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Diarrhea: Acute, Sub acute, & Chronic

Study guide:


  • It is the passage of loose\watery stool at least 3 times per 24 hours (>200 ml).

  • Classification based on duration:     

    • Acute: <2 weeks

    • Sub-acute: 2-4 weeks

    • Chronic: >4 weeks

  • Classification based on etiology: mainly for acute

    • Community acquired

    • Nosocomial/ Hospital-acquired 


  1. Community acquired: 

    • Viral:

      • Rotavirus

      • Norovirus 

    • Bacterial:


        1. Mechanism:

          • Fluid loss from the proximal small intestine without cellular injury.

        2. Course:

          • Acute, brief 1-3 days

          • Self limited. 

        3. Common microorganisms:


    1. Primary site for colonization: colon. 

    2. Characteristics:

      • Diarrhea in smaller volume than in watery diarrhea BUT lasts longer.

      • Diarrhea with BLOOD + PUS.

      • Inflammation and/or distinctive changes in the colonic mucosa.

    3. Presents as: fever, abdominal pain and cramps, & tenesmus.

      • Most cases resolve spontaneously in 2-7 days.

    4. Common pathogens:

Note: CHESS commonly cause bloody stool: Campylobacter, Hemorrhagic E.coli, E.histolytica,  Salmonella, Shigella.


    1. Salmonella enterica serovar typhi.

    2. Presents as: gradual onset of a systemic infection with fever and abdominal pain"(diarrhea is not a constant feature!)


  • Nosocomial/ Hospital-acquired: 

    • Infants:

      • Rotavirus -> winter time, breakouts.

      • Enteropathogenic E.coli (EPEC): infantile diarrhea.

    • Adults:  

      • Antibiotic associated diarrhea:

        1. S\E of antibiotics (erythromycin, augmentin, cephalexin, Clindamycin)

        2. C.difficile overgrowth (takes 3 days).

      • Non- antibiotic associated diarrhea: 

        1. CT contrast.

        2. Laxatives, magnesium, and sorbitol.

        3. Tube feed diarrhea


  • Travelers’ diarrhea: ingestion of fecally contaminated food, water, or ice. 

  • Causes:

    1. ​80% is bacterial cause.

    2. 50% of all cases: Enterotoxigenic E.coli.

    3. 10%-20% of cases: Shigella.

    4. Other: campylobacter jejuni.

  • Diagnosis of Acute & Subacute Diarrhea: 

    • Exclude infection (stool study) GOLD STANDARD for acute diarrhea. 

    • Checking for: mucus, blood (RBCs), WBCs.

    • If negative go for Endoscopy. 


  • Management of Acute & Subacute Diarrhea:


  • Classified according to the characteristic of stool:


    1. Mechanism:

      • Derangement of electrolyte and fluid transport across the intestinal epithelium.

      • (Special channels in the walls are disturbed).

    2. Etiology:

      • Medication: ethanol, stimulant laxatives.

      • Anatomical defects (bowel resection) and Congenital (chloridorrhea, mucosal defect…).

      • Toxins (e.g. vibrio cholera).

      • Hormones & neuroendocrine tumors (e.g. VIPoma, gastrinoma…).

    3. NOT affected by FASTING!


    1. Mechanism:

      • Osmotically active solute: driving water into the lumen.

    2. Etiology: 

      1. Osmotic laxatives (poorly absorbed ions: Mg++, SO4+).

      2. Non-absorbable sugars (artificial sweeteners, lactose intolerance).

    3. Gets better with FASTING!

  • FATTY 

    • Characteristics: malodourous, bulky stool, difficult to flush

      • Floating is due to gas not fat. 

    • Mechanism:

      • Mal-absorption:

        • Mucosal diseases (celiac disease)

        • Short bowel syndrome (after surgery)

      • Mal- digestion:

        • Pancreatic insufficiency (chronic pancreatitis)

        • Cholecystectomy:

          • Mechanism: bile will drain directly into small intestine -> exceed the terminal ilium absorptive capacity -> too much bile reaching the colon -> diarrhea 

      • Post-mucosal lymphatic obstruction. 



    • Presents as: pain, fever, cramps, and bloody diarrhea.

    • Etiology: 

      1. Inflammatory bowel disease (IBD) -> crohn’s disease, and ulcerative colitis.

      2. Infections (C. diff colitis, Yersinia, TB)

      3. Always exclude infection in inflammatory (bloody) diarrhea, even if you are sure of your diagnosis.

Osmotic Gap 50-100 mosm \ Kg

> 100 Osmotic Diarrhea 

normal pH: 7-7.5

pH high

pH low




Secretory Diarrhea


    • Etiology:

      1. Diabetic neuropathy à disturbance in symp. / parasymp.

      2. Hyperthyroidism à bowels hyper-motile

      3. Addison’s disease

      4. Irritable Bowel Syndrome (IBS):

                         A. Mechanism: stress -> hyperactive colon.  
                         B. More in females.
                         C. Presentation: chronic lower abdominal PAIN+ changes in the bowel habits (diarrhea, constipation, or both).
                         D. Dx.: Manning and Rome criteria.

  • Diagnosis of Chronic Diarrhea:

    • CBC: looking for leukocytosis.

    • Chemistry: looking for electrolyte disturbances.

    • Stool: occult blood.

    • Fecal leukocyte: suggestive of infections.

    • Biopsy for inflammatory bowel disease.

  • Management of Chronic Diarrhea:

    • Treat the underlying cause

    • Symptomatic 


  • Kumar P, Clark M. Kumar & Clark's clinical medicine.

  • Le T, Krause K. First aid for the basic sciences. New York: McGraw-Hill Medical; 2012.

  • Le T, Bhushan V, Singh Bagga H. First aid for the USMLE step 2 CK. New York: McGraw-Hill Medical; 2010.

  • Bergin J. Medicine recall. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins; 2008.

  • Collins P, Fox C. Gastroenterology. Edinburgh: Mosby; 2008.

  • Fischer C. Master the boards.

  • Agabegi S, Agabegi E, Ring A. Step-up to medicine. Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins; 2013. 

Written by:                 Haifa Al-Issa     
Reviewed by:             Roaa Amer
                                       Haneen Al-Farhan
​Format Editor:           Roaa Amer

Website publisher:  Salman Alahmed

                                       Bayan Alzomaili

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