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Last updated: June 24, 2021

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Diarrheal diseases are very common and, in most cases, self-limiting. Diarrhea is defined either as the presence of more than three bowel movements per day, water content exceeding 75%, or a stool quantity of at least 200–250 g per day. Acute diarrhea lasts for no longer than 14 days and is typically caused by viral or bacterial infection or food poisoning. Chronic diarrhea is often caused by underlying gastrointestinal or endocrinological conditions, such as inflammatory bowel disease or hyperthyroidism. Further symptoms may include fever, bloody stools, abdominal pain, and nausea and vomiting in cases of gastroenteritis. Diagnostic tests for acute diarrhea are usually unnecessary, but they may include CBC, stool samples, or colonoscopy for severe or chronic cases. Most cases of diarrhea only require symptomatic treatment, such as oral rehydration, while severe cases may necessitate administration of antibiotics and hospitalization for IV fluid replacement.

  • Diarrhea is present if one of the following criteria is fulfilled: [1][2]
    1. Frequent defecation: ≥ 3 times per day
    2. Altered stool consistency: increased water content
    3. Increase in stool quantity: more than 200–250 g per day
  • Acute diarrhea: lasting ≤ 14 days
  • Persistent diarrhea: lasting > 14 days
  • Chronic diarrhea: lasting > 30 days

Overview of pathogens causing watery and bloody diarrhea

Type of diarrhea Pathogen Pathogen characteristics Associated disorders
Watery diarrhea
  • Travelers’ diarrhea
  • Straight or curved (comma-shaped)
  • Cholera toxin (enterotoxin): “rice-water” diarrhea
  • Transmission via contaminated water or uncooked seafood (e.g., raw shellfish)
  • Transmission via ingestion of contaminated water (e.g., lakes, rivers, ponds, swimming pools)
  • Most commonly affects hikers or campers
Bloody diarrhea
  • Curved or spiral‑shaped with polar flagellum
  • Grows best at 37–42°C
  • No lactose fermentation
  • Flagellar motility
  • Hosts: humans, animals, and animal products (e.g., reptiles, poultry, pets, eggs)
  • Slow/absent lactose fermentation
  • Shiga toxin
  • Low infectious dose required (low ID50)
  • Humans are the only host.
  • Reservoir: contaminated pork and milk products

Infectious causes [1][3]

Noninfectious [5][6][7]

Disease transmission and risk factors [1]

  • Fecal-oral transmission
    • Ingestion of contaminated food or beverages (see “Traveler's diarrhea”)
    • Direct contact with contaminated surfaces or objects (e.g., touching bathroom surfaces or diapers and then touching mouth, nose, or eyes, or handling food without washing hands)
    • Direct contact with a sick individual (e.g., shaking hands, sharing food)
  • Risk factors
    • Daycare attendance, nursing home residency, hospitalization
    • Poor hygiene
    • Animal exposure
Pathophysiology [1] Associated disorders [3][8]
Exudative-inflammatory diarrhea
  • Damage to the intestinal mucosa may cause cytokine-induced water hypersecretion, impair absorption of osmotically active substances or fat, and/or disrupt water and electrolyte absorption.
  • Mucus, blood, and leukocytes present in stool
Secretory diarrhea
  • Active secretion of water into the intestinal lumen via inhibition/activation of enzymes (e.g., cAMP activity)
Osmotic diarrhea
  • Poor absorption or excessive ingestion of hydrophilic substances (e.g., salts and sugars, laxatives) causes water to be drawn into the intestinal lumen.
Motor diarrhea
  • Rapid intestinal passage due to increased bowel movements

The loss of bicarbonate-rich fluid in severe diarrhea may cause nonanion gap metabolic acidosis.

Traveler's diarrhea [10]

Factitious diarrhea

Laxative abuse

The workup for diarrhea includes a detailed patient history (e.g., recent travel), physical examination, and laboratory tests to assess severe cases.

Laboratory tests

Laboratory tests are usually not required in acute cases and are instead reserved for the diagnosis of severe or chronic disease.

Stool osmotic gap overview

Low osmotic gap High osmotic gap
Osmotic gap
  • < 50 mOsm/Kg
  • > 100 mOsm/Kg
  • Osmotic diarrhea (osmotic pull of ingested substances draws water into the intestinal lumen)


Because most cases of acute diarrhea are self-limited, symptomatic treatment is most common, focusing on oral rehydration. Therapy rarely involves medication.

  • Rehydration (especially important in children)
    • Mild to moderate dehydration: oral rehydration therapy with electrolyte-containing fluids, e.g., apple juice or oral rehydration solution
    • Severe cases: consider hospitalization; hydration with IV 0.9% sodium chloride
  • Antidiarrheal agents (e.g., loperamide)
    • Indicated in mild to moderate cases
    • Should be avoided if there is fever or blood in stools (indicative of systemic disease)
    • Loperamide is the best initial treatment for chemotherapy-induced diarrhea.
  • Antibiotics: are generally not indicated
  • Other: treatment of the underlying condition in the case of chronic diarrhea
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  2. Travelers' Diarrhea. Updated: July 10, 2015. Accessed: March 1, 2017.
  3. Kasper DL, Fauci AS, Hauser SL, Longo DL, Lameson JL, Loscalzo J. Harrison's Principles of Internal Medicine. McGraw-Hill Education ; 2015
  4. Walker HK, Hall WD, Hurst WJ, Silverman ME, Morrison G. Clinical Methods: The History, Physical, and Laboratory Examinations. Butterworths ; 1990
  5. Qiu FZ, Shen XX, Li GX, et al. Adenovirus associated with acute diarrhea: a case-control study.. BMC Infect Dis. 2018; 18 (1): p.450. doi: 10.1186/s12879-018-3340-1 . | Open in Read by QxMD
  6. Histamine Toxicity. Updated: March 1, 2017. Accessed: March 1, 2017.
  7. Overview of Food Poisoning. Updated: March 1, 2017. Accessed: March 1, 2017.
  8. Juckett G, Trivedi R. Evaluation of Chronic Diarrhea. Am Fam Physician. 2011; 84 (10): p.1119-1126.
  9. Diarrhoeal disease. Updated: April 1, 2013. Accessed: March 1, 2017.
  10. Diarrhea. Updated: March 1, 2016. Accessed: March 1, 2017.
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  14. Le T, Bhushan V, Bagga HS. First Aid for the USMLE Step 2 CK. McGraw-Hill Medical ; 2009
  15. Guandalini S. Diarrhea. Diarrhea. New York, NY: WebMD. Updated: November 11, 2016. Accessed: February 19, 2017.
  16. Diarrhoea. Updated: March 1, 2017. Accessed: March 1, 2017.
  17. Wald A. Factitious diarrhea: Clinical manifestations, diagnosis, and management. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. updated: September 16, 2015. Accessed: March 1, 2017.