Clinical Subject Page

Acute Diarrheal Disease

Acute Diarrheal Disease is characterized by the sudden onset of loose or watery stools, usually lasting less than 14 days. It is commonly caused by gastrointestinal infections, especially viruses and bacteria. The main immediate concern is dehydration and electrolyte loss, while severe cases may cause hypovolemic shock, Acute Kidney Injury (AKI), or sepsis

Also called

Acute diarrhea

ICD-10

R19.7

Specialty

Infectious

Onset

Acute

Reviewed

August 2026

On This Page

Overview

Overview
Etiology & Risk Factors

Etiology & Risk Factors
Pathophysiology

Pathophysiology
Clinical Presentation

Clinical Presentation
History Taking

History Taking
Physical Examination

Physical Examination
Investigations

Investigations
Diagnosis

Diagnosis
Management

Management
Complications

Complications
Prognosis

Prognosis
Key Points / Clinical Pearls

Key Points / Clinical Pearls

Overview

–Acute Diarrheal Disease may be infectious or non-infectious. Infectious causes include viruses, bacteria, and parasites, while non-infectious causes include medications, toxins, food intolerance, and other gastrointestinal disorders.

Common infectious causes include norovirus, rotavirus, Escherichia coli, Salmonella, Shigella, Campylobacter, and Vibrio cholerae

Teaching point The most important first step in Acute Diarrheal Disease is assessment of hydration and severity. Most uncomplicated cases require fluid and electrolyte replacement rather than antibiotics.

Etiology & Risk Factors

Acute Diarrhoeal Disease · Aetiology & Risk Factors

Definition

WHO criteria

≥3 loose/watery stools per day. Duration <14 days = acute. 14–30 days = persistent. >30 days = chronic.

Secretory

Toxin-mediated

Watery, large volume. Persists with fasting. Osmotic gap normal. Cholera, ETEC, S. aureus toxin.

Osmotic

Malabsorption

Stops with fasting. High osmotic gap. Giardia, lactose intolerance, laxative use, rotavirus.

Inflammatory

Invasive / Dysentery

Bloody mucoid stool. Fever. Small volume + tenesmus. Shigella, Campylobacter, STEC, Salmonella.

Aetiology — by Category

Category	Pathogens	Typical clinical clue	Common source
Bacterial Most common cause of acute ADD worldwide	Non-invasive / toxigenic: ETEC, V. cholerae, S. aureus, B. cereus, C. perfringens Invasive: Shigella, Salmonella, Campylobacter, STEC O157, EIEC, Yersinia enterocolitica, C. difficile	Fever + bloody diarrhoea = invasive. No fever + watery = toxigenic. STEC: bloody, no fever → HUS.	Contaminated food, water, person-to-person (Shigella), poultry (Campylobacter), beef (STEC)
Viral Most common in children <5	Rotavirus (children — leading cause globally), Norovirus (all ages — most common overall), Adenovirus (types 40/41), Astrovirus, Sapovirus	Vomiting prominent, watery diarrhoea, low fever. Winter season (Norovirus). Age <5 years (Rotavirus).	Person-to-person, contaminated water, shellfish (Norovirus), faecal-oral
Parasitic Subacute / travel-related	Giardia lamblia, Cryptosporidium parvum, Entamoeba histolytica (amoebic dysentery), Cyclospora cayetanensis, Isospora belli	Giardia: fatty floating stools. Entamoeba: bloody + mucus, travel history. Cryptosporidium: severe in HIV.	Contaminated water (Giardia, Cryptosporidium), travel to endemic areas (Entamoeba)
Non-infectious	Medications (antibiotics, laxatives, metformin, NSAIDs, proton pump inhibitors), IBD flare, ischaemic colitis, food allergy, toxins (mushroom, heavy metals), radiation colitis	No infectious contact; drug history; chronic IBD background; recent radiation therapy.	Drug history, underlying disease, toxic ingestion

