Staphylococcus aureus bacteremia among elderly vs younger adult patients: comparison of clinical features and mortality.

BACKGROUND: Previous studies give conflicting results regarding the effect of age on outcomes in Staphylococcus aureus bacteremia (SAB). These studies have been limited by retrospective design or small sample size.
METHODS: We conducted a prospective cohort study of 385 patients with SAB aged 18 to 90 years. The setting was a large academic medical center. We observed patients from diagnosis of SAB to discharge or death. Discharged patients were contacted 12 weeks after their first positive culture findings. Data were collected on demographics, comorbid conditions, focus of infection, length of stay, and outcome. Primary outcomes were total mortality and death due to SAB.
RESULTS: Comparisons were made between 145 patients, aged 66 to 90 years, and 240 patients, aged 18 to 60 years. Forty-three (29.7%) of the elderly patients and 36 (15%) of the younger patients died. Death directly attributable to SAB occurred in 21 (14.5%) older and 15 (6.3%) younger patients. After adjusting for confounding variables, older patients continued to have higher total mortality (odds ratio, 2.21; 95% confidence interval, 1.32-3.70), and higher mortality from SAB (odds ratio, 2.30; 95% confidence interval, 1.13-4.69). Infection with methicillin-resistant S aureus was associated with higher total mortality in the elderly (odds ratio, 2.59; 95% confidence interval, 1.23-5.43).
CONCLUSIONS: Staphylococcus aureus bacteremia among the elderly is associated with high mortality. Both total mortality and mortality directly attributable to SAB are more than twice as likely in older patients. Infection with methicillin-resistant S aureus carries a worse prognosis than infection with methicillin-sensitive S aureus in the elderly.