383. Characterization of Methicillin-Resistant Staphylococcus aureus (MRSA) in Patients with Bloodstream Infection (BSI) Identified by the Canadian Nosocomial Infection Surveillance Program (CNISP), 2008-2010
Session: Poster Abstract Session: MRSA, MSSA, Enterococci
Thursday, October 3, 2013
Room: The Moscone Center: Poster Hall C
Background: MRSA BSI is associated with significant mortality and morbidity.  In this study we characterized MRSA BSI isolates and investigated associations with outcome. 

Methods: Prospective surveillance for MRSA BSI was done in 54 Canadian hospitals from 2008-2010.  Clinical and epidemiologic data were collected by experienced infection control professionals.  30-day all-cause mortality was determined.   A blood culture isolate from each of 791 patients was characterized by spa and SCCmec typing.  Panton Valentine leukocidin (PVL) gene was detected by PCR.  Antimicrobial susceptibility testing was done by broth microdilution. 

Results: 1,053 patients with MRSA BSI were identified (0.48/1,000 admissions).  24% had primary bacteremia, and other major sources of infection were skin/soft tissue (30%), and pneumonia (14%); 3% had endocarditis.  The most common strains resembled USA100/800, Ridom spa type t002 (57% of isolates), and USA300, t008 (27%).  PVL was detected in 223 (28%) isolates.  USA300 was more commonly identified in western provinces, whereas USA100/800 was predominant in the rest of the country.  USA300 BSI isolates were more likely to be community-associated (50% vs 7%; p<0.001), to be recovered from younger patients (mean age 51 yrs vs 67 yrs; p<0.001), and to be associated with skin/soft tissue infection (33% vs 19%; p<0.001) or pneumonia (23% vs 15%; p=0.03).  BSI caused by USA100/800 was associated with primary bacteremia (30% vs 18%; p=0.004) and surgical site infection (13% vs 6%; p=0.02).  Resistance to vancomycin, linezolid, or daptomycin was not identified; only 0.8% isolates had vancomycin MIC=2.0 µg/ml.  The 30-day crude mortality was 23.4%.  Mortality was associated with older age (> 65 yrs) (p<0.001), healthcare-associated BSI (OR 1.35, 95% CI 1.04-1.6; p=0.04), pneumonia (OR 3.54, 95% CI 2.5-5.1; p<0.001), and with isolates harboring SCCmec type II (OR 1.4, 95% CI 1.1-1.6; p=0.004).  Mortality was not associated with strain type, presence of PVL, or vancomcyin MIC ≥ 1.5 µg/ml. 

Conclusion: USA300 accounted for 27% of MRSA BSIs from 2008-2010, of which 50% were acquired in a healthcare facility.  Host factors (age, infection site) were associated with increased mortality; strain type, PVL, and reduced susceptibility to vancomycin were not associated with outcome.

George Golding, PhD, National Microbiology Laboratory, Public Health Agency of Canada, Winnipeg, MB, Canada, Andrew E. Simor, MD, FRCPC, FACP, Department of Microbiology, Sunnybrook Health Sciences Centre, Toronto, ON, Canada, Linda Pelude, MSc, Public Health Agency of Canada, Ottawa, ON, Canada, Elizabeth Bryce, MD FRCPC, Pathology and Laboratory Medicine, Vancouver Coastal Health, Vancouver, BC, Canada, Charles Frenette, MD, Infectious Diseases and Medical Microbiology, McGill University Health Centre, Montreal, QC, Canada, Kevin Katz, MD CM, MSc, Infection Prevention & Control, North York General Hospital, Toronto, ON, Canada, Mark Loeb, MD, MSc, McMaster University, Hamilton, ON, Canada, Allison McGeer, MD, FRCPC, Public Health Sciences & Pathobiology, University of Toronto, Toronto, ON, Canada, Aboubakar Mounchili, DVM, MSc, PhD, Surveillance and Epidemiology, Public Health Agency of Canada, Ottawa, ON, Canada, Michael Mulvey, PhD, National Microbiology Laboratory, Winnipeg, MB, Canada, Stephanie Smith, MD, MSc, Division of Infectious Diseases, University of Alberta, Edmonton, AB, Canada, Karl Weiss, MD, MSc, FRCPC, H˘pital Maisonneuve-Rosemont, Montreal, QC, Canada and Canadian Nosocomial Infection Surveillance Program


G. Golding, None

A. E. Simor, Pfizer canada Inc: Investigator and Scientific Advisor, Research grant and Speaker honorarium

L. Pelude, None

E. Bryce, None

C. Frenette, None

K. Katz, None

M. Loeb, None

A. McGeer, None

A. Mounchili, None

M. Mulvey, None

S. Smith, None

K. Weiss, None

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