1. Department of Environmental and Preventive Medicine, Oita University Faculty of Medicine, Yufu, Japan
2. The Gastroenterology Center, The First Central Hospital of Mongolia, Ulaanbaatar, Mongolia
3. Department of Gastroenterology, Mongolian National University of Medical Sciences, Ulaanbaatar, Mongolia
4. Endoscopy Unit, Mongolia-Japan Teaching Hospital, Mongolian National University of Medical Sciences, Ulaanbaatar, Mongolia
5. Department of Advanced Medical Sciences, Oita University Faculty of Medicine, Oita, Japan
6. Research Center for Global and Local Infectious Diseases (RCGLID), Oita University, Oita, Japan
7. Department of Medicine, Gastroenterology and Hepatology Section, Baylor College of Medicine, Houston, TX, USA