1. Division of Infectious Diseases, Department of Internal Medicine, Yonsei University College of Medicine, Seoul, Korea.
2. Division of Gastroenterology, Department of Internal Medicine, Yonsei University College of Medicine, Seoul, Korea.
3. Department of Laboratory Medicine, Yonsei University College of Medicine, Seoul, Korea.
4. Korea Institute of Geoscience and Mineral Resources, Daejeon, Korea.