1 Department of Paediatric and Adolescence Medicine, Copenhagen University Hospital - Amager and Hvidovre, Hvidovre, Denmark.
2 Copenhagen Centre for Inflammatory Bowel Disease in Children, Adolescents, and Adults, Copenhagen University Hospital - Amager and Hvidovre, Hvidovre, Denmark.
3 Department of Public Health, Section of Epidemiology, University of Copenhagen, Copenhagen, Denmark.
4 Departments of Epidemiology and Global Health, Boston University School of Public Health, Boston, Massachusetts, USA.
5 Department of Paediatrics and Adolescence Medicine, Copenhagen University Hospital - Rigshospitalet, Copenhagen, Denmark.