1 Gastroenterology, Medicine, Sepulveda Ambulatory Care Center, Veterans Affairs Greater Los Angeles Healthcare System, 111G, 16111 Plummer Street, North Hills, CA, 91343, USA. felix.leung@va.gov.
2 David Geffen School of Medicine at UCLA, Los Angeles, CA, USA. felix.leung@va.gov.
3 Gastroenterology, Medicine, Sepulveda Ambulatory Care Center, Veterans Affairs Greater Los Angeles Healthcare System, 111G, 16111 Plummer Street, North Hills, CA, 91343, USA.
4 David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.
5 Xijing Hospital of Digestive Diseases, Fourth Military Medical University, Xi'an, Shaanxi, China.