1. Department of Gastrointestinal Surgery, Haraldsplass Deaconess Hospital , Bergen , Norway
2. Department of Gastrointestinal Surgery, Haukeland University Hospital , Bergen , Norway
3. Department of Clinical Medicine, University of Bergen , Bergen , Norway
4. Centre for Clinical Research, Haukeland University Hospital , Bergen , Norway
5. Department of Global Public Health and Primary Care, University of Bergen , Bergen , Norway