1. Department of Surgery, Johns Hopkins University School of Medicine, Baltimore, Maryland
2. Department of Surgery, Walter Reed National Military Medical Center, Bethesda, Maryland
3. Division of Gastroenterology and Hepatology, Johns Hopkins University School of Medicine, Baltimore, Maryland
4. Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, Maryland
5. Department of Epidemiology, Johns Hopkins School of Public Health, Baltimore, Maryland