[1] Gradenigo Hosp, Dept Gastroenterol, Turin, Italy
[2] Univ Barcelona, Hosp Clin & Prov, Barcelona, Spain
[3] John Radcliffe Hosp, Dept Med, Oxford OX3 9DU, England
[4] Karolinska Inst, Huddinge Hosp, Dept Clin Immunol, S-10401 Stockholm, Sweden
[5] Karolinska Inst, Huddinge Hosp, Unit Gastroenterol & Hepatol, S-10401 Stockholm, Sweden
[6] Molinette Hosp, Dept Gastroenterol, Turin, Italy
[7] Univ Oslo, Natl Hosp, Epidemiol Sect, Oslo, Norway
[8] Univ Oslo, Natl Hosp, Dept Med, Inst Immunol, Oslo, Norway