Aetiology by Setting — Exam-Focused

Setting	Most likely pathogens	Key clue
Community / sporadic	Norovirus, Rotavirus (children), Campylobacter, Salmonella, ETEC	Most cases — no specific risk factor; faecal-oral spread
Foodborne outbreak ≥2 people, same food	<6h: S. aureus / B. cereus. 8–16h: C. perfringens. >12h: Salmonella, Campylobacter, Norovirus	Incubation period + food source narrows it immediately
Traveller's diarrhoea Travel to developing country	ETEC (#1 cause — 40–70%), Shigella, Salmonella, Campylobacter, Entamoeba, Giardia, Norovirus, Cyclospora	ETEC: watery, no blood. Shigella/Campylobacter: bloody + fever. Giardia: weeks later, fatty stools.
Healthcare-associated / antibiotic use	Clostridioides difficile — most important nosocomial cause	Recent antibiotics (especially clindamycin, cephalosporins, fluoroquinolones, amoxicillin). Hospital admission. Watery diarrhoea, fever, raised WBC.
Immunocompromised / HIV	Cryptosporidium, Microsporidium, Isospora, CMV colitis, MAC, Salmonella (recurrent)	CD4 count determines likely pathogen. Cryptosporidium + CD4 <200 = life-threatening chronic diarrhoea.
Day care / institutional	Rotavirus (children), Shigella, Giardia, Cryptosporidium, Norovirus	Children age <5. Close contact. Water play. Poor hand hygiene.
Seafood / shellfish	Norovirus, Vibrio parahaemolyticus, Vibrio vulnificus, Hepatitis A	Raw oysters → Norovirus. Vibrio: coastal areas, septicaemia in liver disease.

Risk Factors

Host risk factors

Age extremes — infants (immature immunity), elderly (↓ gastric acid, immunosenescence)

Immunocompromised — HIV, chemotherapy, steroids, transplant

↓ Gastric acid — PPI use, achlorhydria, gastrectomy → reduced barrier to infection

Antibiotic use — disrupts gut flora → C. difficile, overgrowth of pathogens

Malnutrition — impaired immunity, gut barrier dysfunction

Inflammatory bowel disease — susceptibility to superimposed infection

Pregnancy — Listeria, Salmonella carry higher risk of complications

Environmental / exposure risk factors

Contaminated water — untreated, well water, flooding (cholera, Giardia, Cryptosporidium)

Unsafe food handling — inadequate cooking, cross-contamination, improper storage

Travel to endemic areas — ETEC, Shigella, Entamoeba, Typhoid

Animal contact — reptiles (Salmonella), farm animals, petting zoos (STEC, Campylobacter)

Hospitalisation — C. difficile, nosocomial spread, antibiotic exposure

Crowded settings — refugee camps, prisons, cruise ships, military (Norovirus, Shigella)

Swimming pools / recreational water — Cryptosporidium (chlorine-resistant)

Factors increasing severity

Age <5 or >65 — rapid dehydration, mortality risk

Underlying renal disease — worsened by dehydration + STEC

Sickle cell disease — Salmonella bacteraemia + osteomyelitis

Delayed presentation — severe dehydration, electrolyte crisis

Inappropriate antibiotics — STEC → HUS; Salmonella → prolonged carriage

Loperamide misuse — toxic megacolon in Shigella/C. difficile

Lack of access to ORS — avoidable deaths, especially in children

Global burden: Acute diarrhoeal disease causes ~1.7 billion episodes/year globally. Second leading cause of death in children <5 years (after pneumonia). 90% of deaths occur in developing countries — largely preventable with safe water, ORS, and vaccines (Rotavirus, cholera, Typhoid). Malnutrition + diarrhoea = vicious cycle — each worsens the other.

Pathophysiology

Pathogen or toxin ingestion → intestinal infection or epithelial injury → altered secretion and absorption of water and electrolytes → increased stool water content → diarrhea → fluid and electrolyte loss → dehydration ± systemic complications

Clinical Presentation

-Symptoms:

Acute Diarrheal Disease commonly causes:

Frequent loose or watery stools
Abdominal cramps
Nausea
Vomiting
Fever
Malaise

Other features may include:

Urgency
Tenesmus
Blood or mucus in stool
Headache

-Signs:

Dry mucous membranes
Increased thirst
Tachycardia
Reduced urine output
Orthostatic hypotension
Abdominal tenderness
Fever

-Severe Disease

Severe Acute Diarrheal Disease may cause:

Severe dehydration
Hypovolemic shock
Electrolyte abnormalities
Acute Kidney Injury (AKI)
Sepsis
Altered mental status

Important Note Bloody diarrhea, high fever, severe abdominal pain, persistent vomiting, or marked dehydration should raise concern for invasive or complicated intestinal disease.

