1. Section of Occupational and Environmental Medicine; University of Gothenburg; Gothenburg Sweden
2. Departmet of ENT, Head and Neck Surgery; Sahlgrenska Academy; Gothenburg University; Gothenburg Sweden
3. Lung Clinic; Tartu University Hospital; Tartu Estonia
4. Faculty of Medicine; Department of Respiratory Medicine and Sleep; Landspitali University Hospital; University of Iceland; Reykjavik Iceland
5. Department of Occupational Medicine; Haukeland University Hospital; Bergen Norway
6. Department of Medical Sciences: Respiratory Medicine and Allergology; Uppsala University; Akademiska sjukhuset; Uppsala Sweden
7. Division of Occupational and Environmental Medicine; Department of Public Health and Clinical Medicine; Umeå University; Umeå Sweden
8. Department of Public Health Section for Environment Occupation and Health; Aarhus University; Aarhus Denmark