1. Department of Human Ecology; Graduate School of Medicine, The University of Tokyo; Bunkyo-Ku Tokyo 113-0033 Japan
2. Department of Sociology, Stockholm Center for Health and Social Change (Scohost); Södertörn University; Huddinge 141 89 Sweden
3. Hainan Provincial Center for Disease Control and Prevention; Haikou Hainan 57023 China