[1] Norwegian Univ Sci & Technol, Dept Publ Hlth & Gen Practice, HUNT Res Ctr, Levanger, Norway
[2] Haukeland Hosp, Ctr Clin Res, Bergen, Norway
[3] Univ Tromso, Dept Community Med, Tromso, Norway
[4] Hosp Sick Children, Resp Med, Toronto, ON, Canada
[5] Univ Oslo, Hosp RiksHosp, Dept Resp Med, Oslo, Norway
[6] Akershus Univ Hosp, Dept Pulm Med, Oslo, Norway
[7] Erasmus Univ, Med Ctr, Sophia Childrens Hosp, Dept Pulm Dis, Rotterdam, Netherlands
[8] Erasmus Univ, Med Ctr, Sophia Childrens Hosp, Dept Paediat,Div Resp Med, Rotterdam, Netherlands