[Bacteremia by Staphylococcus aureus: analysis of 311 episodes].

Background: The aim of this study was to set up the differences between nosocomial and community acquired S. aureus bacteremia, to identify the features of the patients at high risk of endocarditis and to define the characteristics of the patients with methicillin resistant S. aureus (MRSA).
Methods: We prospectively studied 311 cases of S. aureus bacteremia detected at our hospital during a four-year period.
Results: Nosocomial acquisition of bacteremia was found in 63% of the cases, 45% of which were caused by MRSA. Nosocomial bacteria generally presented in older patients with more severe underlying conditions and a higher prevalence of invasive procedures than patients with the community-acquired disease. Likewise, the primary focus of infection was identifiable in most of the nosocomial episodes and mortality was also higher. Endocarditis presented in 19% of the bacteremia episodes and almost 90% of patients with endocarditis were intravenous drug users (IDU). The risk of endocarditis in this group was 64% whereas it was only 3% in non-IDU patients. Overall mortality was 33% and mortality directly due to the bacteremia was 22%.
Conclusions: IDU patients were at high risk of endocarditis but most had a favourable outcome. Bacteremia was community-acquired in these patients and they rarely presented MRSA bacteremia. Patients with previous valvular diseases were at high risk of endocarditis and had a high mortality. Non-IDU patients with community-acquired bacteremia were at a low risk of endocarditis, regardless of whether a primary focus of infection had been identified or not. Mortality was lower in this group than in patients with nosocomial bacteremia and there were no cases of MRSA bacteremia. Mortality was higher in patients treated with vancomycin than in patients treated with other antibiotics active against S. aureus.