- 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: 
- Frequent defecation: ≥ 3 times per day
- Altered stool consistency: increased water content
- 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 
|Helminth infections|| |
Risk factors and disease transmission 
- Transmission by direct contact and droplets
- Daycare attendance, nursing home residency, hospitalization
- Contaminated food and water (see “ ”)
- Animal exposure
|Pathophysiology ||Associated disorders |
|Secretory diarrhea|| || |
|Osmotic diarrhea|| |
|Motor diarrhea|| || |
The loss of bicarbonate-rich fluid in severe diarrhea may cause nonanion gap metabolic acidosis.
- Acute or chronic diarrhea (see “Definition” above)
- Further possible symptoms 
- Disease courses can range from mild to severe with need of hospitalization.
Traveler's diarrhea 
- Definition: infections which typically occur in patients with a history of recent travel
- Very common while traveling in Asian (“Delhi belly”), African, and Latin American countries ("Montezuma's Revenge")
- A major cause of diarrhea among children in developing countries
- Clinical features: exudative-inflammatory diarrhea or secretory diarrhea
- Definition: self-induced diarrhea, usually by (often occurs in individuals with )
- Most prevalent in women
- Patients are usually employed in the health field.
- History of multiple hospital admissions
- Clinical features: chronic watery diarrhea without an identifiable cause
- Osmotic diarrhea, meteorism
- Melanosis coli: benign hyperpigmentation of the colonic mucosa caused by anthraquinone abuse
Laboratory tests are usually not required in acute cases and are instead reserved for diagnosis of severe or chronic disease.
- 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.
- 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.
- Rehydration (especially in children)
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
- Other: treatment of the underlying condition in the case of chronic diarrhea