Influx of Multidrug-Resistant, Gram-Negative Bacteria in the Hospital Setting and the Role of Elderly Patients With Bacterial Bloodstream Infection

BACKGROUND. Multidrug-resistant (MDR) gram-negative bacteria are reported increasingly frequently among isolates recovered from elderly patients. The clinical epidemiology of bloodstream infection (BSI) due to MDR gram-negative bacteria among elderly patients is unknown. OBJECTIVE. To characterize the clinical epidemiology of BSI due to MDR gram-negative bacteria among elderly patients at hospital admission in an effort to provide a greater understanding of these serious infections and ultimately to improve patient outcomes. DESIGN. Case-control study. SETTING. Tertiary care hospital in Boston, Massachusetts. PATIENTS. Patients 65 years of age and older. METHODS. From 1999 to 2007, computerized medical records were reviewed for BSI due to MDR gram-negative bacteria within 48 hours of hospital admission. Risk factors for BSI due to these bacteria were identified. RESULTS. MDR gram-negative bacteria were recovered from 61 (8%) of 724 elderly patients with BSI caused by gram-negative bacteria. Over the 8 1/2-year study period, the percentage of MDR gram-negative bacteria among bloodstream isolates increased from 2 (1%) of 199 to 34 (16%) of 216. Empiric therapy was ineffective for 38 (63%) of 60 patients with BSI caused by MDR gram-negative bacteria. The variables independently associated with BSI due to these bacteria were as follows: residency in a long-term care facility (odds ratio [OR], 4.9 [95% confidence interval {CI} 1.6-14.9]; P = .006), presence of an invasive device (OR, 6.0 [95% CI, 1.5-23.5]; P = .01), severe sepsis (OR, 7.9 [95% CI, 1.7-37.1]; P = .009), and delayed initiation of effective therapy (OR, 12.8 [95% CI, 3.9-41.1]; P < .001). CONCLUSION. The 16-fold increase in BSI due to MDR gram-negative bacteria at hospital admission among elderly patients, especially among those who resided in long-term care facilities prior to admission, contributes further to the expanding body of evidence that these patients are the main reservoirs of MDR gram-negative bacteria. Given their contribution to the influx of antimicrobial-resistant bacteria in the hospital setting, infection control interventions that target this high-risk group need to be considered.