benign or progress to serious infection. There is an overall lack of consensus about the optimal approach to catheter-associated urinary tract infections (UTIs), apart from removing catheters when no longer necessary.

Issues related to symptomatic UTI and asymptomatic bacteriuria in patients with indwelling bladder catheters will be reviewed in this topic.

Issues related to asymptomatic bacteriuria and cystitis in other circumstances, and the indications for placement, methods of catheterization, and management and complications of bladder catheters are discussed separately. (See "Asymptomatic bacteriuria in adults" and "Acute simple cystitis in adult and adolescent females" and "Acute simple cystitis in adult and adolescent males" and "Placement and management of urinary bladder catheters in adults" and "Complications of urinary bladder catheters and preventive strategies" and "Acute complicated urinary tract infection (including pyelonephritis) in adults and adolescents".)

DEFINITIONS — Because the presence of bacteria in a urine sample may represent contamination by bacteria colonizing the periurethral area in addition to bladder bacteriuria, thresholds for bacterial growth from a urine sample that is likely to represent true bladder bacteriuria in specific contexts have been suggested by various expert groups. The Infectious Diseases Society of America (IDSA) guidelines define catheter-associated bacteriuria as follows [1]:

●Symptomatic bacteriuria (urinary tract infection [UTI]) – Culture growth of ≥10³ colony forming units (cfu)/mL of uropathogenic bacteria in the presence of symptoms or signs compatible with UTI without other identifiable source in a patient with indwelling urethral, indwelling suprapubic, or intermittent catheterization. Compatible symptoms include fever, suprapubic or costovertebral angle tenderness, and otherwise unexplained systemic symptoms such as altered mental status, hypotension, or evidence of a systemic inflammatory response syndrome.

●Asymptomatic bacteriuria – Culture growth of ≥10⁵ cfu/mL of uropathogenic bacteria in the absence of symptoms compatible with UTI in a patient with indwelling urethral, indwelling suprapubic, or intermittent catheterization.

Patients who are no longer catheterized but had urethral, suprapubic, or condom catheters within the past 48 hours are also considered to have catheter-associated UTI or asymptomatic bacteriuria if they meet these definitions.

Because periurethral contamination is less likely in catheterized specimens, a relatively low threshold for bacteria growth in a symptomatic patient is likely to represent true bladder bacteriuria. Although the IDSA guidelines acknowledge that growth as low as 10² cfu/mL has been associated with bladder bacteriuria in the setting of symptoms, the threshold of 10³ cfu/mL was chosen since many labs do not quantify growth below that threshold.

In contrast, use of a higher threshold in asymptomatic patients is reasonable given the low rate of complications is this setting and the desire for increased specificity to reduce the overuse of antimicrobials, even if bacterial growth does represent bladder bacteriuria. (See 'Asymptomatic bacteriuria' below.)

These definitions are different from those used by the United States Centers for Disease Control and Prevention (CDC) National Health Safety Network (NHSN), which were created for surveillance purposes, not specifically for clinical care [2]. The NHSN uses the same basic definition for asymptomatic bacteriuria but defines catheter-associated UTI as the presence of fever, suprapubic tenderness, or costovertebral angle pain in the setting of urine culture with bacterial counts ≥10⁵ cfu/mL of no more than two organism species (and does not include fungal isolates or minor pathogens). The NHSN definition does not allow for other attribution of fever, so it may overestimate the rate of clinically relevant catheter-related bacteriuria [3]. Furthermore, because the NHSN definition sometimes changes, it can be difficult to compare infection rates across time. As an example, one hospital-based study noted that the measured infection rate as determined retroactively by the updated definition fell by half compared with the rate reported using the old definition [4].

The NHSN definitions also make attempts to distinguish between hospital-acquired and pre-existing UTIs in order to allow attribution to the institution where the urine was collected or to another facility.

EPIDEMIOLOGY

Incidence — Bacteriuria in patients with indwelling bladder catheters occurs at a rate of approximately 3 to 10 percent per day of catheterization [5,6]. Of those with bacteriuria, 10 to 25 percent develop symptoms of urinary tract infection (UTI) [7-9].

