Catheter Associated Urinary Tract Infections

As biofilm ultimately develops on all of these devices, the major determinant for development of bacteriuria is duration of catheterization. While the proportion of bacteriuric subjects who develop symptomatic infection is low, the high frequency of use of indwelling urinary catheters means there is a substantial burden attributable to these infections. Catheter-acquired urinary infection is the source for about 20% of episodes of health-care acquired bacteremia in acute care facilities, and over 50% in long term care facilities. The most important interventions to prevent bacteriuria and infection are to limit indwelling catheter use and, when catheter use is necessary, to discontinue the catheter as soon as clinically feasible. Infection control programs in health care facilities must implement and monitor strategies to limit catheter-acquired urinary infection, including surveillance of catheter use, appropriateness of catheter indications, and complications. Ultimately, prevention of these infections will require technical advances in catheter materials which prevent biofilm formation.

Indwelling urinary catheters are generally considered to be short term if they are in situ for less than 30 days and chronic or long term when in situ for 30 days or more. Indwelling catheter use in acute care facilities is usually short term, while chronic catheters are most common for residents of long term care facilities. Clinical and microbiologic considerations may vary for short and long term catheters. Urinary catheter acquired infection is usually manifested as asymptomatic bacteriuria (CA-ASB). The term catheter associated urinary tract infection (CA-UTI) is used to refer to individuals with symptomatic infection.

Pathogenesis of infection

Biofilm

Biofilm formation along the catheter surface is the most important cause of bacteriuria. Biofilm is a complex organic material consisting of micro-organisms growing in colonies within an extra-cellular mucopolysaccharide substance which they produce. Urine components, including Tamm-Horsfall protein and magnesium and calcium ions, are incorporated into this material. Biofilm formation begins immediately after catheter insertion, when organisms adhere to a conditioning film of host proteins which forms along the catheter surface. Both the interior and exterior catheter surfaces are involved. Bacteria usually originate from the periurethral area or ascend the drainage tubing following colonization of the drainage bag. Only about 5% of episodes of CA-ASB follow introduction of periurethral organisms into the bladder at the time of catheter insertion.

Organisms growing in the biofilm are in an environment where they are relatively protected from antimicrobials and host defenses. A single species is usually identified with the initial episode of bacteriuria following insertion of an indwelling catheter. If the catheter remains in situ and a mature biofilm develops, polymicrobial bacteriuria becomes the norm. For individuals with long term indwelling catheters, 3–5 organisms are usually isolated. The microbiology of biofilm on an indwelling catheter is dynamic with continuing turnover of organisms in the biofilm while the catheter remains in situ. Patients continue to acquire new organisms at a rate of about 3–7%/day.

Diagnosis of CA-UTI

Microbiologic diagnosis

Urine specimens for culture should be collected directly from the catheter or tubing, to maintain a closed drainage system. These may be collected either through the catheter collection port or through puncture of the tubing with a needle. CA-ASB is diagnosed when one or more organisms are present at quantitative counts ≥105 cful/ml from an appropriately collected urine specimen in a patient with no symptoms attributable to urinary infection. Lower quantitative counts may be isolated from urine specimens prior to ≥105 cfu/ml being present, but these lower counts likely reflect the presence of organisms in biofilm forming along the catheter, rather than bladder bacteriuria. A mature biofilm has usually formed once the catheter has been in situ for longer than 2 weeks. Urine collected through these catheters are contaminated by organisms present in the biofilm. There is a greater number of species and quantity of organisms isolated than these specimens compared with bladder urine collected simultaneously. Thus, it is recommended that the catheter be removed and a new catheter inserted, with specimen collection from the freshly placed catheter, before antimicrobial therapy is initiated for symptomatic infection. Organisms isolated with quantitative counts <105 cfu/ml from the replacement catheter tend not to persist.

Clinical diagnosis

The diagnosis of symptomatic CA-UTI is often a diagnosis of exclusion. Fever without localizing findings is the usual presentation of CA-UTI. Localizing signs or symptoms such as catheter obstruction, acute hematuria, recent trauma, suprapubic pain, or costovertebral angle pain or tenderness are helpful to identify a urinary source of fever, but are present in only a minority of episodes of presumed symptomatic infection. If localizing genitourinary findings are not present, fever in bacteriuric patients should be attributed to urinary infection only when there are no other potential sources. When the same organism is isolated from both the urine and a simultaneous blood culture, a diagnosis of CA-UTI is presumed in the absence of an alternate source for the bacteremia.

Pyuria

Bacteriuric patients usually have pyuria, irrespective of symptoms. Patients with an indwelling catheter may also have pyuria without bacteriuria, as the catheter itself may cause bladder inflammation. Other potential non-infectious causes of pyuria include renal disease, such as interstitial nephritis. Thus, the presence of pyuria in urine specimens obtained from a patient with an indwelling urinary catheter does not identify symptomatic infection in a bacteriuric subject, nor is it an indication for antimicrobial therapy.

The determinants of CA-UTI are not well described. However, catheter trauma or catheter obstruction are well recognized precipitating events. Risk factors for bloodstream infection from a urinary source in acute care patients are reported to be neutropenia, renal disease and male sex. Bacteremia is not a significant complication of chronic indwelling catheter replacement.


The complete original article and references by Lindsay E Nicolle may be found Antimicrobial Resistance and Infection Control Journal website, in the article "Catheter Associated Urinary Tract Infections"