History Taking

-Ask about:

Onset and duration of diarrhea
Stool frequency and volume
Watery versus bloody stool
Fever and chills
Abdominal pain
Vomiting
Fluid intake and urine output
Recent food or water exposure
Recent travel
Sick contacts
Recent antibiotic use

Physical Examination

-General Examination

Temperature
Heart rate and blood pressure
Hydration status
Mental status
Signs of shock

-System-Specific Examination:

Abdominal tenderness
Abdominal distension
Bowel sounds
Guarding or peritonism when severe abdominal pathology is suspected

Investigations

-Biochemistry / Specific Tests

Serum electrolytes and renal function in significant dehydration
Stool culture or molecular testing in selected patients
Blood cultures when bacteremia or sepsis is suspected
Stool testing for specific pathogens when clinically indicated

-Imaging

Not routinely required.

Imaging may be appropriate when there is severe abdominal pain, suspected complications, or concern for an alternative diagnosis.

-Special / Confirmatory Tests

Stool testing should be considered with:

Bloody diarrhea
High fever
Severe illness
Persistent diarrhea
Suspected outbreak
Significant immunosuppression

Diagnosis

-Acute Diarrheal Disease is usually diagnosed clinically:

Acute onset of loose stools → assess hydration, stool characteristics, exposure history, and red flags → perform stool testing when indicated.

Home Home Clinical Cases Infectious System Clinical Cases Acute Diarrheal Disease

Management

Acute Diarrhoeal Disease · Assessment & Rehydration

No Dehydration

Fluid loss <5%

Alert, drinking normally
Normal skin turgor, eyes, mucosa
Normal urine output
No sunken fontanelle
Plan A — ORS at home

Some Dehydration

Fluid loss 5–10%

Restless, irritable, thirsty
Sunken eyes, dry mouth
Skin pinch returns slowly (>2 sec)
Decreased urine output
Plan B — ORS in clinic 4h

Severe Dehydration

Fluid loss >10%

Lethargic, unconscious
Very sunken eyes, no tears
Skin pinch returns very slowly (>3 sec)
Unable to drink / drinks poorly
Plan C — IV fluids urgently

Initial Assessment

History — key questions

Duration, frequency, volume of stools

Blood or mucus in stool — suggests invasive pathogen

Fever — temperature, duration

Vomiting — ability to take oral fluids

Recent food / water exposure, travel, antibiotic use

Contact with ill persons, animal exposure

Urine output — last void, colour

Examination

Vital signs — HR, BP, temp, RR

Capillary refill — >2 sec = poor perfusion

Skin turgor — pinch abdomen / back of hand

Mucous membranes + eyes — dryness

Fontanelle — sunken in infants

Abdomen — tenderness, distension, bowel sounds

Weight — compare to recent if possible

Red flags — admit immediately

Severe dehydration — lethargy, unable to drink

Bloody diarrhoea + high fever + systemic toxicity

Age <6 months or elderly with significant dehydration

Persistent vomiting — unable to maintain ORS

Signs of HUS — oliguria + pallor + petechiae after bloody diarrhoea

Immunocompromised, pregnancy, sickle cell

Abdominal rigidity / peritonitis signs

Rehydration — WHO Plans A / B / C

WHO Plan	Dehydration	Fluid	Dose & Method	Key points
Plan A	None	ORS — WHO low-osmolarity formula (75 mEq Na, 75 mmol glucose, 20 mEq K)	<2 yrs: 50–100 mL after each stool. 2–10 yrs: 100–200 mL after each stool. >10 yrs: as much as wanted. Continue feeding.	Home treatment. Return if worsening, blood in stool, not drinking.
Plan B	Some (5–10%)	ORS — supervised in clinic/hospital	75 mL/kg over 4 hours. Reassess every hour. If vomiting — small frequent sips (5 mL every 2–3 min). Continue breastfeeding throughout.	Reassess after 4h. If improved → Plan A. If worse → Plan C. Avoid juice/carbonated drinks.
Plan C	Severe (>10%)	IV Ringer's lactate — preferred. Normal saline if RL unavailable.	Infants <12 months: 30 mL/kg over 1h, then 70 mL/kg over 5h. Children >1yr / adults: 30 mL/kg over 30 min, then 70 mL/kg over 2.5h. Reassess every 15–30 min.	ICU/HDU. Monitor urine output. Electrolytes. Switch to ORS as soon as able to drink.