This translates into a substantial burden of catheter-associated UTIs in hospitalized patients. In the United States, based on surveillance data reported to the CDC National Healthcare Safety Network, the incidence of catheter-associated UTIs in 2012 was 1.4 to 1.7 per 1,000 catheter days in inpatient adult and pediatric medical/surgical floors [10].

Risk factors — The duration of catheterization is an important risk factor for catheter-associated bacteriuria and UTI and is a major target of prevention efforts [11,12]. (See 'Prevention' below.)

Other risk factors include [13-15]:

●Female sex

●Older age

●Diabetes mellitus

●Bacterial colonization of the drainage bag

●Errors in catheter care (eg, errors in sterile technique, not maintaining a closed drainage system, etc.)

PATHOGENESIS — Urinary tract infection (UTI) associated with catheterization may be extraluminal or intraluminal. Extraluminal infection occurs via entry of bacteria into the bladder along the biofilm that forms around the catheter in the urethra [16-19]. Intraluminal infection occurs due to urinary stasis because of drainage failure, or due to contamination of the urine collection bag with subsequent ascending infection. Extraluminal is more common than intraluminal infection (66 versus 34 percent in one study) [20].

Rarely, there can be purple discoloration of the urine, collecting bag, and tubing (the purple urine bag syndrome) [21]. The purple color of the urine is due to metabolic products of biochemical reactions formed by bacterial enzymes in the urine. Gastrointestinal tract flora break down the amino acid tryptophan into indole, which is subsequently absorbed into the portal circulation and converted into indoxyl sulfate. Indoxyl sulfate is then excreted into the urine, where it can be broken down into indoxyl if the appropriate alkaline environment and bacterial enzymes (indoxyl sulfatase and indoxyl phosphatase) are present. The breakdown products, indigo and indirubin, appear blue and red, respectively [22,23]. Bacteria capable of producing these enzymes include Providencia spp, Klebsiella, and Proteus.

MICROBIOLOGY

Spectrum of organisms — The causative pathogens in catheter-associated urinary tract infection (UTI) and asymptomatic bacteriuria are similar to those that are associated with complicated UTI in general. Specifically, Escherichia coli and other Enterobacteriaceae are common, but Pseudomonas aeruginosa, enterococci, staphylococci, and fungi are also significant causes. (See "Acute complicated urinary tract infection (including pyelonephritis) in adults and adolescents", section on 'Microbiology'.)

As an example, of approximately 154,000 catheter-associated UTIs reported by acute care hospitals and long-term acute care facilities to the US National Healthcare Safety Network (NHSN) between 2011 and 2014, the most common causative pathogens identified were [24]:

●E. coli — present in 24 percent of cases

●Candida spp (or yeast, not otherwise specified) — 24 percent

●Enterococcus spp — 14 percent

●P. aeruginosa — 10 percent

●Klebsiella spp — 10 percent

Ambulatory patients with indwelling catheters tend to acquire urinary bacteria similar to those found in hospitalized patients rather than the types usually seen in the outpatient setting. Prolonged catheterization can be associated with polymicrobial bacteriuria or changing urinary flora.

Some of these organisms associated with catheter-related bacteriuria or funguria may lack some of the virulence factors that allow the usual uropathogens to adhere to uroepithelium, but they take advantage of easy access to the bladder via the catheter. A good example of such an organism is Candida spp, which almost never cause UTI in the absence of an indwelling catheter. In contrast, candiduria is a common finding in patients with indwelling bladder catheters, particularly in those who are taking antimicrobials or are diabetic [25]. However, most patients are asymptomatic, funguria merely represents colonization, and progression to candidemia is uncommon (1.3 percent in one series) [25]. This problem is discussed in detail separately. (See "Candida infections of the bladder and kidneys", section on 'Infection versus colonization'.)

Antimicrobial resistance — Organisms that cause catheter-associated UTI and asymptomatic bacteriuria are increasingly resistant to antimicrobial agents.

