1. From the Department of Respiratory Medicine, Ghent University Hospital, Ghent, Belgium (G.G.B.); and the Departments of Epidemiology and Respiratory Medicine, Erasmus University Medical Center, Rotterdam (G.G.B.), and the Department of Pediatric Pulmonology and Pediatric Allergology, Beatrix Children’s Hospital, and the Groningen Research Institute for Asthma and COPD, University Medical Center Groningen, University of Groningen, Groningen (G.H.K.) — all in the Netherlands.