1. School of Public Health, Xi’an Jiaotong University, Health Science Center, Xi’an, Shaanxi, PR China
2. Shenzhen Institute, Xi’an Jiaotong University, Shenzhen, Guangdong, PR China
3. Central Clinical School, Faculty of Medicine, Nursing and Health Sciences, Monash University, Melbourne, VIC, Australia
4. Melbourne Sexual Health Centre, Alfred Health, Melbourne, VIC, Australia
5. Department of Epidemiology and Biostatistics, College of Public health, Zhengzhou University, Zhengzhou, Henan Province, China