1. Department of General Practice, The Sixth Affiliated Hospital, Sun Yat-sen University , Guangzhou, Guangdong, P. R. China
2. Department of Gastroenterology, The Fifth Affiliated Hospital, Sun Yat-sen University , Zhuhai, Guangdong, P. R. China
3. Department of Gastrointestinal Endoscopy, The Sixth Affiliated Hospital, Sun Yat-sen University , Guangzhou, Guangdong, P. R. China
4. Department of Gastroenterology, The Sixth Affiliated Hospital, Sun Yat-sen University , Guangzhou, Guangdong, P. R. China