1. Department of Epidemiology and Environmental Health, Juntendo University School of Medicine, Tokyo,
2. Infectious Disease Surveillance Center, National Institute of Infectious Diseases, Tokyo,
3. First Department of Internal Medicine, Toho University School of Medicine, Tokyo,
4. First Department of Medicine, Hamamatsu University School of Medicine, Shizuoka and
5. Tokyo Orimono Health Insurance Society Clinic, Tokyo, Japan