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

Abstract

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 -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.