ORS composition (WHO low-osmolarity): Glucose 75 mmol/L + Na⁺ 75 mEq/L + K⁺ 20 mEq/L + Cl⁻ 65 mEq/L + Citrate 10 mmol/L = osmolarity 245 mOsm/L. Lower osmolarity reduces vomiting + stool output vs original formula. Rice-based ORS equally effective. Zinc supplementation 10–20 mg/day × 10–14 days — reduces duration + severity in children <5 (WHO recommendation).

Acute Diarrhoeal Disease · Antibiotic & Specific Treatment

Antibiotic Treatment — When & What

Pathogen / Condition	Antibiotic	When to treat	Avoid / Notes
Empirical — traveller's diarrhoea Watery, no blood, no fever	Azithromycin 1g single dose PO — preferred globally (low resistance) Ciprofloxacin 500 mg BD × 1–3 days — if azithromycin unavailable Rifaximin 200 mg TDS × 3 days — non-invasive, non-febrile only	Moderate–severe traveller's diarrhoea. Mild → supportive only.	Rifaximin: not for bloody/febrile diarrhoea
Shigella (dysentery)	Azithromycin 500 mg OD × 3 days — 1st line Ciprofloxacin 500 mg BD × 3 days — if sensitive Ceftriaxone 2g IV OD — severe / MDR	Always treat — reduces severity, duration, transmission	No loperamide — toxic megacolon risk
Campylobacter	Azithromycin 500 mg OD × 3 days — preferred (↑ fluoroquinolone resistance) Ciprofloxacin — only if sensitivity confirmed	Severe / prolonged (>7 days), immunocompromised, bacteraemia. Early treatment if within 3 days.	No benefit if started late (>3 days)
Salmonella NTS	Ciprofloxacin 500 mg BD PO or 400 mg IV BD Ceftriaxone 2g IV OD — fluoroquinolone resistant	Only if high-risk: age <1 or >65, immunocompromised, SCD, asplenia, bacteraemia	Routine cases: no antibiotics — prolong carriage No loperamide
E. coli O157 (STEC)	CONTRAINDICATED — all antibiotics increase Shiga toxin → HUS risk Supportive only: IV fluids, avoid NSAIDs, monitor renal function	Never — antibiotics worsen outcome	No antibiotics No loperamide No NSAIDs
C. difficile	Mild–moderate: Metronidazole 400 mg TDS PO × 10 days (resource-limited) Moderate–severe: Vancomycin 125 mg QDS PO × 10 days — preferred Recurrent: Fidaxomicin 200 mg BD × 10 days — lower recurrence rate	Always treat. Stop precipitating antibiotic if possible. Isolate patient.	No loperamide — toxic megacolon. Oral vancomycin not absorbed — acts locally in colon.
Cholera	Doxycycline 300 mg single dose — adults 1st line Azithromycin 1g single dose — children + pregnancy Ciprofloxacin 1g single dose — alternative	Moderate–severe cholera. ORS is cornerstone — antibiotics adjunct only.	ORS priority — antibiotics reduce duration 50% but hydration saves lives
Giardia	Metronidazole 400 mg TDS × 5–7 days Tinidazole 2g single dose — preferred (better compliance)	Always treat symptomatic infection	Avoid alcohol with metronidazole
Entamoeba histolytica Amoebic dysentery	Metronidazole 800 mg TDS × 5 days (tissue amoebiasis) Followed by: Diloxanide furoate 500 mg TDS × 10 days — luminal agent to clear cysts	Always treat. Need both agents — metronidazole alone misses luminal cysts → relapse.	Must complete luminal agent or relapse common
Cryptosporidium	Immunocompetent: supportive — self-limiting HIV/immunocompromised: Nitazoxanide 500 mg BD × 3 days + ART — CD4 recovery is key	Always treat in immunocompromised. No treatment in healthy patients.	ART (HIV) = most effective treatment — CD4 recovery clears infection

Antibiotic rules to memorise: Most acute diarrhoea = supportive only. Shigella — always treat. STEC — never treat with antibiotics. C. difficile — oral vancomycin preferred (metronidazole only if resource-limited). Amoeba — metronidazole + luminal agent (diloxanide). Campylobacter — azithromycin (fluoroquinolone resistance rising globally).

