The Rising Influx of Multidrug-Resistant Gram-Negative Bacilli into a Tertiary Care Hospital

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Abstract
Background. The prevalence of multidrug resistance (MDR) among gram-negative bacilli is rapidly increasing. Quantification of the prevalence and the common antimicrobial coresistance patterns of MDR gram-negative bacilli (MDR-GNB) isolates recovered from patients at hospital admission, as well as identification of patients with a high risk of harboring MDR-GNB, would have important implications for patient care. Methods. Over a 6-year period, patients who harbored MDR-GNB (i.e., patients who had MDR-GNB isolates recovered from clinical cultures within the first 48 h after hospital admission) were identified. “MDR-GNB isolates” were defined asPseudomonas aeruginosa, Escherichia coli, Enterobacter cloacae, andKlebsiella species isolates with resistance to at least 3 antimicrobial groups. A case-control study was performed to determine the independent risk factors for harboring MDR-GNB at hospital admission. Results. Between 1998 and 2003, the prevalence of MDR-GNB isolates recovered from patients at hospital admission increased significantly for all isolate species (P < .001), with the exception ofP. aeruginosa (P = .09). Of 464 MDR-GNB isolates, 12%, 35%, and 53% of isolates were coresistant to 5, 4, and 3 antimicrobial groups, respectively. Multivariable analysis identified age ⩾65 years (odds ratio [OR], 2.8; 95% confidence interval [CI], 1.1–7.4;P < .04), prior exposure to antibiotics for ⩾14 days (OR, 8.7; 95% CI, 2.5 –30;P < .001), and prior residence in a long-term care facility (OR, 3.5; 95% CI, 1.3–9.4;P < .01) as independent risk factors for harboring MDR-GNB at hospital admission. Conclusion. A substantial number of patients harbor MDR-GNB at hospital admission. Identification of common coresistance patterns among MDR-GNB isolates may assist in the selection of empirical antimicrobial therapy for patients with a high risk of harboring MDR-GNB.

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