1. Department of Epidemiology, Harvard School of Public Health, 677 Huntington Avenue, Boston, MA 02115, USA.
2. Epidemiology and Disease Control Division, Ministry of Health, College of Medicine Building, 16 College Road, Singapore 169854.
3. Department of Medicine, University of Utah, Salt Lake City, UT 84132, USA.
4. Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Ontario L8N 3Z5, Canada.
5. City of Hamilton Public Health and Community Service Department, Hamilton, Ontario L8R 3L5, Canada.