To determine risk factors and outcomes associated with ciprofloxacin resistance in clinical bacterial isolates from intensive care unit (ICU) patients.

Prospective cohort study.

Twenty-bed medical-surgical ICU in a Canadian tertiary care teaching hospital.

All patients admitted to the ICU with a stay of at least 72 hours between January 1 and December 31, 2003.

Prospective surveillance to determine patient comorbidities, use of medical devices, nosocomial infections, use of antimicrobials, and outcomes. Characteristics of patients with a ciprofloxacin-resistant gram-negative bacterial organism were compared with characteristics of patients without these pathogens.

Ciprofloxacin-resistant organisms were recovered from 20 (6%) of 338 ICU patients, representing 38 (21%) of 178 nonduplicate isolates of gram-negative bacilli. Forty-nine percent of Pseudomonas aeruginosa isolates and 29% of Escherichia coli isolates were resistant to ciprofloxacin. In a multivariate analysis, independent risk factors associated with the recovery of a ciprofloxacin-resistant organism included duration of prior treatment with ciprofloxacin (relative risk [RR], 1.15 per day [95% confidence interval {CI}, 1.08-1.23]; P < .001), duration of prior treatment with levofloxacin (RR, 1.39 per day [95% CI, 1.01-1.91]; P = .04), and length of hospital stay prior to ICU admission (RR, 1.02 per day [95% CI, 1.01-1.03]; P = .005). Neither ICU mortality (15% of patients with a ciprofloxacin-resistant isolate vs 23% of patients with a ciprofloxacin-susceptible isolate; P = .58 ) nor in-hospital mortality (30% vs 34%; P = .81 ) were statistically significantly associated with ciprofloxacin resistance.

ICU patients are at risk of developing infections due to ciprofloxacin-resistant organisms. Variables associated with ciprofloxacin resistance include prior use of fluoroquinolones and duration of hospitalization prior to ICU admission. Recognition of these risk factors may influence antibiotic treatment decisions.