A 25-year-old woman presents to the physician after returning from a 10-day trip to Mexico. Two days after returning home, she developed watery diarrhea, abdominal cramping, and nausea. She denies fever, bloody stools, or severe abdominal pain. Past medical history is negative, and she does not take any medications. Temperature is 37.0°C (98.6°F), blood pressure is 118/72 mm Hg, pulse is 84/min, and respiratory rate is 14/min. Physical examination is unremarkable. She remains able to tolerate oral fluids.
Which of the following is the most likely causative organism?
The correct answer is:
B) Enterotoxigenic Escherichia coli
This patient has classic traveler’s diarrhea. The illness is characterized by acute watery diarrhea developing during or shortly after travel to a resource-limited region. Enterotoxigenic E. coli (ETEC) is the most common bacterial cause worldwide. The absence of fever, bloody stools, or severe systemic symptoms further supports a toxin-mediated noninvasive infection.
ETEC produces heat-labile and heat-stable enterotoxins that increase intestinal secretion of water and electrolytes. Most cases are self-limited and resolve within several days. Management primarily consists of oral hydration. Antibiotics may be considered in selected patients with moderate or severe symptoms, but supportive care remains the foundation of treatment.
Answer choice A: Entamoeba histolytica, is incorrect.
Amebic colitis often causes bloody diarrhea and may be associated with liver abscesses. It typically produces a more invasive clinical picture.
Answer choice C: Salmonella enterica, is incorrect.
Salmonella frequently causes inflammatory diarrhea associated with fever and may follow exposure to poultry, eggs, or reptiles.
Answer choice D: Shigella species, is incorrect.
Shigella commonly causes high fever, abdominal pain, and bloody diarrhea due to mucosal invasion.
Answer choice E: Vibrio vulnificus, is incorrect.
Vibrio vulnificus is associated with raw seafood exposure and severe infections, particularly in patients with chronic liver disease.
Key Learning Point
Enterotoxigenic E. coli is the most common cause of traveler’s diarrhea and typically produces self-limited watery diarrhea without invasive symptoms.
