[1] Akershus Univ Hosp, Dept Infect Dis, Lorenskog, Norway
[2] Oslo Univ Hosp, Dept Gastroenterol, Oslo, Norway
[3] ProLAR Nett, Sogne, Norway
[4] Lovisenberg Diaconal Hosp, Unger Vetlesen Inst, Oslo, Norway
[5] Innlandet Hosp Trust, Norwegian Natl Advisory Unit Concurrent Subst Abu, Brumunddal, Norway
[6] Norwegian Directorate Hlth, Oslo, Norway
[7] Univ Oslo, Inst Clin Med, Oslo, Norway