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Describe catheter-associated urinary tract infection with its pathogenesis and prevention.

Microbiology · 2nd Professional — Para-Clinical

Pathogenesis

CAUTI is among the commonest healthcare-associated infections, and almost all hospital-acquired urinary infection is catheter-related
The risk is about 3 to 7% per day of catheterisation, and is essentially cumulative — so by 30 days nearly every catheterised patient is bacteriuric. duration is by far the dominant risk factor, which makes early removal the central preventive measure
Routes of entry — extraluminal (the commoner), with organisms from the perineum migrating up the outside of the catheter in the mucous sheath; and intraluminal, from contamination of the drainage system or reflux from the bag
Biofilm forms on the catheter within days — organisms embedded in a polysaccharide matrix on both surfaces, protected from antibiotics and from host defences. This is why bacteriuria cannot be eradicated while the catheter remains, and why treatment usually requires changing or removing it
Organisms — E. Coli, Klebsiella, Enterococcus, Pseudomonas, Candida, and proteus mirabilis, which is urease-producing: it splits urea, raises the urinary pH and precipitates struvite encrustation and blockage
Other risk factors — female sex, diabetes, older age, breaks in the closed system, and poor insertion technique

CLINICAL PEARL

Asymptomatic bacteriuria in a catheterised patient should not be treated, and usually should not even be tested for. Nearly every long-term catheterised patient is bacteriuric; treating it does not prevent symptomatic infection, does not clear the biofilm, and reliably selects resistant organisms. Sending a "routine" catheter urine in a patient with no symptoms generates a positive report that is very hard not to treat — so the discipline begins with not ordering the test. The exceptions are pregnancy and before urological surgery.

Diagnosis and Prevention

CAUTI requires symptoms plus bacteriuria. In a catheterised patient the usual symptoms of dysuria and frequency are absent, so the features are fever with no other source, suprapubic or flank tenderness, rigors, new confusion in the elderly, or haematuria. Cloudy or offensive urine alone is not an indication to treat
Specimen — taken aseptically from the sampling port after disinfection, never from the drainage bag (which reflects bag flora) and never by disconnecting the system. Ideally the catheter is replaced first and the sample taken from the new one, since the old catheter's biofilm contaminates the specimen
Significant count — conventionally 105 colony-forming units per mL, but 103 is significant in a symptomatic catheterised patient; pyuria is present in nearly all catheterised patients and does not distinguish infection from colonisation

Bundle element	Detail
Avoid the catheter	Insert only for a defined indication — acute retention or obstruction, accurate output measurement in critical illness, selected surgery, sacral wound care in incontinence, and comfort in terminal care. Incontinence alone and staff or ward convenience are not indications
Consider alternatives	Intermittent catheterisation, condom drainage in men, bedside commode, timed voiding and absorbent pads
Aseptic insertion	Trained staff, hand hygiene, sterile gloves and equipment, antiseptic periurethral cleaning, single-use lubricant, and the smallest catheter that will drain
Maintain a closed system	Never disconnect the catheter from the drainage tube; sample only from the port; secure the catheter to prevent traction and urethral trauma
Keep the bag below the bladder	And off the floor, with the tubing free of kinks — to prevent reflux, which is a direct route for organisms into the bladder
Review daily and remove	The single most effective measure. Automatic stop orders, nurse-initiated removal protocols and daily reminders all reduce catheter-days and hence infection
What does not help	Routine catheter changes at fixed intervals; bladder irrigation with antiseptics or antibiotics; instilling antiseptic into the drainage bag; systemic antibiotic prophylaxis; and routine meatal antiseptic application — all of which are still widely practised and none of which is beneficial

Treatment and Applied Aspects

Remove the catheter if possible, or replace it if it must stay and has been in place for more than a week; this removes the biofilm and measurably improves the response to treatment
Treat symptomatic infection with a 7-day course guided by culture and local resistance patterns, and de-escalate when sensitivities are available; longer courses are needed for delayed response or bacteraemia
Do not treat asymptomatic bacteriuria or candiduria; for candiduria in a catheterised patient, removing or changing the catheter clears most cases without any antifungal
Ask daily whether the catheter is still needed, and record the indication; in practice a large proportion of catheters in Indian wards have no current indication and are simply never removed
Educate about bag position; a drainage bag placed on the bed or lifted above the bladder during transfer allows reflux, and this is among the commonest observed lapses
Consider Proteus when a catheter blocks repeatedly or the urine is alkaline and encrusted; a urease-producing organism will continue to block catheters until it is addressed

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