[1] McMaster Univ, Fac Hlth Sci, Michael G DeGroote Sch Med, Firestone Inst Resp Hlth, Hamilton, ON, Canada
[2] Univ So Denmark, Dept Pediat, Kolding Hosp, Kolding, Denmark
[3] AstraZeneca Res & Dev, Lund, Sweden
[4] McGill Univ, Jewish Gen Hosp, Lady Davis Res Inst, Ctr Clin Epidemiol, Montreal, PQ H3T 1E2, Canada