1. Department of Microbiology; Yamagata Prefectural Institute of Public Health; Tokamachi 1-6-6; Yamagata; 990-0031; Japan
2. Department of Infectious Diseases; Yamagata University Faculty of Medicine; Iida-Nishi 2-2-2; Yamagata; 990-9585; Japan
3. Yamanobe Pediatric Clinic; Yamanobe 2908-14; Yamagata; 990-0301; Japan
4. Katsushima Pediatric Clinic; Minamidate 4-4-12; Yamagata; 990-2461; Japan
5. Virus Research Center, Sendai Medical Center; Sendai; 983-8520; Japan