AbstractObjective:To determine the relation between prior exposure to specific antimicrobials and acquisition of gram-negative bacilli resistant to multiple ß-lactam and aminoglycoside antibiotics among long-term-care patients.Design:Case-control study. Cases were patients from whom multiply resistantEnterobacteriaceaeorPseudomonas aeruginosawere isolated; controls were patients from whom nonresistant bacteria of the same species were isolated. Prospectively defined risk factors included underlying illness, activity level, presence of decu-bitus ulcers, presence of indwelling devices, and prior exposure to specific antimicrobial agents. Resistant and control isolates ofP aeruginosawere compared using pulsed-field gel electrophoresis (PFGE) of genomic DNA after digestion withXbaI.Setting:390-bed long-term Veterans' Affairs facility.Results:We identified 35 patients with multiply resistantEnterobacteriaceaeand 24 patients with multiply resistantP aeruginosa. Of the resistantEnterobacteriaceae, 87% of isolates were resistant to piperacillin, 55% to ceftazidime, and 90% to gentamicin. Acquisition of multiply resistantEnterobacteriaceaewas associated with presence of decubitus ulcers (odds ratio [OR], 12.2; 95% confidence interval [CI95], 3.3-44.2;P=.0002) and prior receipt of ampicillm (OR, 13.7; CI95, 2.2-84;P=.005). Of resistant isolates ofP aeruginosa, 88% were resistant to piperacillin, 25% to ceftazidime, 42% to imipenem, and 67% to ciprofloxacin. Isolation of a multiply resistantP aeruginosawas associated with total days of antimicrobial exposure (OR, 1.07; CI95, 1.01-1.12;P=.011) and not with prior receipt of any individual agent. Eleven multiply resistant isolates shared a common PFGE pattern.Conclusions:In our long-term-care facility, acquisition of multiply resistantEnterobacteriaceaewas associated with the presence of decubitus ulcers and prior exposure to ampicillin. Acquisition of resistantP aeruginosawas associated with total antibiotic exposure. Molecular typing ofP aeruginosaisolates implicated patient-to-patient transmission of a limited number of resistant strains.
Prevalence of multidrug-resistant organisms and risk factors for carriage in long-term care facilities: a nested case-control study
