[1] Ghent Univ Hosp, Dept Resp Med, Pintelaan 185, B-9000 Ghent, Belgium
[2] Univ Med Ctr Rotterdam, Erasmus MC, Dept Epidemiol, POB 2040, NL-3000 CA Rotterdam, Netherlands
[3] Franciscus Gasthuis, Dept Resp Med, NL-3045 PM Rotterdam, Netherlands
[4] Univ Med Ctr Rotterdam, Erasmus MC, Dept Resp Med, POB 2040, NL-3000 CA Rotterdam, Netherlands