1. Department of Infection Control Science, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, Tokyo, Japan
2. Department of Bacteriology, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, Tokyo, Japan
3. Tokyo Metropolitan Institute of Public Health, 3-24-1, Hyakunin-cho, Shinjuku-ku, Tokyo, Japan