[1] Sahlgrens Univ Hosp, Dept Occupat & Environm Med, S-41266 Gothenburg, Sweden
[2] Sahlgrens Univ Hosp, Dept Resp Med & Allergol, S-41266 Gothenburg, Sweden
[3] Univ Calif San Francisco, Div Environm & Occupat Med, Dept Med, San Francisco, CA 94143 USA
[4] Univ Calif San Francisco, Div Environm & Occupat Med, Inst Cardiovasc Res, San Francisco, CA 94143 USA
[5] Akad Sjukhuset, Dept Lung Med, Uppsala, Sweden
[6] Akad Sjukhuset, Dept Med Sci Occupat & Environm Med, Uppsala, Sweden
[7] Univ Hosp, Dept Resp Med & Allergol, Umea, Sweden