Of the 10,800 E. coli catheter-associated isolates reported to the US NHSN in 2014, 35 percent were resistant to fluoroquinolones, and 16 percent to advanced generation anti-pseudomonal cephalosporins (ie, cefepime and ceftazidime) [24]. Of 4700 Klebsiella isolates, 9.5 percent were resistant to carbapenems.

CLINICAL FEATURES

Symptoms and signs — Symptoms of catheter-associated urinary tract infection (UTI) are protean and do not necessarily refer to the urinary tract. Fever is the most common symptom [1,7,26]. Localizing symptoms may include flank or suprapubic discomfort, costovertebral angle tenderness, and catheter obstruction. However, many catheterized patients without evidence of UTI or even bacteriuria may have similar symptoms. As an example, in an observational study that included 89 hospitalized patients who developed bacteriuria following placement of a urethral catheter, 18 percent had a temperature >38.5 C (101.3 F), 6 percent had dysuria, and 6 percent had urinary urgency [7]. These symptoms were present in the same proportion of 945 catheterized patients without bacteriuria.

Patients with spinal cord injury may have especially atypical and nonspecific symptoms, including increased spasticity, malaise/lethargy, and autonomic dysreflexia. Individuals who develop UTI soon after removal of a catheter may be more likely to have the typical urinary symptoms of dysuria, frequency, and urgency.

Many patients believe that a cloudy appearance or foul smell of the urine is suggestive of the presence of a UTI. However, neither of these findings has been demonstrated to be clearly associated with either bacteriuria or a UTI [1,26].

Rarely, purple discoloration of the urine, collection bag, and tubing (purple urine bag syndrome [PUBS]) can occur due to metabolic byproducts of certain bacteria that may be present in the system [21]. Risk factors include bacteriuria, constipation, and female sex. PUBS is benign and has not been demonstrated to have any implication other than the possibility of a UTI. (See 'Pathogenesis' above.)

Laboratory findings — Pyuria is a common finding in catheterized patients with bacteriuria, whether they are symptomatic (ie, have UTI) or not. However, in a series of 761 catheterized patients, quantitative urine WBC >10 cells/microL had low sensitivity for predicting growth of >10⁵ colony forming units (cfu)/mL (47 percent) [27]. Specificity, on the other hand, was 90 percent. The vast majority of these patients had no symptoms attributable to UTI.

By definition, all patients with catheter-associated UTI have bacteriuria or funguria. The vast majority of patients with symptomatic bacteriuria (ie, UTI) have bacterial culture growth ≥10⁵ cfu/mL or fungal growth in urine, although occasionally bacterial counts as low as 10² cfu/mL have also been described in individuals with UTI in the absence of a catheter [28,29]. The frequency of low count bacteriuria in the setting of catheter-associated UTI is not clearly defined but expected to be very low [1,26]. The spectrum of associated pathogens is discussed elsewhere. (See 'Spectrum of organisms' above.)

DIAGNOSIS

General approach — The diagnosis of a catheter-associated UTI is made by the finding of bacteriuria in a catheterized patient who has signs and symptoms that are consistent with UTI or systemic infection that are otherwise unexplained. A UTI diagnosed in a patient who had a catheter removed within the past 48 hours is also considered a catheter-associated UTI. (See 'Definitions' above.)

Consistent findings may be specific to the urinary tract (eg, costovertebral angle tenderness) or may be more general, such as fever, leukocytosis, fall in blood pressure, metabolic acidosis, or respiratory alkalosis. If the diagnosis is based on such nonspecific findings, the evaluation should rule out the possibility of other infections (eg, bacteremia, pneumonia, skin or soft tissue infection) prior to attributing them to a catheter-associated UTI.

Because the symptoms and signs of catheter-associated UTI can be nonspecific, a fair amount of clinical judgment and individualization is required. Older or debilitated patients often present with nonspecific signs or symptoms, such as falls, change in functional status, and change in mental status. Because older catheterized patients often have bacteriuria, these findings have traditionally been attributed to UTI in such patients. However, growing evidence indicates that these are not reliable predictors of bacteriuria or UTI, and treatment for bacteriuria does not improve these symptoms [30-32]. Thus, we do not routinely test urine in such patients in the absence of focal urinary tract symptoms or systemic signs of infection (eg, fever), and instead hydrate, correct metabolic abnormalities, and assess other potential contributing factors. (See "Approach to infection in the older adult", section on 'Urinary tract infection'.)

