1. Department of Gastroenterology and Hepatology, Hokkaido University, Graduate School of Medicine, Sapporo, Japan;
2. Center for Gastroenterology, Teine Keijinkai Hospital, Sapporo, Japan;
3. Department of Gastroenterology, Tomakomai Municipal Hospital, Tomakomai, Japan;
4. Department of Gastroenterology, Steel Memorial Muroran Hospital, Muroran, Japan;
5. Department of Gastroenterology, Kitami Red Cross Hospital, Kitami, Japan;
6. Department of Gastroenterology, Iwamizawa Municipal General Hospital, Iwamizawa, Japan;
7. Department of Gastroenterology, Kushiro Rosai Hospital, Kushiro, Japan;
8. Department of Gastroenterology, NHO Hokkaido Medical Center, Sapporo, Japan;
9. Department of Gastroenterology, NTT East Sapporo Hospital, Sapporo, Japan;
10. Department of Gastroenterology, NHO Hakodate Hospital, Hakodate, Japan;
11. Department of Gastroenterology, KKR Tonan Hospital, Sapporo, Japan;
12. Department of Healthcare Epidemiology, School of Public Health in the Graduate School of Medicine, Kyoto University, Kyoto, Japan