[1] Bristol Childrens Hosp, Dept Gastroenterol, Bristol B52 8BJ, Avon, England
[2] Univ Nottingham, Sch Med, Queens Med Ctr, Dept Epidemiol & Publ Hlth, Nottingham, England
[3] Univ Wales Hosp, Dept Child Hlth, Cardiff CF4 4XW, S Glam, Wales
[4] Childrens Hosp, Inst Child Hlth, Sheffield S10 2TH, S Yorkshire, England
[5] British Soc Gastroenterol, Res Unit, London, England
[6] British Paediat Surveillance Unit, London, England