The vast majority of patients with catheter-associated UTI have counts ≥10⁵ cfu/mL. Thus, when the level of bacteriuria is lower, other potential explanations for the presenting symptoms should be evaluated before diagnosing a catheter-associated UTI, particularly if the symptoms are nonspecific or the isolated organisms are not Enterobacteriaceae.

Certain findings, such as pyuria and the appearance or smell of the urine, should not be used to diagnose a UTI when found in isolation. Pyuria is frequently found in catheterized patients with bacteriuria, whether they have symptoms or not, and odorous or cloudy urine has not been demonstrated to be indicative of either bacteriuria or UTI. On the other hand, the absence of pyuria in a symptomatic catheterized patient suggests a diagnosis other than UTI. (See 'Clinical features' above.)

Specimen collection — Ideally urine samples for culture should be obtained by removing the indwelling catheter and obtaining a midstream specimen. If ongoing catheterization is needed, the catheter should be replaced prior to collecting a urine sample for culture, to avoid culturing bacteria present in the biofilm of the catheter but not in the bladder.

Many systems have a "needleless" site that can be cleansed prior to specimen collection. If a sample is being collected without catheter removal, urine should be obtained from the port in the drainage system (figure 1) [33]. For circumstances in which the above approaches are not possible, the culture should be obtained by separating the catheter from the drainage system. Although this approach is associated with some risk of introducing microbes into the closed system, culture results from urine collected from the drainage bag cannot be used to guide treatment.

In the setting of condom catheters, it can be difficult to distinguish true infection from skin and mucosal contamination [17,34]. In these cases, a clean catch midstream specimen should be obtained, or urine should be collected from a freshly applied condom catheter after cleaning the glans [34]. (See "Sampling and evaluation of voided urine in the diagnosis of urinary tract infection in adults".)

TREATMENT — The approach to treatment of catheter-associated urinary tract infection (UTI) includes antimicrobial therapy and catheter management.

Antimicrobial therapy — The approach to empiric antimicrobial therapy for patients with catheter-associated UTI depends in part on the presentation and whether there are features that suggest an infection that has extended beyond the bladder (which we use to distinguish acute complicated UTI from acute simple cystitis). Most patients with catheter-associated UTI come to clinical attention because of fever, flank pain, costovertebral angle tenderness, or systemic signs or symptoms of infection in the setting of pyuria and bacteriuria; such cases are consistent with acute complicated UTI and are managed as such. (See "Acute complicated urinary tract infection (including pyelonephritis) in adults and adolescents", section on 'Management'.)

Some patients, in particular those who have recently had catheter removal, present with isolated symptoms of cystitis (eg, dysuria, urinary frequency or urgency) in the absence of fever or features of ascending infection or prostatitis. Such patients can be managed as having acute simple cystitis. (See "Acute simple cystitis in adult and adolescent females" and "Acute simple cystitis in adult and adolescent males".)

Antibiotic selection for both acute complicated UTI and acute simple cystitis takes into account risk factors for resistant infection (informed by past urine cultures, use of antimicrobial therapy, health care exposures, community prevalence of antimicrobial resistance) and antibiotic allergies.

Once culture and susceptibility results are available, the antimicrobial regimen should be tailored to the specific organism isolated. The approach to management of Candida UTIs is discussed elsewhere. (See "Candida infections of the bladder and kidneys", section on 'Treatment'.)

The optimal duration of therapy is uncertain. Depending on the clinical response, the infecting organism, and the agent used for treatment, 7 to 10 days of therapy is generally appropriate (with longer therapy for patients who respond slowly) [1]. Oral therapy can be used for some or all of the treatment course if the organism is susceptible and the patient is well enough to take oral medication with adequate absorption.

