Hospital-Level Rates of Fluoroquinolone Use and the Risk of Hospital-Acquired Infection with Ciprofloxacin-Nonsusceptible Pseudomonas aeruginosa

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In recent years, Pseudomonas aeruginosa has become increasingly resistant to fluoroquinolones, and fluoroquinolone use in the United States has also increased. Our objective was to determine whether higher hospital-level rates of use of ciprofloxacin, levofloxacin, and moxifloxacin antimicrobials were predictors that a higher proportion of P. aeruginosa isolates from hospital-acquired infections (hereafter, "hospital-acquired isolates") would be nonsusceptible to ciprofloxacin. We identified all hospital-acquired isolates from 14 hospitals in the Northern California Kaiser Permanente health care delivery system between 1998 and 2003 and determined their susceptibility to ciprofloxacin. For each facility, we determined the number of days of fluoroquinolone use per 1000 patient-days, by calendar quarter. We used a logistic regression model to analyze the data, with susceptibility status as the outcome variable. Hospital-level rates of use of the 3 fluoroquinolones were the predictors of interest; we adjusted for year, for use of nonquinolone antimicrobials, and for patient variables, including the number of days spent in the hospital in the prior year and fluoroquinolone use in the prior year. The model tested whether isolates from those facilities with higher rates of use of antimicrobials were more likely to be nonsusceptible to ciprofloxacin. Of 6099 isolates tested, 15% were not susceptible to ciprofloxacin. The nonsusceptibility rate increased from 9% to 20% between 1998 and 2003. Both the overall rate of use at the hospital and prior patient-specific use of ciprofloxacin, levofloxacin, and moxifloxacin were found to be independent predictors that a subsequent P. aeruginosa isolate would be nonsusceptible to ciprofloxacin. Higher hospital-level rates of use of ciprofloxacin, levofloxacin, and moxifloxacin are each associated with an increased proportion of hospital-acquired P. aeruginosa isolates being nonsusceptible to ciprofloxacin.