Hideaki Kato1, Takashi Ohya2, Yasuhiro Arai3, Keiichi Nakagawa4. 1. Infection Prevention and Control Department, Yokohama City University Hospital. 2. Department of Oral and Maxillofacial Surgery, Yokohama City University Graduate School of Medicine. 3. Department of Otolaryngology, Head and Neck Surgery, Yokohama City University School of Medicine. 4. Department of Bioengineering, Department of Precision Engineering, The University of Tokyo.