[1] Sahlgrens Univ Hosp, Dept Resp Med & Allergol, Inst Med, SE-41345 Gothenburg, Sweden
[2] Univ Lund Hosp, Dept Resp Med, Lund, Sweden
[3] Orebro Univ Hosp, Dept Resp Med, Orebro, Sweden
[4] Gothenburg Univ, Sahlgrenska Acad, Inst Med, Hlth Care Res Unit, Gothenburg, Sweden