David S C Hui1,2, Nelson Lee1,3, Paul K S Chan2,4. 1. Department of Medicine and Therapeutics, The Chinese University of Hong Kong, Hong Kong, China. 2. Stanley Ho Center for Emerging Infectious Diseases, The Chinese University of Hong Kong, Hong Kong, China. 3. Division of Infectious Diseases, University of Alberta, Edmonton, Canada. 4. Department of Microbiology, The Chinese University of Hong Kong, Hong Kong, China.