A 65-year-old man goes to his general practitioner (GP) complaining of diarrhea. This had developed suddenly 2 days previously. His motions are watery and foul-smelling. There is no blood or mucus in the stool. There is a colicky abdominal pain not relieved by defecation. The man has a poor appetite and feels nauseated. He feels tired. The man has recently retired and returned 2 weeks ago from a coach trip.

No one else on the coach was ill during the holiday. He is otherwise well, with no significant medical history. He smokes 10 cigarettes a day and drinks two pints of beer a day. The examination is unremarkable, and the GP diagnoses ‘traveler’s diarrhea’, and prescribes loperamide. Two weeks later the patient returns with the problem. Diarrhea has persisted, and the patient has lost 6 kg in weight. Examination On examination, the patient looks well. His blood pressure is 158/88 mmHg.…