• 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. Frequent defecation: ≥ three times per day
    2. Altered stool consistency: water content > 75%
    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

Parasitic Protozoan
Helminth infections


Foodborne toxins
Food poisoning
  • Aflatoxin
  • Histamine toxicity
  • Chemical contaminants (e.g., lead, cadmium, insecticides)
  • Tumor/stenotic processes → paradoxical diarrhea

Risk factors and disease transmission

  • Transmission by direct contact and droplets
  • Day care attendance, nursing home residency, hospitalization
  • Contaminated food and water (see traveler's diarrhea)
  • Animal exposure



Pathophysiology Associated disorders
Exudative-inflammatory diarrhea
  • Damage to the intestinal mucosa may cause cytokine-induced water hypersecretion, impair absorption of osmotically active substances or fat, 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 non-anion gap metabolic acidosis!


Clinical features

  • Acute or chronic diarrhea (see “Definition” above)
  • Further possible symptoms
    • Fever
    • Abdominal pain and cramping
    • Blood in stool
    • Nausea and vomiting in cases of gastroenteritis
    • Signs of dehydration in severe cases
    • Chronic cases: malnutrition and, in children, failure to thrive
  • Disease courses can range from mild to severe with need of hospitalization.


Subtypes and variants

Traveler's diarrhea

Factitious diarrhea

  • Definition: self-induced diarrhea, usually by laxative abuse; often occurs in individuals with factitious disorders
  • Epidemiology
    • Most prevalent in women
    • Patients are usually employed in the health field.
    • History of multiple hospital admissions
  • Clinical findings: chronic watery diarrhea without identifiable cause
  • Diagnosis
    • Laboratory tests: metabolic alkalosis, hypokalemia, hypermagnesemia
    • Colonoscopy: may show melanosis coli in cases of anthraquinone abuse
  • Treatment
    • Correction of electrolyte disturbances and dehydration
    • Referral to psychotherapy

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
    • Diarrhea lasting > 4 days
    • High fever
    • Blood in stools
    • Suspicion of IBD
    • Immunosuppression
  • Tests
    • CBC: may show anemia or leukocytosis
    • Stool samples: leukocytes; ova and parasites
    • Bacterial stool culture
      • Indications: suspicion of invasive bacterial enteritis, moderate to severe illness
    • C. difficile toxin assay


  • Colonoscopy: in patients with chronic diarrhea without identifiable cause
  • CT: if diverticulitis or IBD is suspected



Since most cases of acute diarrhea are self-limited, treatment is mostly symptomatic, focusing on oral rehydration, and rarely requires medication.

  • Rehydration (especially in children)
    • Mild to moderate dehydration: oral administration of electrolyte-containing fluids (e.g., apple juice or Pedialyte®)
    • Severe cases: consider hospitalization; hydration with IV sodium chloride at 0.9%
  • Antidiarrheal agents: (e.g., loperamide): may be given in mild to moderate cases; should be avoided if there is fever or blood in stools (indicative of systemic disease)
  • Antibiotics: are generally not indicated
  • Treatment of the underlying condition in cases of chronic diarrhea