Risk Factors for Mortality in Staphylococcus aureus Bacteremia

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Abstract
To analyze risk factors for, and the role of methicillin resistance in, mortality in Staphylococcus aureus bacteremia. Nested case-control study. General teaching hospital with a high prevalence of methicillin-resistant Staphylococcus aureus (MRSA) strains, in São Paulo, Brazil. 136 patients over 14 years old with documented S aureus bacteremia. Those who died were compared with those who survived at least 14 days. Mortality within 14 days of bacteremia was 39% (53/136). Mean age was 47 years. Hospital-acquired bacteremia represented 86% (117/136) of episodes. In 26% (35/136), infection was related to an intravascular catheter and in 13% (17/136) to the respiratory tract. Septic shock occurred in 22% (30/136) of cases. MRSA was isolated in 66% (90/136). Multivariate analysis identified three variables that were significantly and independently associated with mortality: site of entry (lung, odds ratio [OR], 17.0; unknown, OR, 12.3; others, OR, 6.6); occurrence of shock (OR, 8.9), and resistance of S aureus to methicillin (OR, 4.2). Our study shows that S aureus bacteremia has a high mortality, especially when the lung is the source of infection and when shock develops; resistance to methicillin may be another risk factor for poor outcome.