A 65-year-old man comes to the emergency department due to abdominal pain and diarrhea. Three weeks ago, he drove from Texas to Mexico for a family vacation. Temperature is 38.3 C (101 F), blood pressure is 115/70 mm Hg, and pulse is 98/min. Abdominal examination shows mild, generalized tenderness with no rebound tenderness or guarding. Leukocyte count is 14,000/mm³. Sigmoidoscopy demonstrates white-yellow plaques on the colonic mucosa, and biopsy shows that the plaques are composed of fibrin and inflammatory cells. Further questioning regarding this patient's trip to Mexico is most likely to reveal which of the following events?

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11ec160b_3937_4f81_9249_5fade4fc9a5c_MD0001_00 This patient has abdominal pain, diarrhea, and leukocytosis. The formation of pseudomembranes (white-yellow plaques composed of fibrin, inflammatory cells, and cellular debris) on the colonic mucosa is highly consistent with pseudomembranous colitis due to Clostridium difficile, a spore-forming bacillus that colonizes up to 50% of hospitalized adults. Antibiotic therapy (eg, fluoroquinolones for bacterial pneumonia) increases the risk of C difficile infection as it kills intestinal microbes that normally keep potential pathogens in check. C difficile can proliferate in the altered microbiome, leading to overgrowth and clinical disease. C difficile produces 2 toxins-toxin A (enterotoxin) and toxin B (cytotoxin)-which penetrate colonic epithelial cells and damage cellular cytoskeletons and intercellular tight junctions. This results in widespread inflammation, edema, necrosis, and fibrin deposition. Clinical manifestations range from watery diarrhea and mild abdominal cramping to fulminant colitis with nonobstructive colonic enlargement (megacolon) and intestinal perforation. (Choices A and B) Ingestion of undercooked shellfish is associated with Vibrio, Norwalk virus, and hepatitis A infections. Traveler's diarrhea, caused by bacteria (eg, enterotoxigenic Escherichia coli, Campylobacter, Salmonella, Shigella) or parasites (eg, Giardia), is often due to contaminated water consumption. These conditions can manifest as diarrhea and abdominal pain; however, pseudomembranes are virtually pathognomonic for C difficile colitis. (Choice C) Consumption of undercooked pork is a risk factor for intestinal tapeworm (taeniasis), which occurs after ingestion of Taenia solium. Patients are often asymptomatic but may have nausea or abdominal pain. (Choice E) Adult botulism occurs after ingestion of preformed toxin in home-canned food. This neurotoxin inhibits acetylcholine release from the nerve terminals at neuromuscular junctions and causes a descending flaccid paralysis. Educational objective: Antibiotics disrupt the normal intestinal flora and which can allow for overgrowth of Clostridium difficile, an anaerobic, gram-positive, spore-forming bacillus. C difficile produces 2 toxins that penetrate colonic epithelial cells leading to watery diarrhea, abdominal cramping, and colitis. The presence of a pseudomembrane (exudate on colonic mucosa consisting of fibrin and inflammatory cells) is highly suggestive of C difficile infection.

A 65-Year-Old Man Comes to the Emergency Department Due to Abdominal