1. Department of Epidemiology, School of Public Health, Cheeloo College of Medicine, Shandong University, Jinan, Shandong, China
2. Institution for AIDS/STD Control and Prevention, Shandong Center for Disease Control and Prevention, Jinan, Shandong, China
3. Department of AIDS/STD, Shandong Public Health Clinical Center, Jinan, Shandong, China