1 Division of Gastroenterology and Hepatology, Graduate School of Medical and Dental Sciences, Niigata University, 1-757 Asahimachido-ri, Chuo-ku, Niigata 9518510, Japan.
2 Department of General Medicine, Niigata University School of Medicine, 1-757 Asahimachido-ri, Chuo-ku, Niigata 9518510, Japan.