1. Division of Gastroenterology, Department of Internal Medicine, Severance Hospital, Institute of Gastroenterology, Yonsei University College of Medicine, Seoul, Korea
2. Division of Gastroenterology, Department of Internal Medicine, Incheon St. Mary's Hospital, The Catholic University of Korea College of Medicine, Seoul, Korea
3. Department of Internal Medicine, Hanyang University Guri Hospital, Hanyang University College of Medicine, Seoul, Korea