Urinary Tract Infections Catheter-Associated

Authors: FME Wagenlehner, MD, PhD KG Naber, MD, PhD

Forty per cent of nosocomial infections originate in the urinary tract. The majority of patients have chronic indwelling catheters (80%). In the 1920s, Foley introduced the self-retaining catheter. However, initially it was used with open drainage, and bacteriuria was virtually universal by the end of the fourth day. With the introduction and development of plastics technology and the design of suitable receptacles, closed-catheter systems were introduced. Development of bacteriuria was delayed but still universal after 30 days. A control trial comparing open with closed catheters was never performed and quite soon it became clear that there was little point in stating the obvious and closed systems became the standard.

Risk of Bacteriuria

An indwelling catheter bypasses normal urethral host defenses, so allowing continuous access of organisms to the urinary tract. Multivariate analyses have emphasized that the duration of catheterization is the most important risk factor in the development of catheter-associated bacteriuria.

Other risk factors include the following:

(a) colonization of the drainage bag, catheter and periurethral segment

(b) diabetes mellitus

(c) female patient

(d) renal function impairment

(e) poor quality of catheter care.


The urethral catheter can inhibit or bypass some defense mechanisms which would normally prevent or minimize bacteria-epithelial cell interactions, e.g. GAG layer, biofilm formation. Bacteria can enter the urinary tract in catheterized patients through the following routes:

This may be a consequence of inadequate cleansing of the introitus, distal urethra and perineum. There is unlikely to be any consequence in otherwise healthy individuals. It would be responsible for the bacteriuria seen in patients on intermittent clean catheterization, where very little attempt is made to cleanse the ‘entry points’ before introduction of the catheter. It is doubtful whether such cleansing is of any significant benefit, but introduction of organisms at the time of catheterization could be critical in hospitalized patients. Up to 20% of individuals will be colonized immediately after catheterization.

At the Time of Catheter Insertion

This may be a consequence of inadequate cleansing of the introitus, distal urethra and perineum. There is unlikely to be any consequence in otherwise healthy individuals. It would be responsible for the bacteriuria seen in patients on intermittent clean catheterization, where very little attempt is made to cleanse the ‘entry points’ before introduction of the catheter. It is doubtful whether such cleansing is of any significant benefit, but introduction of organisms at the time of catheterization could be critical in hospitalized patients. Up to 20% of individuals will be colonized immediately after catheterization.

After Catheter Insertion

Long-term catheterization will promote the development of a mucous sheath developing loosely between the catheter and urethral mucosa. This provides a favorable environment for bacterial invasion and perforation.

Arguably, it is responsible for a greater proportion of bacteriuria in women (70-80%) than in men (20-30%).

In males the predominant route is through the lumen of the catheter and collecting system by retrograde spread, i.e. ascending infection against the flow of urine. The taps of the drainage bags commonly become contaminated and regular opening of these and the connecting points, which may become disconnected for the purposes of bladder washout or urine collection, will promote entry of bacteria into the system. Sterile pyuria is commonplace in patients with urinary catheters.

Biofilm Infection

Biofilm is an accumulation of micro-organisms and their nucleic acid fragments within a mucopolysaccharide medium, which together form a structured community on a solid surface. Biofilms are ubiquitous. In the context of urological practice they can be demonstrated on catheters, drainage bags and other foreign bodies and prostheses. They can also be found within renal scars at sites of chronic infection (e.g. prostatitis, epididymitis).

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Methods of Catheterization and Risk of UTI

Single Catheterization - ‘in-out’

Bacteriuria develops in 1-5% of patients. The risk is increased in females, patients with retention, peripartum catheterization, prostatic obstruction, diabetes mellitus, debilitation and the elderly.

Short-term Catheterization

Between 15% and 25% of patients admitted to hospital may be catheterized between 2 and 4 days during their stay. Between 10% and 30% will develop bacteriuria. Most episodes of short-term catheter-associated bacteriuria are asymptomatic and are caused by single organisms. Most catheter-associated bacteriurias are accompanied by pyuria.

Long-term Catheterization

Bacteriuria with at least one strain is universal, while most patients are infected with two or more strains. The commonest infecting organism is E. coli. Another organism rarely found outside of the catheterized urinary tract is Providencia stuartti. Other associated flora include Pseudomonas, ProteusMorganella and Acinetobacter species. Bacteriuria is polymicrobial in up to 95% of urine specimens. One-quarter of organisms in catheter urine are not present in urine simultaneously obtained by suprapubic bladder puncture, suggesting that some organisms only colonize the catheter.

Up to 50% of patients undergoing catheterization for more than 28 days’ experience recurrent encrustation and catheter blockage. Intermittent urinary retention can lead to vesicoureteral reflux and ascending complicated infection. Infecting organisms often include P. mirabilis on account of its properties as a potent producer of urease, which promotes the development of struvite stones by mechanisms which include hydrolysis of urea to ammonium. Bladder catheterization for more than 10 years as in patients with a spinal injury suggests that there is an increased risk of bladder cancer.

