Acute diarrhea

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This page is for adult patients. For pediatric patients, see: diarrhea (peds)


Gasterointestinal anatomy.
Layers of the Alimentary Canal. The wall of the alimentary canal has four basic tissue layers: the mucosa, submucosa, muscularis, and serosa.
  • Almost all true diarrheal emergencies are of noninfectious origin
  • 85% of diarrhea is infectious in etiology
    • Viruses cause vast majority of infectious diarrhea
    • Bacterial causes are responsible for most cases of severe diarrhea


  • Diarrhea: Increased frequency of defection, usually >3 bowel movements per day
  • Hyperacute: 1-6 hr
  • Acute: less than 3 weeks in duration
  • Gastroenteritis: Diarrhea with nausea and/or vomiting
  • Dysentery: Diarrhea with blood/mucus/pus
  • Invasive = Infectious

Clinical Features

Bristol Stool Chart.


Physical Exam

Differential Diagnosis

Acute diarrhea



Watery Diarrhea

Traveler's Diarrhea


Causes of Diarrhea.png

Toxigenic v. Infectious

Characteristic Toxic Infectious/Invasive
Incubation 2-12h 1-3d
Onset abrupt gradual
Duration <10-24h 1-7days
Fever No Yes
Abdominal Pain Minimal Yes, tenesmus
Systemic No Yes, myalgias, nausea and vomiting
Physical findings Nontoxic Toxic
Abdominal Tenderness No Yes
Stool Blood, WBCs No Yes

Indications for Workup

Indicated for:

  • Profuse watery diarrhea with signs of hypovolemia
  • Severe abdominal pain
  • Fever >38.5 (101.3) (suggests infection with invasive bacteria)
  • Symptoms >2-3d
  • Blood or pus in stool (E. coli 0157:H7)
  • Recent hospitalization or antibiotic use
  • Elderly or immunocompromised
  • Systemic illness with diarrhea (esp if pregnant (listeria))

Stool Studies

Fecal leukocytes

  • Used to differentiate invasive from noninvasive infectious diarrheas
  • Sn 50-80%, Sp 83% for presence of bacterial pathogen
  • If patient has +leukocytes but negative infection consider IBD

Stool culture

  • Plays minor role in ED evaluation
  • Yield is only 1.5-5.5%
  • Consider in patients with
    • Immunosuppression
    • Severe, inflammatory diarrhea (including bloody diarrhea)
    • Underlying IBD (need to distinguish between flare and superimposed infection)


  • Indicated if parasitic cause is suspected:

C. diff toxin

  • 10% false negative rate
  • Turnaround time for results varies by institution


  • Warranted in severely dehydrated patients



Supportive Therapies

Oral rehydration therapy

  • Fluids should contain sugar, salt, and water


  • Lactobacilli and bifidobacterium
  • 25% decrease in average duration of diarrhea (good evidence)

Diet Modification

  • Eat: BRAT(Bananas, Rice, Applesauce and Toast) diet (no evidence)
  • Avoid: Caffeine (increased gastric motility), raw fruit (increased osmotic diarrhea), lactose

Bismuth subsalicylate

  • Consider when loperamide is contraindicated (high fever, dysentery)
  • Dose: 30 mL or 2tab q30 min for 8doses; repeat on day 2
  • Caution: may cause bismuth encephalopathy in HIV patients


  • 2mg PO per dose
    • Start: 4mg PO x1, then 2mg PO after each loose stool; Max: 16mg/day
  • Contraindicated if suspect C. diff


  • Dose: 4mg QID x2d
  • 2nd line agent (may cause cholinergic side effects)
  • Contraindicated in pseudomembranous colitis, obstructive jaundice, and children <6y

Antibiotics for Infectious Diarrhea

  • Most cases of diarrhea are NOT from infectious causes. If the patient suspects that there is blood in the stool but there is no abdominal pain, and no fever, the cause is unlikely to be from a bacterial cause. Also avoid antibiotics in E. Coli 0157:H7 (EHEC) cases due the risk of Hemolytic Uremic Syndrome (HUS)[2]
  • The majority of patients, even with bacterial positive cultures, will recover from diarrhea illness without antibiotic therapy[3]

Relative Indications for Antibiotics[4]

  • Suspected bacterial diarrhea
  • Bloody diarrhea (except for EHEC) with fever and systemic illness
  • Occult blood or +fecal leukocytes
  • Moderate to severe travelers' diarrhea (>4 stools/d, fever, blood, or mucus in stool)
  • >8 stools/d
  • Volume depletion
  • >1wk duration
  • Immunocompromised
  • Toxic appearance

Empiric Therapy

Traveler's Diarrhea

Adult Options:

Pediatric Options:

Avoid fluroquinolones

Culture Specific Antibiotics

Agent Treatment
Clostridium difficile
Campylobacter jejuni
Entamoeba histolytica
Giardia lamblia
Salmonella (non typhoid)
  • Treatment is not recommended routinely but should be considered if:
  • Immunocompromised
  • Age<6 mo or >50yo
  • Has any prostheses
  • Valvular heart disease
  • Severe Atherosclerosis
  • Active Malignancy
  • Uremic

Options: Immunocompromised patients should have 14 days of therapy

Shigella Treatment extended for 10 days if immunocompromised'
Vibrio Cholerae
Yersinia enterocolitica Antibiotics are not required unless patient is immunocompromised or systemically ill


  • Hospitalization should be individualized based on the patient's ability to tolerate oral hydration, have adequate social support, and also based on complicating comorbidities.
  • Majority of patients can be treated as an outpatient
  • Observation or admission is required for those with severe disease, and significant dehydration with other end organ complications

See Also


  1. Marx et al. “Cholera and Gastroenteritis caused by Noncholera Vibrio Species”. Rosen’s Emergency Medicine 8th edition vol 1 pg 1245-1246.
  2. Aranda-Michel J et al. Acute diarrhea: A practical review. AmJMed. 1999;106:670-676.
  3. DuPont HL et al. Practice Parameters Committee of the American College of Gastroenterology. Guidelines on acute infectious diarrhea in adults. Am J Gastroenterol. 1997;92:1962-1975.
  4. IDSA Practice Guidelines for the Management of Infectious Diarrhea. 2001. fulltext
  5. Hoge CW. et al. Trends in antibiotic resistance among diarrheal pathogens isolated in Thailand over 15 years. Clin Infect Dis. 1998;26:341–5
  6. Steffen R, et al. Traveler’s Diarrhea: A Clinical Review. JAMA. 2015;313(1):71-80. doi:10.1001/jama.2014.17006
  7. Sanders JW. et al. An observational clinic-based study of diarrheal illness in deployed United States military personnel in Thailand: presentation and outcome of Campylobacter infection. Am J Trop Med Hyg. 2002;67:533–8
  8. Steffen R, et al. Traveler’s Diarrhea: A Clinical Review. JAMA. 2015;313(1):71-80. doi:10.1001/jama.2014.17006
  9. Steffen R, et al. Traveler’s Diarrhea: A Clinical Review. JAMA. 2015;313(1):71-80. doi:10.1001/jama.2014.17006
  10. DuPont HL. et al. Rifaximin versus ciprofloxacin for the treatment of traveler’s diarrhea: a randomized, double-blind clinical trial. Clin Infect Dis. 2001;33:1807–15
  11. Stauffer WM, Konop RJ, Kamat D. Traveling with infants and young children. Part III: travelers’ diarrhea. J Travel Med. 2002;9:141–50