1. a Center for International Health and Development , Boston University , Boston , US
2. b Department of International Health , Boston University School of Public Health , Boston , US
3. c Infectious Diseases Section, Department of Medicine , Boston University School of Medicine , Boston , US
4. d Department of STDs and Dermatology , Ditan Hospital , Beijing , China
5. e Horizon Research Group , Beijing , China
6. f Consultant , Boston University School of Public Health , Boston , US
7. g Institute for Clinical Research and Health Policy Studies , Tufts-New England Medical Center , Boston , US