Impact of methicillin-resistance on clinical outcomes in patients with Staphylococcus aureus bacteremia

OBJECTIVES: To estimate the impact of methicillin-resistance on in-hospital mortality, ICU admission, and length of stay among patients with Staphylococcus aureus bacteremia (SAB). METHODS: We conducted two retrospective cohort studies in Medellín, Colombia: an exploratory cohort from two referral hospitals (2007-2016) and a validation cohort from one hospital (2017-2023). Adults with S. aureus-positive blood cultures were included. Logistic regression models were used to evaluate associations between methicillin-resistance and in-hospital mortality or ICU admission. Competing risks regression was applied to assess length of stay. RESULTS: The exploratory cohort included 775 patients (MRSA: 23.6%) and the validation cohort 638 (MRSA: 32.9%). Methicillin-resistance was independently associated with increased ICU admission (exploratory aOR: 1.60; 95% CI: 1.07-2.40; validation aOR: 2.11; 95% CI: 1.25-3.60), but not with in-hospital mortality (exploratory aOR: 0.81; 95% CI: 0.52-1.26; validation aOR: 0.97; 95% CI: 0.60-1.56) or longer stay (exploratory aSHR: 0.93; 95% CI: 0.76-1.14; validation aSHR: 0.90; 95% CI: 0.74-1.10). Appropriate empiric therapy and timely culture-guided adjustments were protective. CONCLUSION: Across two independent cohorts, methicillin-resistance increased ICU admissions but not in-hospital mortality or length of stay. Tailored antimicrobial therapy and early interventions may improve outcomes in SAB.