1. Department of Pulmonary Diseases and Clinical Allergology, Turku University Hospital and University of Turku, Kiinamyllynkatu 13, 20520 Turku, Finland
2. Clinical Research Unit for Pulmonary Diseases and Division of Pulmonology, Helsinki University Central Hospital, Tukholmankatu 8C, 00290 Helsinki, Finland
3. Department of Pulmonology, University Medical Center Groningen, Hanzeplein 1, 9700 RB Groningen, The Netherlands
4. Department of Epidemiology, University Medical Center Groningen, Hanzeplein 1, 9700 RB Groningen, The Netherlands