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 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.

FIGURE 1

Prevalence of multidrug-resistant (MDR), gram-negative bacteria among bloodstream isolates. Isolates were recovered from samples obtained within 48 hours after hospital admission from patients 65 years of age and older during an $8\frac{1}{2}\text{-year}$ study period. (P < .001)