1. Public Health Ontario, Toronto, Ontario, Canada
2. ICES, Toronto, Ontario, Canada
3. Environmental Health Science and Research Bureau, Population Studies Division, and
4. Department of Family and Community Medicine and
5. Centre for Vaccine Preventable Diseases
6. Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada
7. College of Public Health and Human Studies, Oregon State University, Corvallis, Oregon
8. Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada
9. Department of Energy, Environmental, and Chemical Engineering, Washington University in St. Louis, St. Louis, Missouri
10. Air Health Science Division, Health Canada, Ottawa, Ontario, Canada
11. School of Epidemiology and Public Health, University of Ottawa, Ottawa, Ontario, Canada; and
12. Department of Epidemiology, Biostatistics, and Occupational Health, McGill University, Montreal, Quebec, Canada