• Early mortality in SAB is driven more by baseline clinical severity than by microbial phenotype. • ICU admission and an onset qSOFA ≥ 2 independently predict 30-day mortality. • MRSA phenotype was not independently associated with early mortality in adjusted models. • The prognostic contribution of SII appears limited in SAB/sepsis syndromes. • In this cohort, SII showed poor discrimination for early mortality and added little beyond severity markers (qSOFA/ICU requirement). To provide a practice-based interpretation of determinants of early mortality in Staphylococcus aureus bacteremia (SAB), with emphasis on host vulnerability and acute clinical severity relative to microbiological characteristics, inflammatory biomarkers, and early antimicrobial decision points. This single-center retrospective study included adult patients hospitalized with SAB between 2020 and 2025. Episodes with polymicrobial bacteremia were excluded. Clinical variables, including age, comorbidity burden (Charlson Comorbidity Index), qSOFA score, intensive care unit (ICU) admission, microbiological characteristics, antimicrobial therapy, and inflammatory markers—including the systemic immune–inflammation index (SII)—were collected. The primary outcome was 30-day mortality. Multivariable logistic regression analyses were performed to identify independent predictors of early mortality. Prespecified subgroup analyses evaluated the impact of empirical anti-MRSA therapy in non-complicated SAB and the prognostic performance of SII according to concurrent COVID-19 infection. A total of 407 patients with SAB were included (median age 67 years; 53.6% male). Thirty-day mortality was 36.1%. Older age, higher comorbidity burden, qSOFA score ≥ 2, ICU admission, and continuation of vancomycin therapy in MSSA bacteremia were independently associated with early mortality. In contrast, MRSA infection, persistent bacteremia, complicated SAB, and infective endocarditis were not associated with 30-day mortality. Although SII and procalcitonin levels were higher among non-survivors, SII demonstrated limited discriminatory performance (AUC 0.523) and was not independently predictive of early mortality. Empirical anti-MRSA therapy and treatment timing were not independently associated with early mortality after adjustment for baseline clinical severity. Early mortality in Staphylococcus aureus bacteremia appears to be determined primarily by host vulnerability and clinical severity at presentation rather than by pathogen-centered characteristics, treatment timing, or isolated inflammatory biomarkers. These findings suggest that early risk assessment in SAB should prioritise accurate characterisation of clinical severity to guide timely and proportionate management, rather than reliance on single microbiological or biomarker-based prognostic indicators.
Gürcüoğlu et al. (Wed,) studied this question.