[1] Orebro Univ Hosp, Dept Pediat, S-70185 Orebro, Sweden
[2] Karolinska Inst, Karolinska Univ Hosp, Dept Med, Clin Epidemiol Unit, Stockholm, Sweden
[3] Karolinska Inst, Karolinska Univ Hosp, Dept Gastroenterol & Hepatol, Stockholm, Sweden
[4] Harvard Univ, Sch Med, Boston, MA USA
[5] Orebro Univ Hosp, Clin Res Ctr, Orebro, Sweden