1. Department of Gastroenterology, Østfold Hospital Trust, 1603 Fredrikstad, Norway
2. Department of Health Sciences, Østfold University College, K.G. Meldahlsvei 9, 1671 Kråkerøy, Norway
3. Department of Research, Telemark Hospital Trust, 3710 Skien, Norway
4. Institute of Clinical Medicine, University of Oslo-Oslo University Hospital, 0450 Oslo, Norway