1. Department of Clinical Microbiology, IIS-Fundación Jiménez Díaz, Madrid, Spain.
2. Otorhinolaryngology-Head and Neck Surgery, University of Helsinki and Helsinki University Hospital, Helsinki, Finland.
3. Department of Surgery, IIS-Fundación Jiménez Díaz, Madrid, Spain.
4. Department of Epidemiology, IIS-Fundación Jiménez Díaz, Madrid, Spain.