1. Department of Epidemiology and Biostatistics, School of Public HealthXi'an Jiaotong University Health Science Center Xi'an China
2. Department of Health ProfessionsHofstra University Hempstead New York
3. Department of Sexually Transmitted Disease Prevention and ControlXi'an Centers for Disease Control and Prevention Xi'an China
4. Department of HIV Testing MobilizationXi'an Center for Marie Stopes International Xi'an China