Bloody diarrhea after a missionary trip in the Caribbean. Which organism is most likely?

• A. Giardia lamblia
• B. Shigella
• C. Campylobacter
• D. Entamoeba histolytica

Answer: (D)

Invasive intestinal infection acquired during travel to resource-limited regions is the key idea. Entamoeba histolytica is contracted by ingesting cysts in contaminated water or food. Once in the colon, it invades the mucosa and produces ulcers, leading to bloody, sometimes mucoid diarrhea. It can also spread to the liver and cause abscesses, a feature that helps distinguish it from other travel-related diarrheal pathogens. Diagnosis is often made by finding trophozoites in stool that may contain red blood cells, and treatment typically involves a tissue-active agent like metronidazole or tinidazole, followed by a luminal agent to eradicate cysts.

While other organisms can cause bloody diarrhea (for example, bacteria like Shigella or Campylobacter), the combination of a traveler’s exposure in a developing region and the classic presentation of invasive colitis with potential extraintestinal spread points most strongly to Entamoeba histolytica. Giardia causes nonbloody, fatty diarrhea and is noninvasive, making it less likely in this scenario.