Population-based assessment of intensive care unit-acquired bloodstream infections in adults: Incidence, risk factors, and associated mortality rate

Objective: Nosocomial bloodstream infections have been extensively investigated, but relatively few studies have specifically evaluated the epidemiology of intensive care unit-acquired bloodstream infections. The study objective was to define the incidence, risk factors, microbiology, and clinical outcomes of intensive care unit-acquired bloodstream infections. Design: Population-based prospective cohort. Setting: Multidisciplinary intensive care units. Patients: All Calgary Health Region (population 930,000) adult patients admitted to multidisciplinary intensive care units (≥48 hrs) from May 1, 1999, to April 30, 2000. Interventions: Blood sample analysis. Measurements and Results: There were 1,158 admission episodes in 1,017 patients; 37% involved females, and mean ± so age and Acute Physiology and Chronic Health Evaluation II scores were 59.6 ± 18.7 yrs and 23.4 ± 7.7, respectively. Fifty-one patients developed intensive care unit-acquired bloodstream infections (first positive blood culture ≥48 hrs after intensive care unit admission) for an incidence of 4.4% and an incidence density of 5.2 per 1000 intensive care unit days. Younger age (adjusted odds ratio, 0.98; 95% confidence interval, 0.95-1.00, p = .01), longer intensive care unit length of stay (adjusted odds ratio, 4.74; 95% Cl, 3.26-6.90, p < .001), and lower hematocrit (adjusted odds ratio, 0.95; 95% confidence interval, 0.90-1.00, p = .04) were significant independent predictors of intensive care unit-acquired bloodstream infections, and these infections were associated with an increased intensive care unit length of stay of 2.86 days (95% confidence interval, 2.29-3.57, p < .001). Staphylococcus aureus (27%), coagulase-negative staphylococci (14%), and Enterococcus faecium (12%) were most commonly isolated. Four (8%) bloodstream infections involved antibiotic-resistant organisms, and ten (20%) were polymicrobial. In multivariate analysis, intensive care unit-acquired bloodstream infection was associated with an increased intensive care unit mortality rate (adjusted odds ratio, 2.03; 95% confidence interval, 1.03-4.00, p = 0.04) but not overall hospital mortality rate. Conclusions: One patient in 20 admitted to Calgary Health Region intensive care units acquires bloodstream infection and suffers longer intensive care unit stay and increased mortality rates. In our region, multiple antibiotic-resistant organisms are uncommon causes of bloodstream infections, suggesting that it may be safe to use narrower spectrum empirical treatment regimens than current guidelines recommend.