Overview
Acute Diarrhea
1. Clinical Overview
Summary
Acute diarrhea (≥3 loose stools/day, <14 days) is usually viral and self-limited. Priority: assess and correct dehydration. Antibiotics NOT needed for most. Test for C. diff if recent antibiotics. Bloody diarrhea = stool cultures. Avoid loperamide if bloody or CDI.
Key Facts
- Definition: ≥3 loose stools/day, <14 days
- Cause: Viral (norovirus most common in adults)
- Treatment: Oral rehydration solution (ORS); IV if severe
- C. diff: Test if recent antibiotics; treat with vancomycin PO
2. Epidemiology
Overview
Acute diarrhea is defined as ≥3 loose or watery stools per day lasting <14 days. Most cases are infectious and self-limited. The key ED tasks are assessing hydration, identifying patients needing workup or antibiotics, and providing appropriate supportive care.
Classification
By Duration:
| Type | Duration |
|---|---|
| Acute | <14 days |
| Persistent | 14-30 days |
| Chronic | >0 days |
By Mechanism:
| Type | Features |
|---|---|
| Watery/Secretory | High-volume, no blood |
| Inflammatory/Invasive | Blood, mucus, fever |
Epidemiology
- Very common: ~179 million episodes/year in US
- Leading cause of morbidity worldwide
- Most self-limited: Lasts 1-3 days
Etiology
Viral (Most Common):
| Virus | Notes |
|---|---|
| Norovirus | Most common in adults |
| Rotavirus | Common in children |
| Adenovirus |
Bacterial:
| Organism | Features |
|---|---|
| Campylobacter | Bloody diarrhea, poultry |
| Salmonella | Eggs, poultry |
| Shigella | Bloody diarrhea, high fever |
| E. coli (STEC/EHEC) | Bloody diarrhea, HUS risk |
| C. difficile | Antibiotic-associated |
| Vibrio | Shellfish, seafood |
Parasitic:
| Organism | Notes |
|---|---|
| Giardia | Camping, contaminated water |
| Cryptosporidium | Immunocompromised, contaminated water |
| Entamoeba histolytica | Travel, dysentery |
3. Pathophysiology
Mechanism
Secretory:
- Toxin-mediated (e.g., cholera toxin, ETEC)
- Increased secretion without mucosal damage
- Watery, high-volume
Inflammatory/Invasive:
- Mucosal invasion (Shigella, Salmonella, Campylobacter)
- Blood, mucus, fever
- Lower volume but more severe symptoms
4. Clinical Presentation
Symptoms
| Symptom | Description |
|---|---|
| Diarrhea | ≥3 loose stools/day |
| Nausea/Vomiting | Common with viral |
| Abdominal cramps | Periumbilical or diffuse |
| Fever | More common with invasive |
| Blood in stool | Invasive pathogens |
| Dehydration | Thirst, dry mouth, decreased urine |
History
Key Questions:
Physical Examination
Assess Hydration:
| Finding | Mild | Moderate | Severe |
|---|---|---|---|
| Mental status | Normal | Restless | Lethargic |
| Thirst | ± | Increased | Unable to drink |
| Heart rate | Normal | Elevated | Very elevated |
| Blood pressure | Normal | Normal or low | Hypotensive |
| Mucous membranes | Moist | Dry | Very dry |
| Skin turgor | Normal | Decreased | Tenting |
| Urine output | Normal | Decreased | Minimal |
Abdominal Exam:
| Finding | Significance |
|---|---|
| Diffuse tenderness | Common |
| Rebound/guarding | Concerning (colitis, perforation) |
| Hyperactive bowel sounds | Common |
Duration and frequency of stools
Common presentation.
Blood or mucus in stool
Common presentation.
Fever
Common presentation.
Vomiting
Common presentation.
Oral intake, urine output
Common presentation.
Recent travel
Common presentation.
Recent antibiotics or hospitalization
Common presentation.
Sick contacts, food exposures
Common presentation.
Immunocompromise
Common presentation.
