1. Department of Pathology, Children's Hospital and Harvard Medical School,
2. Combined Program in Pediatric Gastroenterology, Children's Hospital, and Department of Pediatrics, Harvard Medical School, and
3. Division of Gastroenterology, Brigham and Women's Hospital, and Department of Medicine, Harvard Medical School, Boston, Massachusetts 02115;
4. Harvard Digestive Diseases Center, Boston, Massachusetts 02115
5. Department of Microbiology, University of Colorado Health Sciences Center, Denver, Colorado 80262; and