A prospective study of pathogenesis of catheter-associated urinary tract infections.

OBJECTIVE To determine the pathogenesis of catheter-associated urinary tract infection (CAUTI) and the relative importance of each of the possible mechanisms of entry of infecting microorganisms to the catheterized urinary tract. MATERIAL AND METHODS We conducted a prospective study of 1,497 newly catheterized patients. Paired quantitative urine cultures were obtained daily, from the catheter specimen port and from the collection bag, using a technique that could detect 1 colony-forming unit/mL. We assumed that with extraluminal infections, caused by microorganisms ascending from the perineum in the mucous film contiguous to the external surface of the catheter, the organisms would be detected first in bladder urine or in far higher concentrations in urine from the specimen port than from the collection bag. With intraluminal CAUTIs, caused by microorganisms gaining access to the catheter lumen because of failure of closed drainage or contamination of collection bag urine, the organisms would be detected first or in far larger numbers in a collection bag specimen. RESULTS The probable mechanism of infection could be determined for 173 of 250 organisms (69.2 %) identified in 235 new-onset CAUTIs. Among these 173 cases, 115 (66%) were extraluminally acquired, and 58 (34%) were derived from intraluminal contaminants. For these determinable cases, CAUTIs caused by gram-positive cocci (enterococci and staphylococci) and yeasts were far more likely to be extraluminally acquired (extraluminal:intraluminal, 2.9) than were gram-negative bacilli, which caused CAUTIs by both routes equally (extraluminal: intraluminal, 1.2; P = 0.007). Surprisingly, no significant differences were noted in pathogenetic mechanisms between men and women. CONCLUSION We conclude that, in both men and women, CAUTIs occur by both extraluminal and intraluminal portals of entry but derive preponderantly from organisms that gain access extraluminally. Strategies for prevention of CAUTIs must focus on new technologies to prevent access of organisms by all possible routes.