C.M., a 25-year-old female college student, has had episodic, watery diarrhea and colicky abdominal pain relieved by defecation for the past 9 months. Eight weeks before admission, the diarrhea increased to 3 to 5 semiformed stools daily. The frequency of the stools gradually increased to 5 to 10 times a day 1 week ago. At that time, C.M. noted bright red blood in the stools. Stool frequency has now increased to 10 to 15 per day, although the volume of each stool is estimated to be only “one-half cupful.” She feels a great urgency to defecate, even though the volume is small. She has not traveled outside the United States, has not been camping, and has not taken any antibiotics within the past 6 months. She has no known medication allergies, and takes only occasional over-the-counter acetaminophen for body aches or headaches. C.M. complains of anorexia and a 10-pound weight loss during the past 2 months. For the past 4 months, she has had intermittent swelling, warmth, and tenderness of the
