The presence of a urethral catheter is associated with a 3–8% incidence of significant bacteriuria (≥10⁵ colony forming units/mL) per day (1). This is assumed to be the result of bacterial migration along the outer surface of the catheter and into the bladder.

Bacteria also form biofilms on the inner and outer surface of urethral catheters (2), and these biofilms can serve as a source of continued microbial colonization in the bladder.

Bacterial migration and biofilm formation are not the whole story, because direct injection of pathogens into the bladder of healthy subjects does not result in a UTI (3). Epithelial cells of the bladder are coated with non-pathogenic organisms (4), which prevent the attachment of
pathogens (5), and it is possible that a change in bacterial adherence serves as a prelude to UTI.

The pathogens isolated in catheter-associated bacteriuria are shown in Table 33.1 (6).

The predominant organisms are gram-negative aerobic bacilli (especially Escherichia coli), enterococci, and Candida species, while staphylococci are infrequent isolates.

A single organism predominates in bacteriuria associated with short-term catheterization (<30 days), whereas bacteriuria is often polymicrobial in long-term catheterization (≥30 days).

The risk of catheter-associated infection is determined primarily by the duration of catheterization (1), so removing catheters when they are no longer necessary is the single most effective prophylactic measure for catheter-associated infections.

Urinary catheters impregnated with antimicrobial agents (silver alloy or nitrofurazone) can reduce the incidence of asymptomatic bacteriuria in short-term catheterization (<1 week) (7), but the benefit in preventing symptomatic urinary tract infections is not clear (1).

The following practices are NOT recommended (1):