1 Division of Gastroenterology and Hepatology, Johns Hopkins Medical Institutions, Baltimore, Maryland.
2 Clinical and Translational Epidemiology Unit, Massachusetts General Hospital and Harvard Medical School and Division of Gastroenterology, Massachusetts General Hospital and Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School and Department of Immunology and Infectious Diseases, Harvard T.H. Chan School of Public Health, Boston, Massachusetts. Electronic address: achan@mgh.harvard.edu.