5. Clinical Examination
(Integrated into Clinical Presentation above)
Red Flags
Serious Conditions to Consider
| Finding | Concern | Action |
|---|---|---|
| Bloody diarrhea | Invasive pathogen, HUS | Stool cultures, avoid antimotility |
| High fever (>8.5°C) | Invasive infection | Stool cultures |
| Severe abdominal pain | Colitis, perforation | Consider imaging |
| Signs of severe dehydration | Hypovolemic shock | IV fluids |
| Immunocompromised | Opportunistic infections | Broader workup |
| Recent antibiotics | C. difficile | Test for CDI |
| HUS symptoms (pallor, oliguria) | STEC-HUS | CBC, BMP, smear |
6. Investigations
Differential Diagnosis
| Diagnosis | Features |
|---|---|
| C. difficile colitis | Recent antibiotics, watery or bloody |
| Inflammatory bowel disease | Chronic, bloody, weight loss |
| Ischemic colitis | Elderly, bloody, vascular risk factors |
| Medication-induced | Laxatives, metformin, etc. |
| Malabsorption | Chronic, steatorrhea |
| Hyperthyroidism | Weight loss, palpitations |
Diagnostic Approach
When to Test
Stool Studies Indicated:
- Bloody diarrhea
- Severe illness or fever
- Duration >7 days
- Immunocompromised
- Recent antibiotics (C. diff)
- Recent hospitalization
- Suspected outbreak
Testing Options
| Test | Indication |
|---|---|
| Stool culture | Bacterial pathogens |
| Stool O&P | Parasites (travelers, persistent) |
| C. difficile toxin (PCR or EIA) | Recent antibiotics, hospitalization |
| Shiga toxin / STEC | Bloody diarrhea, HUS concern |
| Fecal leukocytes/Lactoferrin | Inflammatory diarrhea |
Laboratory
| Test | Indication |
|---|---|
| BMP | Assess dehydration, electrolytes |
| CBC | Severe illness, HUS |
| Blood cultures | If septic |
Imaging
- Not routinely indicated
- CT abdomen if: Severe pain, peritoneal signs, toxic megacolon suspected
7. Management
Principles
- Rehydration is priority: Oral or IV
- Most cases viral and self-limited: No antibiotics
- Antibiotics for specific indications: Severe, invasive, traveler's, CDI
- Avoid antimotility in bloody diarrhea or CDI
Rehydration
Mild-Moderate Dehydration:
| Intervention | Details |
|---|---|
| Oral rehydration solution (ORS) | WHO formula or commercial (Pedialyte, Drip Drop) |
| Clear fluids | Water, broth, diluted juice |
| Avoid | Sugary drinks, caffeine |
Severe Dehydration:
| Intervention | Details |
|---|---|
| IV fluids | NS or LR; bolus then replacement |
| Monitor | Urine output, vitals |
Antimotility Agents
Loperamide:
| Dose | Notes |
|---|---|
| 4 mg initially, then 2 mg after each loose stool (max 16 mg/day) | DO NOT USE if bloody diarrhea, fever, or suspected CDI |
Bismuth Subsalicylate:
| Dose | Notes |
|---|---|
| 524 mg q30-60 min PRN (max 8 doses/day) | Safe; may reduce frequency |
Antibiotic Therapy
When to Use Antibiotics:
| Indication | Notes |
|---|---|
| Traveler's diarrhea (moderate-severe) | Empiric fluoroquinolone or azithromycin |
| Shigella (documented) | Azithromycin or fluoroquinolone |
| C. difficile | Vancomycin PO or fidaxomicin |
| Cholera | Doxycycline or azithromycin |
| Giardia/Entamoeba | Metronidazole or tinidazole |
NOT Recommended:
- Salmonella (may prolong carriage unless severe or immunocompromised)
- STEC/EHEC (may increase HUS risk)
Traveler's Diarrhea:
| Agent | Dose | Duration |
|---|---|---|
| Azithromycin | 500 mg daily or 1g × 1 | 1-3 days |
| Ciprofloxacin | 500 mg BID | 1-3 days |
| Rifaximin | 200 mg TID | 3 days |
C. difficile Infection:
| Severity | Treatment |
|---|---|
| Mild-moderate | Vancomycin 125 mg QID PO × 10 days OR Fidaxomicin 200 mg BID × 10 days |
| Severe | Vancomycin 125 mg QID PO × 10-14 days |
| Fulminant | Vancomycin 500 mg QID PO + Metronidazole 500 mg IV q8h |
8. Complications
Disposition
Discharge Criteria
- Mild-moderate dehydration corrected
- Able to tolerate oral fluids
- No severe symptoms or red flags
- Follow-up arranged
Admission Criteria
- Severe dehydration requiring ongoing IV fluids
- Unable to tolerate oral intake
- Severe abdominal pain or peritoneal signs
- Toxic appearance or sepsis
- Bloody diarrhea with HUS concern
- Severe C. difficile (ileus, toxic megacolon)
- Immunocompromised with severe illness
Follow-Up
| Situation | Follow-Up |
|---|---|
| Uncomplicated | PCP if not improved in 2-3 days |
| Stool cultures sent | PCP for results |
| C. difficile | Infectious disease or GI |
11. Patient/Layperson Explanation
Condition Explanation
- "You have acute diarrhea, which is most often caused by a viral infection."
