1. Section of Gastroenterology and Hepatology, Department of Medicine, Baylor College of Medicine , Houston, Texas , USA
2. Division of Abdominal Transplantation, Department of Surgery, Baylor College of Medicine , Houston, Texas , USA
3. Division of Gastroenterology, Duke University Medical Center , Durham, North Carolina , USA
4. VA Cooperative Studies Program Epidemiology Center-Durham and Durham VA Health Care System , Durham, North Carolina , USA
5. Division of Infectious Diseases, Department of Medicine, Oregon Health and Science University , Portland, Oregon , USA
6. VA Portland Health Care System , Portland, Oregon , USA
7. VA Puget Sound Health Care System , Seattle, Washington , USA
8. Department of Health Services, University of Washington School of Public Health , Seattle, Washington , USA
9. Division of General Internal Medicine, University of Washington School of Medicine , Seattle, Washington , USA