Diarrhea, defined as three or more loose stools per day or more frequent stool passage than is normal for the individual, is a common disease with a monthly prevalence of around 5% in the United States. Acute diarrhea lasts 14 days or less and is almost always caused by an infectious agent, typically a virus. Testing is seldom required, as the disease tends to be self-limited and care is primarily supportive. Persistent diarrhea, lasting 15–30 days, is also typically caused by an infectious agent, but stool testing for pathogens is generally warranted to confirm the diagnosis. Chronic diarrhea, defined as diarrhea lasting longer than 30 days, has an extensive differential diagnosis. A thorough history followed by systematic stool and blood testing is required to identify the specific etiology. The presence of any red flags for severe or rapidly progressing diarrheal disease (e.g., sepsis, extreme dehydration, blood in the stool) mandates escalation of testing and, in some cases, . Ensuring adequate oral hydration, correcting dehydration, and providing symptomatic relief are fundamental components in the care of all patients with diarrhea. Curative treatment is directed toward the underlying cause.
The WHO defines diarrhea as ≥ 3 loose or watery stools per day or more frequent passage than is normal for the individual. 
For etiologies of acute, persistent, or chronic diarrhea, see specific subsections below.
Overview of pathogens causing watery and bloody diarrhea
|Type of diarrhea||Pathogen||Pathogen characteristics||Associated disorders|
|Watery diarrhea|| || |
| || |
|Bloody diarrhea|| |
| || |
| || || |
Infectious causes 
|Helminth infections|| |
Diarrhea is often classified as watery, fatty, and/or inflammatory to facilitate diagnosis and management. This classification scheme is most relevant for the.
|Classification of diarrhea by functional pathology |
|Fatty diarrhea|| |
|Watery diarrhea||Secretory diarrhea|| |
|Functional diarrheal disorders || |
Approach to diarrhea 
Detailed history and physical examination
- Exclude fecal incontinence and fecal impaction; see “Differential diagnoses of diarrhea.”
- Rule out medication-induced diarrhea and consider factitious diarrhea.
- Classify diarrhea:
- By duration of diarrheal illness: acute, persistent, or chronic
- By clinical presentation: watery, fatty, inflammatory
- Identify any red flags in diarrhea and risk factors for specific causes.
- Review medical and surgical history.
- Supportive care: Start oral hydration (or IV fluids) and offer symptom relief.
- Diagnostics: Obtain only when appropriate.
- Directed therapy: Consider empiric or targeted therapy (e.g., antibiotics) based on clinical presentation and study results.
Though most patients with diarrhea have mild symptoms and can be managed as outpatients, some patients may present with severe and even life-threatening symptoms that require hospitalization.
Antibiotics should only be utilized for specific indications.
Clinical assessment of diarrhea 
Key features of the disease presentation that facilitate efficient testing and prompt diagnosis include:
Duration of diarrheal illness
- Acute diarrhea: duration ≤ 14 days
- Persistent diarrhea: duration 15–30 days
- Chronic diarrhea: duration > 30 days
- Stool characteristics: watery, fatty, or bloody stools
- Associated symptoms
|Characteristic clinical features in diarrhea according to functional pathology|
|Loose, watery stools|| |
Risk factors for diarrhea
Assess for the presence of risk factors for specific etiologies, including:
- Recent travel : associated with
Occupational or recreational exposure
- May be associated with an infectious disease outbreak
- Potential routes of exposure include:
- Ingestion of contaminated food or beverages at a high-risk event (e.g., picnic, restaurant, buffet)
- Daycare (e.g., in a daycare attendee, family member of attendee, or daycare staff member)
- Direct contact with contaminated surfaces or objects
- Direct contact with an infected individual (e.g., shaking hands, sharing food)
- Animal contact
- Recent hospitalization: associated with (e.g., )
- Medication use
- Surgery 
- Radiation therapy: may cause secondary enterocolitis 
More than 700 medications can cause diarrhea and, therefore, the introduction of a new medication within 6–8 weeks of the onset of diarrhea should be considered as a potential cause. 
Red flags in diarrhea 
Acute or persistent diarrhea
- Symptoms of inflammatory diarrhea (dysentery)
- Patient characteristics that suggest an increased risk of severe disease
- > 48 hours duration without improvement
- Chronic diarrhea
General principles 
- Acute diarrhea
- Persistent diarrhea: Testing is usually limited to stool studies for infectious gastroenteritis.
- Testing is initially broad with advanced follow-up testing as indicated. 
- Repeat stool testing for infectious gastroenteritis.
Testing for diarrhea
For specific indications for testing, see the respective subsections below on acute, persistent, and chronic diarrhea.
