1. Department of Clinical Science University of Bergen Bergen Norway
2. Department of Occupational Medicine Haukeland University Hospital Bergen Norway
3. Faculty of Medicine University of Bergen Bergen Norway
4. Department of Allergy, Respiratory Medicine and Sleep Landspitali University Hospital Reykjavik Iceland
5. Department of Sleep Landspitali University Hospital Reykjavik Iceland
6. University of Iceland Faculty of Medicine Reykjavik Iceland
7. Department of Public Health Environment Occupation and Health Danish Ramazzini Centre Aarhus University Aarhus Denmark
8. National Research Centre for the Working Environment Copenhagen Denmark
9. Department of Medical Sciences: Respiratory Allergy and Sleep Research Uppsala University Uppsala Sweden