Wing-Wai Yew1, Kwok-Chiu Chang2, Denise P Chan1, Ying Zhang3. 1. Stanley Ho Centre for Emerging Infectious Diseases, The Chinese University of Hong Kong, Hong Kong, China. 2. Department of Health, Tuberculosis and Chest Service, Centre for Health Protection, Hong Kong, China. 3. Department of Molecular Microbiology and Immunology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD, USA.