1. College of Public Health, North China University of Science and Technology, Tangshan, China.
2. Department of AIDS Research, Hebei Provincial Center for Disease Control and Prevention, Shijiazhuang, China.
3. College of Public Health, Hebei Medical University, Shijiazhuang, China.
4. Hebei Key Laboratory of Pathogen and Epidemiology of Infectious Disease, Hebei Provincial Center for Disease Control and Prevention, Shijiazhuang, China.