Abstract:The objective of this study was to evaluate the incidence of infection and the risk factors associated to bacteraemia and mortality due to Methicillin-Resistant Staphylococcus Aureus (MRSA). This cohort study, conducted from August 2004 through November 2005, involved 60 consecutively identified patients with bloodstream MRSA infection. The control group included 240 non-infected patients, randomly selected and hospitalized on the day, or immediately after, results of blood culture of case patients were available. A case-control (1:4) study was conducted for evaluation of risk factors for bacteraemia and death. The incidence of infection was 1.99/1000 admissions. Mortality rates were 30% among patients and 5.38% among controls, with an attributed death rate of 24.6%. Multivariate analysis indicated the following risk factors for bacteraemia: severity predictors McCabe = 1, ASA>2 or APACHE II>10 (OR: 4.1; 95% CI: 1.8 -9.4) and use of central venous catheter (OR: 7.3; 95% CI: 2.4-22.2). University analysis showed as risk factors for mortality: age (OR: 1.08; 95% CI: 1.03-1.12), severity predictors McCabe = 1, ASA > 2 or APACHE II > 10 (OR: 9.13; 95% CI: 2.57-32.35), use of mechanical ventilation (OR: 10.32; 95% CI: 1.78-59.51) and use of corticoids (OR: 9.96; 95% CI: 2.69-36.78). Our results when investigating risk factors for bacteremia and mortality due to MRSA showed moderate influence of control group selection, in comparison to studies in which methicillinsensitive S. aureus infection is used as control.