- CBC: To evaluate for anemia, leukocytosis, and/or leukopenia
- CMP: Assessment of (e.g., electrolyte abnormalities, AKI) and/or liver disease
- CRP, ESR: Markers of inflammation
- Blood cultures: Identification of bacteremia
- Blood gases: Assessment of acid-base status
- Celiac disease serology: Initial testing for celiac disease
- Breath tests 
- CT abdomen or MRI abdomen: Identification of inflammation, structural disease, and/or ischemia 
- Endoscopic studies 
Endoscopic studies have limited diagnostic value in acute diarrhea but are commonly needed for the workup of chronic diarrhea to evaluate for the presence of inflammatory or neoplastic diseases. Their utility in persistent diarrhea is uncertain.
Stool diagnostic studies
- Stool culture: can be indicated if red flags in diarrhea are present (e.g., suspected invasive bacterial enteritis)
- Stool tests for CDI: if is suspected
|Stool diagnostic studies in diarrhea|
|Infectious diseases||Stool culture||Identification of infectious agents (e.g., in bacterial gastroenteritis)|
|Stool microscopy||Visualization of ova or parasites in the stool|
|Culture-independent methods (e.g., stool molecular diagnostic panels)||Identification of infectious agents in bacterial, viral, and protozoal gastroenteritis |
|Quantitative culture of small intestinal aspirate||Used to diagnose SIBO (gold standard test for bacterial overgrowth)|
|Stool tests for C. difficile infection (e.g., toxin test)||Identification of C. difficile infection|
|Inflammation||Stool microscopy||Visualization of fecal leukocytes|
|Fecal occult blood test (FOBT)||To screen for malignancy and mucosal inflammation|
|FIT DNA test||To screen for colonic cancer and adenomatous polyps|
|Fecal calprotectin and lactoferrin||Markers of inflammatory bowel disease (IBD)|
|Malabsorption||Sudan stain||Qualitative test for steatorrhea|
|72-hour quantitative fecal fat estimation||Quantitative test for steatorrhea|
|Fecal elastase-1||Confirmation of steatorrhea due to exocrine pancreatic insufficiency|
|Stool electrolytes (e.g., Na+, K+)||Used to calculate stool osmotic gap|
|Stool pH||Identification of carbohydrate malabsorption|
- Stool osmotic gap 
|Low stool osmotic gap||High stool osmotic gap|
|Osmotic gap|| || |
Therapy is guided byand .
- Mild to moderate dehydration: Start , e.g., use . 
- Severe cases
Early rehydration is especially important in children.
Antidiarrheal agents 
- Bismuth subsalicylate 
- Loperamide 
Racecadotril (not available in the US) 
- Enkephalinase inhibitor that reduces the hypersecretion of electrolytes and water into the intestinal lumen
- Appears to be well-tolerated and effective in bacterial diarrhea
Loperamide should be avoided in patients with suspected invasive diarrhea with inflammatory features, as it reduces intestinal motility, which consequently increases the risk of bacterial colonization and invasion. 
Acute or persistent diarrhea (≤ 30 days)
Approach to acute diarrhea (≤ 14 days) 
The management of acute diarrhea is primarily supportive, as the disease is usually a self-limited viral infection. Further management focuses on determining whether diagnostic testing and directed therapy are needed (e.g., antibiotic therapy for bacterial gastroenteritis). 
- Start hydration and offer symptom relief; see “Supportive care.”
- Determine whether the diarrhea is inflammatory (dysentery) or noninflammatory.
- Reserve stool diagnostic testing for pathogen identification (stool cultures with or without culture-independent methods) for specific scenarios 
- Consider empiric antibiotics for bacterial gastroenteritis after stool samples have been obtained. 
- Start targeted treatment based on the results; see also “ .”
If symptoms of an CT abdomen to identify ischemic, hemorrhagic, obstructive, and/or inflammatory diseases.  are present, consider an urgent
When indicated, stool studies in patients with acute diarrhea should include tests that can detect the presence of Salmonella, Shigella, Campylobacter, Yersinia, , and Shiga toxin-producing E. coli. 
Noninflammatory diarrhea (watery diarrhea) 
- Mild symptoms (e.g., daily activities of life are not affected)
- Moderate to severe symptoms (e.g., daily activities of life are affected)
- Severe symptoms, fever, or patients at risk for severe disease: Obtain stool studies for pathogen identification and targeted therapy.
Inflammatory diarrhea (dysentery) 
- No or low-grade fever: stool cultures or stool molecular testing
- Severe illness with fever
Approach to persistent diarrhea (15–30 days) 
- Review associated symptoms, history, and stool appearance.
- Obtain stool studies for pathogen identification (including parasites) in all patients.
- Avoid routine blood tests, imaging, and endoscopy in patients with a negative stool workup and no red flag symptoms.
