[1] Oita Univ, Fac Med, Dept Environm & Prevent Med, Yufu City, Oita 8795593, Japan
[2] Mongolian Natl Univ Med Sci, Dept Internal Med, Gastroenterol Unit, Ulaanbaatar 14210, Mongolia
[3] Cho Ray Hosp, Dept Endoscopy, Ho Chi Minh, Vietnam
[4] Baylor Coll Med, Dept Med, Gastroenterol & Hepatol Sect, Houston, TX 77030 USA