Epidemiology and clinical characteristics of Staphylococcus aureus bloodstream infections in a tertiary-care center in Mexico City: 2003-2007.

OBJECTIVE: To compare the epidemiology, clinical variables, outcome and molecular characteristics between methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) bloodstream infections (BSI) of patients from a tertiary-care center.

METHODS: We conducted a five-year retrospective cohort analysis of all patients with at least one peripherally-drawn blood culture positive for S. aureus. Patient characteristics, clinical data and outcome were analyzed, as well as microbiologic data.

RESULTS: We included 444 isolates derived from 172 patients. The highest rate of MRSA BSI was observed in 2005 (4.9 cases per 1,000 patients). MRSA BSIs were more likely to be originated from a skin and soft tissue infection (OR 2.44, CI 95% 1.05-5.67, p = 0.03). The only significant risk factor for MRSA BSI was the mean length of hospital stay (OR 1.01; CI 95% 1.00-1.02, p = 0.002). A difference in inadequate initial treatment was noticed in MRSA BSI (OR 8.35 CI 95% 1.55-8.39, p = 0.002); but it had no impact on mortality. All MRSA isolates were SCCmec type II, and we did not find any resistance to vancomycin or linezolid.

CONCLUSION: MRSA BSIs were associated with a prolonged hospital stay. We did not observe any difference in mortality between MRSA and MSSA BSIs. During the study period, we only identified SCCmec type II in MRSA isolates, which suggests that this infection was hospital- acquired.