1. Department of Gastroenterology, International University of Health and Welfare Hospital, Nasushiobara, Japan.
2. Division of Virology, Department of Infection and Immunity, Jichi Medical University, Shimotsuke, Japan.
3. Department of Pathology, International University of Health and Welfare Hospital, Nasushiobara, Japan.
4. Department of Otorhinolaryngology, International University of Health and Welfare, Narita Hospital, Narita, Japan.