Epidemiology and outcome of nosocomial bloodstream infection in elderly critically ill patients: a comparison between middle-aged, old, and very old patients.

Background: We investigated the epidemiology of nosocomial bloodstream infection in elderly intensive care unit (ICU) patients.

Methods: In a single-center, historical cohort study (1992-2006), we compared middle-aged (45-64 years; n = 524), old(65-74 years; n = 326), and very old ICU patients (> 75 years; n = 134) who developed a nosocomial bloodstream infection during their ICU stay.

Results: Although the total number of ICU admissions (patients aged > or = 45 years) decreased by approximately 10%, the number of very old patients increased by 33% between the periods 1992-1996 and 2002-2006. The prevalence of bloodstream infection (per 1,000 ICU admissions) increased significantly over time among old (p = 0.001) and very old patients (p = 0.002), but not among middle-aged patients (p = 0.232). Yet, this trend could not be confirmed with the incidence data expressed per 1,000 patient days (p > 0.05). Among patients with bloodstream infection, the proportion of very old patients increased significantly with time from 7.2% (1992-1996) to 13.5% (1997-2001) and 17.4% (2002-2006) (p <0.001). The incidence of bloodstream infection (per 1000 patient days) decreased with age: 8.4 per thousand in middle-aged, 5.5 per thousand in old, and 4.6 per thousand in very old patients (p < 0.001). Mortality rates increased with age: 42.9%, 49.1%, and 56.0% for middle-aged, old, and very old patients, respectively (p = 0.015). Regression analysis revealed that the adjusted relationship with mortality was borderline significant for old age (hazard ratio, 1.2; 95% confidence interval, 1.0 -1.5) and significant for very old age (hazard ratio,1.8; 95% confidence interval, 1.4 -2.4).

Conclusion: Over the past 15 years, an increasing number of elderly patients were admitted to our ICU. The incidence of nosocomial bloodstream infection is lower among very old ICU patients when compared to middle-aged and old patients. Yet, the adverse impact of this infection is higher in very old patients.