1. Division of Virology, Department of Infection and Immunity, Jichi Medical University School of Medicine, Tochigi 329-0498, Japan
2. Department of Gastroenterology, National Hospital Organization Takasaki General Medical Center, Gunma 370-0829, Japan
3. Department of Gastroenterology and Hepatology, Kusunoki Hospital, Gunma 375-0024, Japan