Catheter management — The optimal approach to catheter management in the setting of urinary tract infection (UTI) is uncertain, although minimization of the use of indwelling catheters, when possible, is preferred. In general, patients who no longer require catheterization should have the catheter removed and receive appropriate antimicrobial therapy [35,36]. Patients who require extended catheterization should be managed with intermittent catheterization, if possible. (See "Placement and management of urinary bladder catheters in adults", section on 'Catheter removal' and "Placement and management of urinary bladder catheters in adults", section on 'Clean intermittent catheterization'.)

Intermittent catheterization is associated with a lower rate of bacteriuria and UTI than long term indwelling catheterization [37]. If long term catheterization is needed and intermittent catheterization is not feasible, the catheter should be replaced at the initiation of antimicrobial therapy [38]. Catheter replacement is associated with fewer and later relapses than retaining the original catheter, as biofilm penetration of most antimicrobials is poor [39].

COMPLICATIONS — Important complications of catheter-associated urinary tract infections (UTIs) include sepsis, bacteremia, and involvement of the upper urinary tract.

Approximately 20 percent of health care-associated bacteremias arise from the urinary tract, and the mortality associated with this condition is about 10 percent [40]. In the intensive care unit setting, a lower proportion of bacteremia is attributable to catheter-associated UTIs [1].

Upper tract infection is another important consequence of catheter associated urinary tract infection. In an autopsy series of 75 nursing home patients, the incidence of renal parenchymal inflammation was higher in those with a catheter in place at the time of death than in those who were not catheterized (38 versus 5 percent) [41]. The implications of this finding are not known.

ASYMPTOMATIC BACTERIURIA — Bacteriuria in the absence of symptoms is very common among catheterized patients [7]. Treatment of asymptomatic bacteriuria does not affect patient outcomes, including the risk of complications and or the subsequent development of UTI symptoms, and increases the likelihood of emergence of resistant bacteria [1,42,43]. Thus, with few exceptions, screening and treatment for asymptomatic bacteriuria in catheterized patients is not indicated. (See "Asymptomatic bacteriuria in adults", section on 'Rationale for not treating'.)

Evaluating for asymptomatic bacteriuria in patients with indwelling catheters is warranted only in the setting of pregnancy or prior to urologic procedures for which mucosal bleeding is anticipated because of very specific risks of bacteriuria in these particular populations. (See "Urinary tract infections and asymptomatic bacteriuria in pregnancy", section on 'Asymptomatic bacteriuria' and "Asymptomatic bacteriuria in adults", section on 'Patients undergoing urologic intervention'.)

PREVENTION — In general, the most important aspects of prevention of catheter-associated urinary tract infections (UTI) are avoidance of unnecessary catheterization, use of sterile technique when placing the catheter, and removal of the catheter as soon as possible. As an example, in a nationwide prospective study in the United States, implementing initiatives to reinforce these concepts was associated with a decline in the baseline rate of catheter-associated UTIs in non-intensive care units [44]. Similarly, in a Canadian study, there was a modest but sustained reduction in post-operative UTI with a standardized approach to perioperative bladder catheterization that followed these principles [45].

There is no clear benefit to using either antibiotic-coated urinary catheters or prophylactic antibiotics to reduce the risk of catheter associated urinary tract infection. These and other issues related to catheter care for prevention of UTI are discussed in detail separately. (See "Placement and management of urinary bladder catheters in adults", section on 'Catheter care' and "Placement and management of urinary bladder catheters in adults", section on 'To prevent urinary tract infection' and "Placement and management of urinary bladder catheters in adults", section on 'Catheter removal' and "Placement and management of urinary bladder catheters in adults", section on 'Prophylactic antibiotics'.)

RECOMMENDATIONS OF OTHERS — Several expert and governmental groups have released guidelines or recommendations on the identification, management, and prevention of catheter associated urinary tract infections (UTIs) [1,12,40,46]. All of them stress restricting the use of indwelling catheters and those that address treatment recommend avoidance of unnecessary antimicrobial use for asymptomatic bacteriuria.

The Infectious Diseases Society of America (IDSA), in collaboration with other international expert groups, released practice guidelines on the diagnosis, prevention, and treatment of catheter-associated UTI in 2009 [1]. The discussion in this topic is generally consistent with those guidelines.

