1. Institut national de santé publique du Québec, Montreal, Quebec, Canada
2. University of Montreal Hospital Research Centre, Montreal, Quebec, Canada
3. Department of Social and Preventive Medicine, University of Montreal, Montreal, Quebec, Canada
4. Department of Obstetrics and Gynecology, University of Sherbrooke, Sherbrooke, Quebec, Canada
5. Department of Occupational and Environmental Health, University of Montreal, Montreal, Quebec, Canada
6. British Columbia Centre for Disease Control, Vancouver, British Columbia, Canada