Increased mortality associated with methicillin-resistant Staphylococcus aureus (MRSA) infection in the ICU: Results from the EPIC II study

Background: Controversy continues regarding whether the presence of methicillin resistance increases mortality risk in Staphylococcus aureus infections. We assessed the role of methicillin resistance on survival of patients with S. aureus infection in the EPIC II study cohort. Methods: The EPIC II point-prevalence study of infection in critically ill patients was performed on May 8, 2007. Demographic, physiological, bacteriological and therapeutic data were collected for 13,796 adult patients in 1,265 participating ICUs from 75 countries on the study day. ICU and hospital outcomes were recorded. We compared characteristics of patients with methicillin-sensitive (MSSA) and methicillin-resistant (MRSA) S. aureus infection. Comorbidities, age, SAPS II score and MRSA/MSSA were entered into a multivariable model and odds ratios (OR)[95% CI] for ICU and hospital mortality rates were calculated. Results: On the study day, 7,087 of the 13,796 patients (51%) were classified as infected. There were 494 patients with MRSA and 505 patients with MSSA infections. There were no significant differences between the two groups in use of mechanical ventilation or hemofiltration/hemodialysis. Cancer and chronic renal failure were more prevalent in MRSA than in MSSA patients. ICU mortality rates were 29.1% and 20.5%, respectively (p<0.01) and corresponding hospital mortality rates were 36.4% and 27.0% (P<0.01). Multivariable analyses of ICU and hospital mortality for MRSA infection showed an OR of 1.39[1.02-1.9], P=0.04 for ICU mortality and 1.37[1.03-1.83], P=0.03 for hospital mortality. Conclusion: In ICU patients, MRSA infection is associated with an almost 40% increase in adjusted ICU and hospital mortality risk compared to MSSA.