A 29-year-old man comes to the emergency department with a 5-day history of diarrhea and abdominal pain. The diarrhea occurs 5 or 6 times a day; it was initially watery but has become bloody. The patient describes the pain as colicky and severe, with associated nausea and decreased appetite but no vomiting. Medical history is insignificant, with no prior episodes of similar symptoms and no recent hospitalizations or illnesses. The patient works as a digital marketing specialist and has not traveled outside the United States. Temperature is 36.6 C (97.9 F), blood pressure is 123/82 mm Hg, and pulse is 102/min. The patient has prominent periumbilical and right lower quadrant tenderness but no guarding or rebound. Rectal examination shows brown stool mixed with blood. Which of the following is the most likely etiology in this patient?
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Bloody diarrhea is most often caused by infectious gastroenteritis due to bacterial pathogens, specifically Shiga toxin–producing Escherichia coli (STEC), Shigella, or Campylobacter; other organisms that often cause watery stools (eg, Salmonella) can occasionally cause bloody stools. Of the given answer choices, STEC is the most likely diagnosis.
STEC transmission typically occurs via consumption of contaminated beef products, although outbreaks can occur in association with other foods such as fruits, leafy vegetables, and milk products. Isolated cases without a clear source are also common. The presentation classically involves inflammatory diarrhea with abdominal pain and stools that are initially watery but later contain blood. This patient's lack of fever is typical of infection with STEC; although a minority of patients with STEC gastroenteritis may have low-grade fever, the presence of a temperature >38.5 C (101.3 F) suggests an alternate diagnosis.
The diagnosis can be confirmed with multiplex nucleic acid amplification testing or assay for Shiga toxin in stool; stool culture should always be obtained for strain identification and outbreak tracing. Treatment is generally supportive (eg, aggressive fluid administration), and antibiotics should be avoided due to the increased risk for hemolytic uremic syndrome.
(Choice A) Clostridioides difficile–associated diarrhea presents as frequent, foul-smelling loose stools associated with prior antibiotic use or exposure to health care settings. Infection in a patient without these risk factors is uncommon, and bloody diarrhea is atypical.
(Choice B) Clostridium perfringens is a common cause of a toxin-mediated, food-borne illness (eg, contaminated, undercooked meat), leading to nonbloody diarrhea and abdominal pain. Symptoms typically resolve within 1-2 days, and this patient's bloody diarrhea is inconsistent with this infection.
(Choice D) Listeria monocytogenes is a rare cause of gastroenteritis that presents with watery diarrhea, in addition to a self-limited, flu-like illness (eg, fever, muscle/joint aches) lasting <3 days in immunocompetent patients. This patient's 5-day history and bloody stools would not be expected.
(Choice E) Rotavirus is a frequent cause of acute gastroenteritis, particularly in unvaccinated children. Although adults may have mild symptoms, nonbloody diarrhea is typical.
Educational objective:
Shiga toxin–producing Escherichia coli is a food-borne pathogen (eg, contaminated beef) that causes inflammatory diarrhea. Stools are initially watery but then become bloody. Most patients are afebrile, and high fever should raise suspicion for other pathogens.