- "It usually gets better on its own in 1-3 days."
- "The most important thing is to stay hydrated."
Home Care
- Drink plenty of fluids (ORS, water, broth)
- Continue eating bland foods as tolerated (BRAT diet: bananas, rice, applesauce, toast)
- Avoid dairy, caffeine, alcohol, fatty or spicy foods
- Wash hands frequently to prevent spread
Warning Signs to Return
- Blood in stool
- High fever
- Severe abdominal pain
- Dizziness or fainting
- Inability to keep fluids down
- No urine for >8 hours
9. Prognosis & Outcomes
Special Populations
Immunocompromised
- Broader differential (CMV, MAC, Cryptosporidium)
- Lower threshold for testing and admission
- Consider ID consultation
Elderly
- Higher risk of dehydration
- May have atypical presentation
- Lower threshold for IV fluids
Travelers
- Consider empiric antibiotic (azithromycin)
- Test for parasites if persistent
Hospitalized Patients
- C. difficile is leading concern
- Test and contact precautions
Quality Metrics
Performance Indicators
| Metric | Target | Rationale |
|---|---|---|
| Hydration assessed and documented | 100% | Priority |
| Stool testing for bloody diarrhea | 100% | Identify invasive pathogens |
| Avoid antibiotics for uncomplicated viral | >0% | Stewardship |
| CDI tested in recent antibiotic use | >0% | Appropriate workup |
Documentation Requirements
- Duration and frequency of diarrhea
- Bloody or non-bloody
- Hydration status
- Red flag assessment
- Travel, antibiotics, exposures
- Treatment and follow-up plan
10. Evidence & Guidelines
Key Clinical Pearls
Diagnostic Pearls
- Most is viral: Self-limited in 1-3 days
- Bloody diarrhea = Stool cultures: Shigella, Campylobacter, STEC
- Recent antibiotics = CDI: Test for C. diff
- Traveler + diarrhea = Consider empiric treatment
- HUS: STEC + bloody diarrhea + renal failure: Avoid antibiotics
- Hydration status is key assessment
Treatment Pearls
- ORS is effective: For mild-moderate dehydration
- IV fluids for severe: NS or LR
- Loperamide is helpful: EXCEPT bloody diarrhea or CDI
- Most don't need antibiotics: Viral is most common
- Azithromycin for traveler's diarrhea: Or fluoroquinolone
- Vancomycin PO for CDI: Not metronidazole (anymore)
Disposition Pearls
- Most can be discharged: After rehydration
- Admit for severe dehydration, HUS concern, or toxic appearance
- Follow-up for stool culture results
- Educate on hand hygiene: Prevent spread
12. References
- Shane AL, et al. 2017 Infectious Diseases Society of America Clinical Practice Guidelines for the Diagnosis and Treatment of Infectious Diarrhea. Clin Infect Dis. 2017;65(12):e45-e80.
- McDonald LC, et al. Clinical Practice Guidelines for Clostridium difficile Infection in Adults. Clin Infect Dis. 2018;66(7):e1-e48.
- Riddle MS, et al. ACG Clinical Guideline: Diagnosis, Treatment, and Prevention of Acute Diarrheal Infections in Adults. Am J Gastroenterol. 2016;111(5):602-622.
- DuPont HL. Acute infectious diarrhea in immunocompetent adults. N Engl J Med. 2014;370(16):1532-1540.
- Thielman NM, Guerrant RL. Acute Infectious Diarrhea. N Engl J Med. 2004;350(1):38-47.
- Connor BA. Travelers' Diarrhea. CDC Yellow Book. 2024.
- Steffen R, et al. Traveler's diarrhea: a clinical review. JAMA. 2015;313(1):71-80.
- UpToDate. Approach to the adult with acute diarrhea in resource-abundant settings. 2024.