[1] Univ Penn, Perelman Sch Med, Dept Med, Div Gastroenterol, Philadelphia, PA 19104 USA
[2] Univ Penn, Perelman Sch Med, Ctr Clin Epidemiol & Biostat, Philadelphia, PA 19104 USA
[3] Univ Penn, Perelman Sch Med, Philadelphia, PA 19104 USA
[4] Univ Autonoma Barcelona, Hosp Sant Pau, Dept Gastroenterol, E-08193 Barcelona, Spain
[5] Univ Penn, Perelman Sch Med, Dept Pathol, Philadelphia, PA 19104 USA
[6] Wilmott Ctr Endoscop Innovat Res & Training, Pittsburgh, PA USA