Acquisition of multidrug-resistant Pseudomonas aeruginosa in patients in intensive care units: role of antibiotics with antipseudomonal activity.

A matched case-control study was performed to identify risk factors for acquiring multidrug-resistant Pseudomonas aeruginosa (MDRPA) in intensive care unit (ICU) patients during a 2-year period. MDRPA was defined as P. aeruginosa with combined decreased susceptibility to piperacillin, ceftazidime, imipenem, and ciprofloxacin. Thirty-seven patients who were colonized or infected with MDRPA were identified, 34 of whom were matched with 34 control patients who had cultures that showed no growth of P. aeruginosa. Matching criteria were severity of illness and length of ICU stay, with each control patient staying in the ICU for at least as long as the time period between the corresponding case patient's admission to the ICU and the acquisition of MDRPA. Baseline demographic and clinical characteristics and the use of invasive procedures were similar for case patients and control patients. Multivariate analysis identified duration of ciprofloxacin treatment as an independent risk factor for MDRPA acquisition, whereas the duration of treatment with imipenem was of borderline significance. These data support a major role for the use of antibiotics with high antipseudomonal activity, particularly ciprofloxacin, in the emergence of MDRPA.