Alternative Methods of Urine Drainage

Prevention of catheter-associated infection may be best accomplished by finding alternatives to indwelling catheterization and perhaps treatment of bacteriuria.

- Intermittent catheterization

- Suprapubic catheterization

- Condom catheters

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Treatment (Table 1)

Treatment of asymptomatic bacteriuria

Asymptomatic bacteriuria should in general not be treated as it would only select complications of resistant organisms. Obviously there are occasional exceptions:

(a) treatment may be part of a plan to control nosocomial infection by a particularly virulent organism which is prevalent in a treatment unit

(b) patients who have a high risk of serious complications (granulocytopenia)

(c) patients undergoing urological surgery or implantation of prostheses

(d) patients with recurrent catheter obstruction and persistent infection with Proteus spp.

(e) patients infected with strains causing a high incidence of bacteremia, e.g. Serratia marcescens.

Usually, after catheter removal, the urinary tract will clear bacteria spontaneously. However, elderly females may need treatment, since bacteriuria in these patients may not resolve spontaneously.

Treatment of Symptomatic UTI

Parenteral antibiotics should be administered to catheterized patients who are febrile and ill, particularly if the blood culture is positive, though the results of culture may not become available in time to influence treatment decisions. Of course, other causes for pyrexia should be considered. Catheter removal should be considered as part of the treatment of symptomatic catheter-associated bacteriuria with the rationale that bacteria are sequestered within the biofilm coating the external and internal catheter surfaces.

After the initial administration of empirical treatment, the choice of antibiotic may need to be adjusted based on culture results of the urine and the catheter itself. Therefore before any antibacterial therapy is initiated, a urine sample for culture has to be taken. Long-term antibiotic treatment is not effective because the catheter acts as a foreign body. Urine cannot be permanently sterilized.

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Prevention of Cross-infection

Periurethral bacterial flora in the mucous sheath, surfaces of the catheter and drainage system, the reservoir of contaminated urine contained within it and the skin of the patient provide a source of infection to be readily transmitted on the hands of the medical and nursing staff. This may be reduced by treating the catheterized urinary tract as an open wound, and therefore using gloves after hand washing in antiseptic solutions.


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Table 1. Recommendations for Antimicrobial Therapy in Urology

Diagnosis  Most frequent pathogen/species Initial, empirical antimicrobial therapy Therapy duration
• E. coli
• Klebsiella
• Proteus
• Staphylococci
• Trimethoprim-sulphamethoxazole° 3 days
• Fluoroquinolone* (1-)3 days
• Fosfomycin trometamol 1 day
• Pivmecillinam (3-)7 days
• Nitrofurantoin (5-)7 days
• E. coli
• Proteus
• Klebsiella
• Other enterobacteria
• Staphylococci
• Fluoroquinolone*
• Cephalosporin (group 3a)
• Aminopenicillin/BLI
• Aminoglycoside

7-10 days
UTI with complicating factors
Nosocomial UTI
• E. coli
• Enterococci
• Pseudomonas
• Staphylococci
• Klebsiella
• Proteus
• Enterobacter
• Other enterobacteria
• Fluoroquinolone*
• Aminopenicillin/BLI
• Cephalosporin (group 2)
• Cephalosporin (group 3a)
• Aminoglycoside
In case of failure of initial therapy within 1-3 days or in clinically severe cases:
Anti-Pseudomonas active:
• Fluoroquinolone, if not used initially
• Acylaminopenicillin/BLI
• Cephalosporin (group 3b)
• Carbapenem
• ± Aminoglycoside

3-5 days after defeverescence or control/elimination of complicating factor
• (Candida) • Fluconazole
• Amphotericin B

• E. coli
• Other enterobacteria
• Pseudomonas
Alternative in acute bacterial prostatitis:
• Cephalosporin (group 3a/b)
2-4 weeks

4-6 weeks or longer

• Enterococci
• Staphylococci
• Chlamydia
• Ureaplasma
In case of Chlamydia or Ureaplasma:
• Doxycycline
• Macrolide
Urosepsis • E. coli
• Other enterobacteria
After urological interventions – multi-resistant pathogens:
• Pseudomonas
• Proteus
• Serratia
• Enterobacter
• Cephalosporin (group 3a/b)
• Fluoroquinolone*
• Anti-Pseudomonas active acylaminopenicillin/BLI
• Carbapenem
• Aminoglycoside
3-5 days after defeverescence or control/elimination of complicating factor
BLI = ß-lactamase inhibitor; UTI = urinary tract infection. *Fluoroquinolone with mainly renal excretion (see text). °Only in areas with resistance rate < 20% (for E. coli).

López-Medrano F, María Aguado J. Urinary Tract Infections in Transplant Recipients

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Muder RR, Brennen C, Rihs JC, Wagener MM, Obman A, Stout JE, Yu VL.  Isolation of Staphylococcus aureus from the Urinary Tract: Association of Isolation with Symptomatic Urinary Tract Infection and Subsequent Staphylococcal Bacteremia.  Clin Infect Dis 2006;42:46-50.



Clinical Manifestations





Urinary Tract Infections Catheter-Associated