[1] Occupat Hlth & Safety Agcy Healthcare British Col, Vancouver, BC V6H 3X5, Canada
[2] Univ Manitoba, Fac Med, Dept Community Hlth Sci, Winnipeg, MB, Canada
[3] Univ British Columbia, Inst Hlth Promot Res, Vancouver, BC V5Z 1M9, Canada
[4] Univ British Columbia, Fac Med, Dept Hlth Care & Epidemiol, Vancouver, BC V5Z 1M9, Canada