1 Department of Paediatrics, Martini Hospital, Groningen, The Netherlands.
2 Department of Paediatric Pulmonology and Paediatric Allergology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
3 GRIAC Research Institute, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
4 Department of Epidemiology, Martini Hospital, Groningen, The Netherlands.