Risk of mortality with a bloodstream infection is higher in the less severely ill at admission

Rationale: Health care-associated bloodstream infections are common in critically ill patients; however, investigators have had difficulty in quantifying the clinical impact of these infections given the high expected mortality among these patients. Objective: To estimate the impact of health care-associated bloodstream infections on in-hospital mortality after adjusting for severity of illness at critical care admission. Method: A cohort of medical and surgical intensive care unit patients. Measurements: Severity of illness at admission, bloodstream infection, and in-hospital mortality. Main Results: Among the 2,783 adult patients, 269 developed unit-associated bloodstream infections. After adjusting for severity of illness, patients with a lower initial severity of illness who developed an infection had a greater than twofold higher risk for in-hospital mortality (hazard ratio [HR] = 2.42, 95% confidence interval [CI] 1.70, 3.44) when compared with patients without infection and with a similar initial severity of illness. In contrast, patients with a higher initial severity of illness who subsequently developed an infection did not have an increased risk for in-hospital mortality (HR = 0.96, 95%CI 0.76, 1.23) when compared with patients without infection but with a similar initial severity of illness. Conclusions: These results suggest that these infections in less ill patients have a higher attributable impact on subsequent mortality than in more severely ill patients. Focusing interventions to prevent bloodstream infections in less severely ill patients would be expected to have a greater benefit in terms of mortality reduction.