In 2014, a collaborative panel sponsored by the Society for Healthcare Epidemiology of America (SHEA) released recommendations on the prevention of catheter-associated UTI [12]. This publication highlighted the importance of the judicious use of urethral catheters only for appropriate indications, adequate expertise and sterile technique for insertion, continued assessment of the necessity of catheterization, and maintenance of a sterile, continuously closed drainage system that allows unobstructed urine flow.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Urinary tract infections in adults".)

SUMMARY AND RECOMMENDATIONS

●Incidence and risk factors – Catheter-associated urinary tract infections (UTIs) are a common health care-associated infection. Bacteriuria in patients with indwelling bladder catheters occurs at a rate of approximately 3 to 10 percent per day of catheterization. Of those with bacteriuria, approximately 10 to 25 percent develop UTI. The most important risk factor is the duration of catheterization. Other risk factors include errors in catheter care. (See 'Epidemiology' above.)

●Clinical features – Fever is the most common symptom of catheter-associated UTI. Pyuria is usually present. Localizing symptoms may include flank or suprapubic discomfort, costovertebral angle tenderness, and catheter obstruction. However, these symptoms are not specific to UTI and may be seen in catheterized patients without bacteriuria. Pyuria is also common in catheterized patients with bacteriuria without UTI. (See 'Clinical features' above.)

●Diagnosis – The diagnosis of a catheter-associated UTI is made by the finding of bacteriuria in a catheterized patient who has signs and symptoms that are consistent with UTI or systemic infection and are otherwise unexplained. Consistent findings may be specific to the urinary tract or may be more general, such as fever, leukocytosis, or signs of sepsis. If the diagnosis is based on such nonspecific findings, the evaluation should rule out the possibility of other systemic infections (eg, bacteremia, pneumonia, skin or soft tissue infection) prior to attributing them to a catheter-associated UTI. (See 'Diagnosis' above.)

●Limited role for urine testing for isolated mental status changes – For older patients with an indwelling urinary catheter and a change in functional or mental status, we do not check urine studies or otherwise make the diagnosis of UTI in the absence of focal urinary tract symptoms or systemic signs of infection. (See 'General approach' above and "Approach to infection in the older adult", section on 'Urinary tract infection'.)

●Optimal specimen collection for culture – Ideally, urine samples for culture should be obtained by removing the indwelling catheter and obtaining a midstream specimen or, if ongoing catheterization is warranted, a specimen through a new catheter. When this is not possible, the culture should be obtained through the catheter port, not the drainage bag. (See 'Specimen collection' above.)

●Antimicrobial therapy – Antimicrobial selection should be based upon the culture results when available. However, in some cases, prompt treatment is warranted prior to the availability of culture data. In such cases, empiric antimicrobial choice should be tailored to results of past cultures, use of prior antimicrobial therapy, community prevalence of antimicrobial resistance, and antimicrobial allergies of the patient. Depending on the clinical response, the infecting organism, and the agent used for treatment, 7 to 10 days of therapy is generally appropriate. (See 'Antimicrobial therapy' above.)

●Catheter management – In general, patients with infection who no longer require catheterization should have the catheter removed and receive appropriate antimicrobial therapy. Patients who require extended catheterization should be managed with intermittent catheterization, if possible. If long term catheterization is needed and intermittent catheterization is not feasible, the catheter should be replaced at the initiation of antimicrobial therapy. (See 'Catheter management' above.)

●Avoid evaluating for and treating asymptomatic bacteriuria – Evaluating for asymptomatic bacteriuria in patients with indwelling catheters is warranted only in the setting of pregnancy or prior to urologic procedures for which mucosal bleeding is anticipated. For other asymptomatic patients with indwelling catheters, routine urine cultures and urinalyses are not warranted and treatment of incidentally discovered asymptomatic bacteriuria is not indicated. (See 'Asymptomatic bacteriuria' above.)

●Prevention – Avoidance of unnecessary catheterization, use of sterile technique for insertion, and removal as soon as possible are essential to the prevention of catheter-associated UTI. Antimicrobial agents have no role in prevention of infection for the majority of patients with urinary catheters. (See 'Prevention' above and "Placement and management of urinary bladder catheters in adults".)