1. Clinical Medicine Research Unit, Medical Research Center University of Oulu Oulu Finland
2. Department of Otorhinolaryngology—Head and Neck Surgery Oulu University Hospital Oulu Finland
3. Department of Pediatrics and Adolescent Medicine Oulu University Hospital Oulu Finland
4. Tampere Center for Child Adolescent and Maternal Health Research Tampere Finland
5. Department of Otorhinolaryngology—Head and Neck Surgery Turku University Hospital Turku Finland
6. Department of Otorhinolaryngology, Faculty of Medicine University of Turku Turku Finland
7. Department of Pediatrics University of Eastern Finland and Kuopio University Hospital Kuopio Finland