1. a Drug Treatment Program, British Columbia Centre for Excellence in HIV/AIDS , St. Paul's Hospital , Vancouver , BC , Canada
2. b Department of Medicine, Faculty of Medicine , University of British Columbia , Vancouver , BC , Canada
3. c Department of Medicine, Division of HIV/AIDS , University of California, San Francisco General Hospital , San Francisco , CA , USA
4. d Center for AIDS Prevention Studies , University of California , San Francisco , CA , USA
5. e Faculty of Health Sciences , Simon Fraser University , Burnaby , BC , Canada