• Clinical science



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


Infectious causes [1][3]

Parasitic Protozoan
Helminth infections

Noninfectious [5][6][7]

Foodborne toxins
Food poisoning

Risk factors and disease transmission [1]

  • Transmission by direct contact and droplets
  • Daycare attendance, nursing home residency, hospitalization
  • Contaminated food and water (see “Traveler's diarrhea”)
  • 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
  • Water is drawn into the intestinal lumen by poorly absorbed substances (e.g., salt, sugar, laxatives).
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.

Clinical features

  • Acute or chronic diarrhea (see “Definition” above)
  • Further possible symptoms [9]
  • Disease courses can range from mild to severe with need of hospitalization.

Subtypes and variants

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 diagnosis of severe or chronic disease.

  • Indications
  • Tests
    • CBC: may show anemia or leukocytosis
    • Stool samples
    • Stool culture: a test used to identify bacteria, viruses, fungi, or parasites in stool often in the context of a suspected gastrointestinal infection.
      • Stool cultures are not generally recommended, as the tests are expensive and have low sensitivity.
      • Indications: suspected invasive bacterial enteritis, severe illness, or fever (> 38.5°), required hospitalization, and/or stool tests positive for leukocytes/occult blood/lactoferrin
    • C. difficile toxin assay
    • Stool osmotic gap: an equation used to identify if watery diarrhea has an osmotic or secretory etiology



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