1. Department of Public Health Sciences, University of Alberta and Institute of Health Economics, Edmonton, Alberta, Canada
2. GlaxoSmithKline Canada, Toronto, Ontario (formerly with Wyeth-Ayerst Canada, Inc), Canada
3. Aventis Canada, Toronto, Ontario, Canada
4. Department of Biostatistics, University of Toronto, Ontario, Canada
5. Division of Infectious Diseases, The Hospital for Sick Children and University of Toronto, Toronto, Ontario, Canada