The Curbsiders podcast

#266 Diarrhea Disemboweled Part 1: Acute Diarrhea with Dr. Iris Wang

April 5, 2021 | By

Flow with us through Diarrhea Disemboweled Part 1 as Dr. Xiao Jing (Iris) Wang @IrisWangMD  walks us through the evaluation and management of acute diarrhea.

NOTE: CME will not Go LIVE until Wed 4/7/21 for both #266 and #267. Then, claim 2 hours credit in one shot!

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  • Producer: Elena Gibson MD
  • Writer: Elena Gibson MD
  • Cover Art: Kate Grant, MD 
  • Hosts: Elena Gibson MD, Stuart Brigham MD; Matthew Watto MD, FACP; Paul Williams MD, FACP  
  • Editor: Matt Watto MD (written); Clair Morgan of (audio)
  • Guest: Xiao Jing (Iris) Wang MD

Sponsor: The American College of Physicians

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Show Segments

  • Intro, disclaimer, guest bio 
  • Picks of the Week 
  • Case from Kashlak 
  • Definitions
  • Small bowel vs. Large bowel pathology
  • Red flags
  • Microbiologic evaluation of acute diarrhea
  • Non-Culture based testing panels
  • