Ease Into Prep with a USMLE^® Step 2 CK Question of the Day

The correct answer is C. Traveling abroad often entails abrupt changes in diet and climate, as well as exposure to conditions of poor sanitation, all of which results in a high incidence of diarrhea. This is self-limiting and manifests with watery diarrhea and dehydration, but no fever or other signs of systemic infection. The most frequent cause of traveler's diarrhea is enterotoxigenic Escherichia coli.

The remaining infectious agents listed here are all potential causes of noninflammatory diarrhea, which is not associated with blood and mucus in the stool, fever, systemic signs of infection, or fecal leukocytes.

Bacillus cereus (choice A), Clostridium perfringens (choice B), and Staphylococcus aureus (choice E), along with enterotoxigenic E. coli, are the most common agents associated with food poisoning due to production of toxins. All these pathogens produce a similar clinical picture of watery diarrhea, sometimes with nausea and vomiting, but no fever. The history is key in differentiating them. Without much of a history, expect the pathogen to be E. coli. If refried rice is part of the history, think B. cereus. If custards or picnic-like food enters the picture, as well as immediate post-meal diarrhea, think S. aureus. Finally, C. perfringens will often be tested less about food poisoning and more of its classic complication of gas gangrene in a diabetic foot.

Rotavirus (choice D) is one of the most important infectious causes of diarrhea in infants and young children in developing countries. It may also cause diarrhea in adults exposed to infected children.