Abstract
BackgroundAppropriate empiric therapy, antibiotic therapy with in vitro activity to the infecting organism given prior to confirmed culture results, may improve Staphylococcus aureus outcomes. We aimed to measure the clinical impact of appropriate empiric antibiotic therapy on mortality, while statistically adjusting for comorbidities, severity of illness and presence of virulence factors in the infecting strain.MethodologyWe conducted a retrospective cohort study of adult patients admitted to a tertiary-care facility from January 1, 2003 to June 30, 2007, who had S. aureus bacteremia. Time to appropriate therapy was measured from blood culture collection to the receipt of antibiotics with in vitro activity to the infecting organism. Cox proportional hazard models were used to measure the association between receipt of appropriate empiric therapy and in-hospital mortality, statistically adjusting for patient and pathogen characteristics.Principal FindingsAmong 814 admissions, 537 (66%) received appropriate empiric therapy. Those who received appropriate empiric therapy had a higher hazard of 30-day in-hospital mortality (Hazard Ratio (HR): 1.52; 95% confidence interval (CI): 0.99, 2.34). A longer time to appropriate therapy was protective against mortality (HR: 0.79; 95% CI: 0.60, 1.03) except among the healthiest quartile of patients (HR: 1.44; 95% CI: 0.66, 3.15).Conclusions/SignificanceAppropriate empiric therapy was not associated with decreased mortality in patients with S. aureus bacteremia except in the least ill patients. Initial broad antibiotic selection may not be widely beneficial.
Highlights
Staphylococcus aureus bacteremia is associated with considerable excess morbidity, mortality, and healthcare costs [1,2]
Among the 814 patients included in the study, 537 (66%) received appropriate empiric therapy and 109 (13%) patients died within 30 days of culture collection
Patients who received appropriate empiric therapy were more likely to be infected with methicillin-susceptible S. aureus (MSSA), to have a polymicrobial infection, to have a higher severity of illness score, to be an injection drug user, to be previously hospitalized in the past year and to have renal disease (p,0.05)
Summary
Staphylococcus aureus bacteremia is associated with considerable excess morbidity, mortality, and healthcare costs [1,2]. Antibiotic therapy with in vitro activity to the infecting organism given prior to known culture results, known as appropriate empiric antibiotic therapy, may improve patient outcomes [4,5,6,7,8,9,10]. Previous studies of the association between appropriate antibiotic therapy for S. aureus infections and mortality, have demonstrated conflicting results [4,5,6,7,8,9,10,11,12,13,14,15,16] The differences in these results may be due to different methods of measuring exposures and outcomes, failure to control for necessary confounders such as severity of illness, or incorrectly statistically adjusting for variables which are part of the causal pathway between infection and mortality [17,18]. Appropriate empiric therapy, antibiotic therapy with in vitro activity to the infecting organism given prior to confirmed culture results, may improve Staphylococcus aureus outcomes. We aimed to measure the clinical impact of appropriate empiric antibiotic therapy on mortality, while statistically adjusting for comorbidities, severity of illness and presence of virulence factors in the infecting strain
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