Introduction

Urinary tract infections (UTIs) are the most common hospital-acquired infection.

Nosocomial UTIs delay recovery and can lead to complications including:

• Pyelonephritis
• Bacteraemia. 

Nosocomial UTI may lead to bacteraemia with a subsequent mortality of up to 30%.

The single greatest risk factor for nosocomial UTI is urinary catheterisation.

Approximately 10% of all patients will be catheterised during their hospital stay, for a mean of four days.  The risk of developing bacteriuria is about 5% for each day a patient is catheterised. Up to 20% of catheterised patients will develop bacteriuria and up to 6% develop symptoms of UTI.

Because catheters readily become colonised, it is important to distinguish urinary tract infection from asymptomatic bacteriuria in catheterised patients. Treating asymptomatic bacteriuria in catheterised patients with antibiotics is not associated with a reduction in the incidence of UTI but is associated with an increase in resistant uropathogens, including Candida spp.

Asymptomatic catheter-associated bacteriuria should not be treated.

Asymptomatic bacteriuria in catheterised patients is not usually clinically significant and often resolves spontaneously when the catheter is removed.  However, patients remain at increased risk of developing a UTI for up to 30 days after catheter removal.

Pathogenesis of catheter-associated bacteriuria

Aetiology of nosocomial UTI

The same organisms are responsible for asymptomatic bacteriuria and symptomatic UTI so it is impossible to differentiate between infection and colonisation by the organism involved. Causative organisms are primarily faecal or from the skin flora. Catheter urines frequently yield mixed cultures. Common pathogens include:

• Enterobacteriaceae
  • Escherichia coli (50% of infections)
• Staphylococcus spp.
  • Staphylococcus aureus (including MRSA)
• Staphylococcus epidermidis
• Enterococcus spp.
  • Enterococcus faecalis
• Oxidase-positive Gram-negative organisms
• Pseudomonas aeruginosa
• Fungi
  • Candida spp.

Diagnosis of nosocomial UTI

1.      Non-catheterised patients

In non-catheterised patients, the clinical and microbiological diagnosis of a nosocomial UTI is essentially the same as the diagnosis of community-acquired UTI, eg. significant bacteriuria associated with signs and symptoms of infection.

2.      Catheterised patients

Diagnosis of UTI in catheterised patients is problematic in that many of the usual laboratory and microbiological parameters are unreliable indicators of infection in the presence of a catheter. The presence of the catheter can mask or mimic the classical signs and symptoms of UTI, in particular, significant bacteriuria, pyuria and suprapubic pain.

• Significant bacteriuria: catheters readily become colonised so catheter urines will frequently yield cultures (often mixed cultures).
• Pyuria: the irritation from the catheter can result in pyuria despite the absence of infection. Conversely, even if infection is present causing pyuria, the altered pH in catheter urine and in urine following infection with certain organisms such as Proteus spp. can lyse white blood cells so they may not be detectable.
• Suprapubic pain: the presence of the catheter can cause suprapubic pain in some individuals.

Clinical symptoms are the key to diagnosis of infection in catheterised patients.

Symptoms indicative of infection in immunocompetent patients include:

• Fever
• Haematuria.

Laboratory diagnosis

Because colonisation of catheters is common, specimens should only be taken from catheterised patients when the patient is febrile.

Specimens should be taken from the catheter, not from the bag, which readily becomes colonised. Catheter urines frequently yield mixed cultures; while this does not necessarily mean that the infection is polymicrobial, it gives an indication of the types of pathogen that need to be covered by antibiotic therapy.

Management of bacterial nosocomial UTI

1.      Non-catheterised patients

• Nosocomial infections in non-catheterised patients are usually monomicrobial but are more likely than community-acquired infections to involve resistant organisms, and therefore empirical antibiotic choice should include consideration of previous antibiotic therapy and local resistance patterns. Consult your microbiologist.

Refer to local treatment recommendations for nosocomial UTI.

• Once culture results and sensitivities are known, antibiotic therapy can be amended if necessary.
• In non-complicated infection, treatment durations are the same as those for community-acquired disease
• If complicated infection is suspected, discuss treatment with the local microbiologist.

2.      Catheterised patients

Colonisation of catheters is common.
Asymptomatic catheter-associated bacteriuria should not be treated.

Infections in patients with neuropathic bladders require special management and should be treated in consultation with the local team.

The management of patients with short-term acute catheters and long-term indwelling catheters follow the same general approach but the goals are different. In patients with short-term acute catheters, the goal is to keep the patient well until they no longer need the catheter. In patients with long-term indwelling catheters, the goal is to resolve febrile episodes. It is not possible to render the urinary tract permanently sterile in long-term catheterised patients.

General management steps are:

• Remove the catheter, if possible.  If not, then:
  • Change the catheter (to remove the bacterial biofilm leading to the bladder). Changing the catheter before starting antibiotic treatment is associated with shorter febrile periods and reduced rate of symptomatic relapse.
  • Insert the new catheter under prudent antibiotic cover.

Antibiotic rationale

• Cultures from catheterised patients are often polymicrobial but it is not possible to identify which organisms are responsible for the symptoms, and therefore empirical antibiotics must be directed against the organisms isolated.
• Since hospital infections are more likely than community-acquired infections to involve resistant organisms, the antibiotics chosen must be active against the local flora. Consult your microbiologist.

Refer to local treatment recommendations for management of catheter-associated UTI.

• Once culture results and sensitivities are known, antibiotic therapy can be amended if necessary.

Duration of treatment

• The optimal duration of therapy is not defined, and hence should be guided by clinical response on an individual patient basis.  Pyelonephritis should always be excluded and if present, therapy may be prolonged to 14–21 days.

Do not perform repeat urine cultures to monitor treatment in catheterised patients.

The high colonisation rate means that no useful information is obtained from this test. The success of treatment in catheterised patients is measured by the resolution of symptoms. Treatment failure is the return of fever, not the return of bacteriuria.

Prevention of catheter-associated UTI

Management of fungal nosocomial UTI

Flow chart for empirical management of nosocomial UTIs.  Treatment suggestions are general empirical choices and may not be suitable for all centres. Refer to local guidelines.