Objectives.To determine the predictors of 7‐day mortality in older adult patients with Staphylococcus aureus bacteremia after controlling for comorbidity using the Charlson weighted index of comorbidity (WIC) and to identify the risk factors associated with bacteremia due to methicillin‐resistant S. aureus (MRSA).

Design.Retrospective cohort study from January 2003 until December 2004.

Setting.Two tertiary care, university‐affiliated hospitals.

Methods.One hundred thirty‐five hospitalized patients with S. aureus bacteremia were included in the study. All patients who were 60 years or older and had 1 or more blood cultures positive for S. aureus were included in the study. The primary outcome was death 7 days after the onset of S. aureus bacteremia.

Results.Twenty‐one patients (15.6%) died within 7 days after the onset of S. aureus bacteremia. Seventy‐four patients (56.1%) had MRSA bacteremia. Multivariate analysis identified 3 independent determinants of 7‐day mortality: Charlson WIC score greater than 5 (odds ratio [OR], 3.6 [95% confidence interval {CI}, 1.1‐11.2]; ), previous hospitalization in the past 3 months (OR, 5.0 [95% CI, 1.1‐25.1]; ), and altered mental status at the onset of S. aureus bacteremia (OR, 13.6 [95% CI, 2.9‐64.6]; ). Multivariate analysis identified previous hospitalization in the past 3 months (OR, 2.6 [95% CI, 1.1‐5.9]; ), residence in a long‐term care facility (OR, 4.5 [95% CI, 1.7‐12.3]; ), and altered mental status at the onset of S. aureus bacteremia (OR, 2.5 [95% CI, 1.5‐5.6]; ) to be independently associated with the presence of MRSA.

Conclusions.The Charlson WIC is significantly associated with increased mortality of S. aureus bacteremia in older adults. Previous hospitalization in the past 3 months, residence in a long‐term care facility, and altered mental status should be used as a guidance for empirical vancomycin therapy and application of infection control measures in older adults with suspected S. aureus bacteremia.