1. Crohn’s and Colitis Center, Brigham and Women’s Hospital, Harvard Medical School , Boston, MA , USA
2. Harvard Medical School , Boston, MA , USA
3. Division of Gastroenterology, Brigham and Women’s Hospital, Harvard Medical School , Boston, MA , USA
4. Division of Gastroenterology, Tufts Medical Center, Tufts University School of Medicine , Boston, MA , USA
5. Center for Clinical Epidemiology, Odense University Hospital , Odense , Denmark