A 43-year-old woman comes to the office due to 2 days of frequent "runny stools." She has not noticed blood or mucus in her stool but has had nausea, abdominal cramping, and malaise. Yesterday, the patient returned from a week-long vacation in Honduras, where she saw notable sights, snorkeled in the Caribbean Sea, and ate food from street vendors. Her medical history is significant for obesity, hypercholesterolemia, and gastroesophageal reflux disease. The patient takes atorvastatin and omeprazole and has not recently used antibiotics. She does not smoke tobacco or drink alcohol. Temperature is 37.8 C (100 F), blood pressure is 130/80 mm Hg, pulse is 80/min, and respirations are 12/min. BMI is 31 kg/m². The patient appears uncomfortable. The abdomen is soft and mildly tender but no guarding, rigidity, or rebound tenderness is present. The remainder of the physical examination is normal. Laboratory results are as follows: Which of the following pathogens is the most likely cause of this patient's symptoms?

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Explanation: 11ec2b69_bf85_3099_8f63_13bb5ef4883b_MD0005_00 Travelers' diarrhea is common in those who travel from resource-rich to resource-limited countries, occurring at rates as high as 50%. The vast majority of cases are bacterial in etiology, and the leading cause is enterotoxigenic Escherichia coli (ETEC). ETEC is transmitted via contaminated water or food and releases enterotoxins in the intestine that cause watery diarrhea and crampy abdominal pain 1-3 days after inoculation. Fever, nausea, vomiting, and myalgias may also occur. Infections are typically self-limited and resolve with supportive therapy in 3-4 days. Travelers to developing countries can reduce their risk of ETEC infection by avoiding peeled, uncooked fruits and vegetables; unpasteurized dairy products; food from street vendors; and untreated water (including ice). (Choice B) Giardia lamblia is a common protozoal cause of travelers' diarrhea that can manifest with watery diarrhea, malaise, and abdominal cramps. However, stools are typically foul-smelling or fatty, and symptoms almost always arise >1 week after exposure. (Choice C) Rotavirus is the most common viral cause of travelers' diarrhea and typically manifests with vomiting, nonbloody diarrhea, and fever. Bacterial causes are far more common, and this patient has no vomiting or significant fever. (Choice D) Shigella is a bacterial cause of travelers' diarrhea that typically results in dysentery (bloody, mucoid diarrhea) and high fever (unlike this patient). (Choice E) Vibrio parahaemolyticus is a bacterial cause of seafood-associated diarrhea that can manifest with watery or bloody diarrhea, abdominal cramps, nausea, vomiting, and fever. This patient has no fever, vomiting, or bloody stools. Educational objective: Enterotoxigenic Escherichia coli is the most common cause of travelers' diarrhea and typically manifests 1-3 days after exposure with watery diarrhea and crampy abdominal pain. Symptoms are usually self-limited and resolve spontaneously within 3-4 days.

A 43-Year-Old Woman Comes to the Office Due to 2