Staphylococcus aureus bacteremia: clinical outcomes and predictors of 28-day mortality in a tertiary-care cohort

BACKGROUND: Staphylococcus aureus bacteremia (SAB) is associated with substantial short-term mortality, but the relative contributions of methicillin resistance, treatment adequacy, and host-related factors to outcome remain unclear. This study aimed to evaluate the clinical and microbiological characteristics of SAB, compare methicillin-resistant (MRSA) and methicillin-susceptible (MSSA) episodes, and identify independent predictors of 28-day mortality in a Turkish tertiary-care cohort. METHODS: This retrospective cohort study included adult patients hospitalized with monomicrobial S. aureus bacteremia at Eskisehir Osmangazi University Faculty of Medicine Hospital between January 2019 and May 2023. Demographic, clinical, microbiological, and treatment-related data were collected retrospectively. Factors associated with 28-day all-cause mortality were assessed using univariable and multivariable logistic regression analyses. RESULTS: A total of 372 patients were included, of whom 293 (78.8%) had MSSA bacteremia and 79 (21.2%) had MRSA bacteremia. The two groups were comparable with respect to age, comorbidity burden, illness severity, and source or presumed focus of infection. Appropriate empirical therapy was significantly more frequent in MSSA than in MRSA bacteremia (90.8% vs. 44.3%, p < 0.001), and time to appropriate therapy was shorter in the MSSA group (median 0 vs. 2 days, p < 0.001). Despite these differences, mortality did not differ significantly between MSSA and MRSA bacteremia at 7 days (14.3% vs. 15.2%, p = 0.848), cumulative 14 days (16.7% vs. 16.5%, p = 0.955), or 28 days (30.7% vs. 27.8%, p = 0.620). Overall, 28-day mortality was 30.1% (112/372). In multivariable analysis, older age (OR 1.03, 95% CI 1.01-1.05; p = 0.014), higher Pitt Bacteremia Score (OR 1.76, 95% CI 1.41-2.20; p < 0.001), and intensive care unit (ICU) admission (OR 2.87, 95% CI 1.62-5.09; p < 0.001) were independently associated with 28-day mortality. Methicillin resistance, appropriateness of empirical therapy, and time to appropriate treatment were not independently associated with mortality. CONCLUSIONS: In this cohort, short-term mortality in SAB was more strongly associated with host-related factors and acute illness severity than with methicillin resistance or treatment timing. Early risk stratification at the time of diagnosis may help guide the intensity of monitoring and management in patients with SAB.