1. a National Center for AIDS/STD Prevention and Control , China , CDC , China
2. b School of Public Health , University of California , Los Angeles , CA , USA
3. c Yunnan Center for Disease Prevention and Control , Yunnan , China
4. d Guangxi Center for Disease Prevention and Control , Guangxi , China
5. e School of Public Health , University of North Carolina , Chapel Hill , NC , USA
6. f Beijing Ditan Hospital , Beijing , China