Pathogens That Cause Bloody Diarrhea
The primary pathogens causing bloody diarrhea are Shiga toxin-producing E. coli (STEC), Shigella, Salmonella, Campylobacter, Entamoeba histolytica, noncholera Vibrio species, Yersinia, Balantidium coli, and Plesiomonas. 1
Bacterial Pathogens
Most Common Invasive Bacteria
Shigella, Salmonella, Campylobacter, and STEC are the four most important bacterial causes of visible blood in stool and should be tested for when bloody diarrhea is present. 1, 2
Shiga toxin-producing E. coli (STEC) causes severe abdominal pain with grossly bloody stools, though patients typically present without fever—this absence of fever is a key distinguishing feature. 1, 2
Shigella species cause dysentery by invading the colonic mucosa, multiplying within epithelial cells, causing cell death and lateral spread that results in mucosal ulceration, inflammation, and bleeding. 3, 4
Campylobacter produces bloody diarrhea with severe abdominal pain and minimal or no fever in many cases. 1
Less Common Bacterial Causes
Yersinia enterocolitica causes persistent abdominal pain with fever and bloody stools, particularly in school-aged children where it can mimic appendicitis due to mesenteric adenitis. 1, 2
Noncholera Vibrio species can cause bloody diarrhea, especially with exposure to salty or brackish waters or consumption of raw/undercooked shellfish. 1, 2
Plesiomonas is a less common cause of visible blood in stool. 1
Parasitic Pathogens
Entamoeba histolytica (amoebic colitis) causes bloody diarrhea with a more indolent onset and is characterized by minimal or absent fever—only 8% of patients present with fever, which is the critical distinguishing feature from bacterial dysentery. 1, 2, 5
Balantidium coli is a rare parasitic cause of bloody diarrhea. 1
Clinical Context and Testing Priorities
When fever accompanies bloody diarrhea, prioritize testing for Salmonella, Shigella, Campylobacter, and Yersinia as these are the enteropathogens for which antimicrobial therapy may provide clinical benefit. 1
When bloody diarrhea occurs with severe abdominal pain but minimal or no fever, STEC should be the primary consideration, and both culture for O157:H7 and Shiga toxin detection for non-O157 strains must be performed. 1
Important Caveats
Clostridium difficile causes abdominal pain and diarrhea but bloody stools are NOT an expected manifestation of C. difficile infection—if blood is present, consider alternative or co-existing pathogens. 1
Shigella dysenteriae type 1 can produce Shiga toxin and should be considered as a cause of hemolytic uremic syndrome, especially in patients with international travel history. 1
STEC strains carrying stx2 genes are associated with increased risk of both bloody diarrhea and hemolytic uremic syndrome (HUS), making early identification critical. 1, 6
Amoebic dysentery requires a wet preparation of recently passed stool looking for motile trophozoites with ingested red blood cells to distinguish it from bacterial causes, as the absence of fever can lead to dangerous delays in diagnosis. 2, 5