Adjunct & Supportive Measures

Medications

Ondansetron 4–8 mg PO/IV — antiemetic; allows ORS to be taken

Zinc 10–20 mg/day × 10–14 days — children <5 (WHO); reduces duration + future episodes

Loperamide — watery non-bloody, non-febrile only. Adult traveller's diarrhoea. Never in children <2, never in bloody/febrile diarrhoea.

Paracetamol — fever + cramping. Avoid NSAIDs (worsen GI mucosa + STEC outcome).

Probiotics — limited evidence; may shorten viral diarrhoea duration by 1 day

Nutrition

Continue feeding — early re-feeding shortens illness; prevents malnutrition

Continue breastfeeding — breast milk protective; do not stop during diarrhoea

Age-appropriate foods — rice, bread, banana, cooked vegetables. Avoid high-fat, high-sugar.

Avoid fasting — BRAT diet (Banana, Rice, Applesauce, Toast) — acceptable but not superior to normal diet

Avoid fruit juices + carbonated drinks — high osmolarity worsens osmotic diarrhoea

Infection control

Hand hygiene — soap + water (alcohol gel ineffective against Norovirus, C. difficile spores)

Isolate hospitalised patients — single room. Contact precautions.

Notify public health — Shigella, Cholera, Typhoid, STEC O157, C. difficile outbreaks

Exclude from food handling/childcare — Norovirus, Shigella, Salmonella until symptom-free 48h

Stool cultures — bloody diarrhoea, systemically unwell, travel, immunocompromised, outbreaks

Complications

Severe dehydration
Electrolyte disturbances
Hypovolemic shock
Acute Kidney Injury (AKI)
Sepsis
Hemolytic Uremic Syndrome (HUS)
Reactive arthritis
Malnutrition
Death in severe untreated disease

Prognosis

The prognosis of Acute Diarrheal Disease is generally excellent, with most uncomplicated infections resolving within several days. Prognosis is less favorable in infants, older adults, immunocompromised patients, and those with severe dehydration or invasive infection.

Key Points / Clinical Pearls

Acute diarrhea usually lasts less than 14 days.
Most cases are infectious.
Viruses are common causes of acute gastroenteritis.
Bloody diarrhea suggests inflammatory or invasive disease.
Dehydration is the most important immediate complication.
Oral rehydration is the main treatment for most patients.
IV fluids are required for severe dehydration or shock.
Stool testing is reserved for selected severe, persistent, bloody, or outbreak-associated cases.
Antibiotics are not routinely required for uncomplicated infectious diarrhea.
Antimotility drugs should be avoided with bloody diarrhea or high fever.
Severe disease can cause Acute Kidney Injury (AKI).

World Health Organization (WHO). Diarrhoeal Disease .
Shane AL, Mody RK, Crump JA, et al. 2017 Infectious Diseases Society of America Clinical Practice Guidelines for the Diagnosis and Management of Infectious Diarrhea. Clin Infect Dis. 2017;65(12):e45-e80. PubMed .
Riddle MS, DuPont HL, Connor BA. ACG Clinical Guideline: Diagnosis, Treatment, and Prevention of Acute Diarrheal Infections in Adults. Am J Gastroenterol. 2016;111(5):602-622. PubMed .
DuPont HL. Acute Infectious Diarrhea in Immunocompetent Adults. N Engl J Med. 2014;370(16):1532-1540. New England Journal of Medicine .
Guarino A, Ashkenazi S, Gendrel D, et al. European Society for Pediatric Gastroenterology, Hepatology, and Nutrition/European Society for Pediatric Infectious Diseases Evidence-Based Guidelines for the Management of Acute Gastroenteritis in Children in Europe. J Pediatr Gastroenterol Nutr. 2014;59(1):132-152. PubMed .
King CK, Glass R, Bresee JS, Duggan C. Managing Acute Gastroenteritis Among Children: Oral Rehydration, Maintenance, and Nutritional Therapy. MMWR Recomm Rep. 2003;52(RR-16):1-16. CDC .
National Library of Medicine (NIH). Acute Diarrhea . StatPearls.