1. Gastroenterology and Endoscopy Unit, Fondazione IRCCS Policlinico San Matteo, 27100 Pavia, Italy
2. Specialization School of Diseases of Digestive System Pavia, University of Pavia, 27100 Pavia, Italy
3. Digestive Endoscopy Unit, Hospital Nacional Zacamil, San Salvador 01120, El Salvador