1 Department of Emergency Medicine, St Paul's Hospital and the University of British Columbia, Vancouver, British Columbia, Canada; Center for Health Outcomes and Evaluative Sciences, St Paul's Hospital, Vancouver, British Columbia, Canada.
2 Department of Emergency Medicine, St Paul's Hospital and the University of British Columbia, Vancouver, British Columbia, Canada.
3 Department of Emergency Medicine, Vancouver General Hospital and the University of British Columbia, Vancouver, British Columbia, Canada.
4 School of Population and Public Health, University of British Columbia, Vancouver, British Columbia; Center for Disease Control, Province of British Columbia, Vancouver, British Columbia.