P Ks Chan1, J Sy Chor2, A C Vlantis3, T L Chow4, S C Fung5, C H Lau6, F Yh Ng7, C S Wong2. 1. Department of Microbiology, The Chinese University of Hong Kong. 2. School of Public Health and Primary Care, The Chinese University of Hong Kong. 3. Department of Otorhinolaryngology, Head and Neck Surgery, The Chinese University of Hong Kong. 4. Head and Neck Division, Department of Surgery, United Christian Hospital. 5. Department of Dentistry and Maxillofacial Surgery, United Christian Hospital. 6. Department of Surgery, Queen Elizabeth Hospital. 7. Department of Surgery, Kwong Wah Hospital.