What are the causes of dysentery?

Causes of Dysentery

Dysentery is caused primarily by four bacterial pathogens—Shigella, Salmonella, Campylobacter, and Shiga toxin-producing E. coli (STEC)—along with the parasite Entamoeba histolytica, which must be considered especially in patients with travel to endemic areas. 1, 2

Primary Bacterial Causes

The four most important bacterial causes that should be included in every initial diagnostic workup for bloody diarrhea are:

• Shigella species remain a leading cause of dysentery worldwide, producing watery diarrhea that progresses to bloody stools with fever and tenesmus 3, 4
• Salmonella species cause inflammatory diarrhea with fever and bloody stools, and antimicrobial therapy may provide clinical benefit 1, 2
• Campylobacter species typically present with bloody diarrhea, severe abdominal pain, and minimal or no fever—a distinguishing clinical pattern 2, 3
• Shiga toxin-producing E. coli (STEC) causes severe abdominal pain with grossly bloody stools but characteristically without fever, which is a critical diagnostic clue 1, 2

Parasitic Causes

Amoebic dysentery caused by Entamoeba histolytica is a major consideration, particularly in developing countries:

• Amoebic colitis presents with bloody diarrhea, severe abdominal pain, and an indolent onset with minimal or absent fever—only 8% of patients have fever, which helps differentiate it from bacterial causes 2, 5
• This diagnosis should be suspected in patients with persistent diarrhea lasting 14 days or longer, especially with travel history to endemic areas 5, 3
• Microscopic examination of fresh stool (ideally within 15-30 minutes of passage) looking for motile trophozoites is essential for diagnosis 5, 6

Less Common Bacterial Causes

Several additional bacterial pathogens can cause dysentery in specific clinical contexts:

• Yersinia enterocolitica produces persistent abdominal pain, fever, and bloody stools; in children it can mimic appendicitis due to mesenteric adenitis 2, 3
• Non-cholera Vibrio species cause bloody diarrhea especially after exposure to salty or brackish water or consumption of raw/undercooked shellfish 2, 3
• Shigella dysenteriae type 1 can produce Shiga toxin and cause hemolytic-uremic syndrome (HUS), particularly in patients with international travel 1, 2
• Plesiomonas* species, Aeromonas species, enteroinvasive E. coli (EIEC), and *Balantidium coli are infrequent causes 2, 3, 7

Clinical Patterns to Guide Diagnosis

Use these clinical presentations to narrow your differential:

Fever + Bloody Diarrhea

• Prioritize testing for Salmonella, Shigella, Campylobacter, and Yersinia when fever accompanies bloody diarrhea, as antimicrobial therapy may provide clinical benefit 1, 2

Severe Abdominal Pain + Minimal/No Fever

• STEC should be the primary diagnostic consideration; both culture for O157:H7 and Shiga toxin assays for non-O157 strains are mandatory 1, 2
• STEC strains carrying the stx2 gene are associated with higher risk of both bloody diarrhea and HUS 1, 2

Bloody Diarrhea + Absent Fever

• Consider amoebic dysentery, especially with travel history or persistent symptoms; the paucity of fever contrasts sharply with bacterial causes 2, 5

Pathophysiologic Classification

Dysentery-causing organisms use two main mechanisms:

• Invasive organisms (Shigella, Salmonella, Campylobacter, E. histolytica, EIEC) invade the intestinal mucosa to induce acute inflammatory reaction with cytokine activation 7, 8
• Cytotoxin-producing, noninvasive bacteria (STEC, C. difficile) adhere to mucosa and release toxins that damage enterocytes and stimulate inflammatory mediators without direct invasion 8, 9

Critical Diagnostic Pitfalls

Avoid these common errors:

• Clostridioides difficile infection rarely produces bloody stools; the presence of blood should prompt evaluation for alternative or co-existing pathogens 2
• Do not assume viral gastroenteritis when blood and mucus are present—these findings indicate invasive bacterial colitis or amoebic dysentery, not viral infection 2
• The absence of fever does NOT rule out serious invasive disease, particularly with STEC or E. histolytica 2, 5
• Approximately 10% of patients with STEC who develop HUS do not have bloody diarrhea initially 1

Geographic and Epidemiologic Considerations

Tailor your differential based on exposure history:

• In industrialized countries, Shigella, Salmonella, Campylobacter, and STEC are most common 3
• In developing countries, E. histolytica must be considered, particularly in rural or periurban areas 3
• Travel to endemic areas (South/Southeast Asia, Central/South America, Africa) increases risk for Salmonella Typhi/Paratyphi, E. histolytica, and Shigella dysenteriae type 1 1, 2
• Seafood exposure raises suspicion for non-cholera Vibrio species 2, 3