[1] Royal Coll Surg Ireland, Dept Clin Pharmacol, Dublin 2, Ireland
[2] Royal Coll Surg Ireland, Dept Epidemiol, Dublin 2, Ireland
[3] St Vincents Hosp, Dept Pathol, Dublin 4, Ireland
[4] St Vincents Hosp, Dept Gastroenterol, Dublin 4, Ireland
[5] Beaumont Hosp, Dept Gastroenterol, Dublin 9, Ireland