1. Azabu University, 1-17-71 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5201, Japan
2. Hokkaido Institute of Public Health, Kita 19, Nishi 12, Kita-ku, Sapporo, Hokkaido 060-0819, Japan
3. National Institute of Infectious Diseases, Toyama 1-23-1, Shinjuku-Ku, Tokyo 162-8640, Japan