- Offer empiric antibiotics to patients with suspected .
- Start targeted treatment based on diagnostic results; see also “ .”
In patients with prominent abdominal pain and/or bloody diarrhea, evaluate for , , and if stool testing does not indicate an infectious etiology.
Persistent diarrhea has a broader differential diagnosis than acute diarrhea. Parasitic infection (e.g., ), recurrent bacterial infection (e.g., ), and noninfectious causes (e.g., ) must be considered. 
Etiology of acute and persistent diarrhea 
|Etiology of acute and persistent diarrhea|
Chronic diarrhea (> 30 days)
Approach to chronic diarrhea
The differential diagnosis of chronic diarrhea is extensive. A systematic approach with efficient use of testing is needed to arrive at a diagnosis quickly. 
- Provide general supportive care.
- Assess for a possible health care-related etiology: e.g., medication-induced diarrhea
- Consider f . 
- Order initial diagnostics for chronic diarrhea.
- Consider a preliminary diagnosis of IBS-D if all of the following criteria are met: 
- Initial tests are normal.
- No red flags are present.
- are met.
- Consider further investigations: e.g., additional advanced tests, therapeutic trials
- Start directed therapy once a likely has been identified.
Chronic diarrhea can be classified as inflammatory, fatty, or watery. Grouping patients into broad categories based on clinical features and basic laboratory findings narrows the differential diagnosis and facilitates efficient advanced testing. 
is an intermediate diagnosis; it does not eliminate the possibility of another disease. Evaluation should continue if symptoms persist despite treatment for IBS-D. 
Etiology of chronic diarrhea 
Chronic diarrhea is commonly classified as watery, fatty, or inflammatory.
|Etiology of chronic diarrhea |
Initial diagnostics for chronic diarrhea 
Order initial studies. See also “Testing for diarrhea” in “Diagnostics.”
- Stool studies
- Blood tests: Obtain CRP levels , CBC, CMP, and . 
Imaging studies 
- Use imaging studies to evaluate and consider initially to rule out structural disease.
- Preferred modality: CT abdomen or MRI abdomen with enterography
Always test for Giardia infection in chronic diarrhea. 
Subsequent evaluation 
Perform guided diagnostics based onand the results of initial diagnostic testing.
|Diagnostic workup of patients with chronic diarrhea|
|Classification||Initial results||Further diagnostics|
|Fatty diarrhea || |
|Watery diarrhea ||Secretory diarrhea or functional diarrheal disorders|
Therapeutic trials 
- Consider if a diagnosis has not been established after a thorough evaluation.
- Consider if diagnostic tests for specific etiologies are not available.
- Examples of empiric therapies for specific causes 
- Involuntary release of stool, usually without a sensation of urgency
- May indicate abnormal neuromuscular function or anorectal structure
- Diagnosis is made based on history and a digital rectal examination.
- Impaction with fecal overflow (paradoxical diarrhea)
Subtypes and variants
Traveler's diarrhea 
- Definition: ≥ 3 unformed stools with at least one additional enteric symptom occurring after recent travel
- The highest rates occur after travel to Africa and South, Central, and West Asia.
- Approximately 25% of all travelers develop traveler's diarrhea.
- Enterotoxigenic E. coli (ETEC) is the most common cause of traveler's diarrhea globally.
- Campylobacter jejuni is the most common cause in Southeast Asia.
- Other pathogens
- Clinical features: exudative-inflammatory or secretory diarrhea, abdominal cramping, abdominal pain
- Antibiotics: Reserve for moderate to severe illness. 
- Supportive care 
- Postinfectious sequelae
Pharmacological prophylaxis 
Consider for travelers to high-risk areas (under specialist guidance); options include:
Bismuth subsalicylate (off label) 
- Consider for travelers with no contraindications for use.
- Should be taken with meals and at bedtime
- Antibiotic prophylaxis (generally discouraged) :
- Probiotics, prebiotics, and synbiotics are not recommended.
Factitious diarrhea 
- Definition: self-induced diarrhea, usually due to (often occurs in individuals with ), or dilution of stools with solutions
- Most prevalent in women
- Patients are usually health care professionals.
- History of multiple hospital admissions
- Clinical features: chronic diarrhea without an identifiable cause
- Laboratory tests: metabolic acidosis , metabolic alkalosis , hypokalemia, hypermagnesemia
- Stool osmolarity
- < 290 mOsm/L: indicates dilution of the stool with a hypotonic solution
- > 600 mOsm/L: indicates dilution of the stool with a hypertonic solution
- Laxative screen 
- Colonoscopy: may show in cases of anthraquinone abuse
- Types of laxative
- Osmotic diarrhea, meteorism
- Melanosis coli: benign hyperpigmentation of the colonic mucosa caused by anthraquinone abuse