Epidemiology and risk factors for mortality among methicillin-resistant Staphylococcus aureus bacteremic patients in Southern Brazil

This study aimed to evaluate the epidemiology and 30-day mortality of adult patients with methicillin-resistant Staphylococcus aureus (MRSA) bacteremia. We retrospectively reviewed the demographic and clinical data of adult patients with S. aureus bloodstream infections (BSI), admitted to a tertiary public teaching medical center in Porto Alegre, Southern Brazil, from January 2014 to December 2019. A total of 928 patients with S. aureus BSI were identified in the study period (68.5 per 100,000 patient-years), and the proportion of MRSA isolates was 22% (19-27%). Thus, 199 patients were included in the analyses. The median age was 62 (IQR: 51-74) years, Charlson Comorbidity Index (CCI) median was 5 (IQR: 3-6), the Pitt bacteremia score (PBS) median was 1 (IQR: 1-4), and the most common site of infection was skin and soft tissue (26%). Most infections were hospital-acquired (54%), empirical anti-MRSA treatment was initiated in 34% of the cases, and in 44% vancomycin minimum inhibitory concentration was 1.5mg/L or above. Sixty-two (31.2%) patients died up to 30 days after the bacteremia episode. Patients with more comorbid conditions (higher CCI; aOR 1.222, p = 0.006) and a more severe presentation (higher PBS; aOR 1.726, p<0.001) were independently associated with mortality. Empiric antimicrobial therapy with an anti-MRSA regimen was associated with reduced mortality (aOR 0.319, p = 0.016). Our study identified significant risk factors for 30-day mortality in patients with MRSA BSI in a population with a high incidence of S. aureus bacteremia. Empiric treatment with an anti-MRSA drug was a protective factor. No significant variation in the incidence of S. aureus BSI was recorded throughout the period.