1 Division of Gastroenterology, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan; Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan; Medicine Service, Ann Arbor Veterans Administration Health System, Ann Arbor, Michigan. Electronic address: [email protected].
2 Division of Gastroenterology, Department of Internal Medicine, San Francisco General Hospital, University of California San Francisco, San Francisco, California; University of California San Francisco School of Medicine, San Francisco, California. Electronic address: [email protected].