1. School of Public Health, Guangxi Medical University, Nanning, Guangxi, China
2. Department of Medicine, Boston Medical Center, Boston University Medical Campus, Boston, MA 02118, USA
3. Department of Community Medicine, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong
4. School of Nursing, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong