1. Department of Intensive Care Unit, The 305 Hospital of PLA, Beijing 100017, P.R. China
2. Department of General Medicine, Southwest Hospital, Third Military Medical University, Chongqing 400038, P.R. China
3. Center for Disease Control and Prevention of Central Theater Command, Beijing 100049, P.R. China
4. Department of General Surgery, Center for Minimally Invasive Gastrointestinal Surgery, Southwest Hospital, Third Military Medical University, Chongqing 400038, P.R. China