MULTIPLY ANTIBIOTIC-RESISTANT GRAM-NEGATIVE BACILLI IN A LONG-TERM-CARE FACILITY - A CASE-CONTROL STUDY OF PATIENT RISK-FACTORS AND PRIOR ANTIBIOTIC USE

OBJECTIVE: To determine the relation between prior exposure to specifi c antimicrobials and acquisition of gram-negative bacilli resistant to multiple beta-lactam and aminoglycoside antibiotics among long-term-c are patients. DESIGN: Case-control study. Cases were patients from who m multiply resistant Enterobacteriaceae or Pseudomonas aeruginosa were isolated; controls were patients from whom nonresistant bacteria of t he same species were isolated. Prospectively defined risk factors incl uded underlying illness, activity level, presence of decubitus ulcers, presence of indwelling devices, and prior exposure to specific antimi crobial agents. Resistant and control isolates of P aeruginosa were co mpared using pulsed-field gel electrophoresis (PFGE) of genomic DNA af ter digestion with XbaI. SETTING: 390-bed long-term Veterans' Affairs facility. RESULTS: We identified 35 patients with multiply resistant E nterobacteriaceae and 24 patients with multiply resistant P aeruginosa . Of the resistant Enterobacteriaceae, 87% of isolates were resistant to piperacillin, 55% to ceftazidime, and 90% to gentamicin. Acquisitio n of multiply resistant Enterobacteriaceae was associated with presenc e of decubitus ulcers (odds ratio [OR], 12.2; 95% confidence interval [CI95], 3.3-44.2; P=.0002) and prior receipt of ampicillin (OR 13.7; C I95, 2.2-84; P=.005). Of resistant isolates of P aeruginosa, 88% were resistant to piperacillin, 25% to ceftazidime, 42% to imipenem, and 67 % to ciprofloxacin. Isolation of a multiply resistant P aeruginosa was 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. CONC LUSIONS: In our long-term-care facility, acquisition of multiply resis tant Enterobacteriaceae was associated with the presence of decubitus ulcers and prior exposure to ampicillin. Acquisition of resistant P ae ruginosa was associated with total antibiotic exposure. Molecular typi ng of P aeruginosa isolates implicated patient-to-patient transmission of a limited number of resistant strains (Infect Control Hosp Epidemi ol 1997;18:809-813).