1. Department of Pediatrics, Sapporo Medical University School of Medicine, Sapporo, Hokkaido, Japan
2. Department of Virology Ⅱ, National Institute of Infectious Diseases, Musashimurayama, Tokyo, Japan
3. Department of Pediatrics, Sunagawa City Hospital, Sunagawa, Hokkaido, Japan
4. Nihira Children's Clinic, Sapporo, Hokkaido, Japan
5. Graduate School of Health Science, Gunma Paz University, Takasaki, Gunma, Japan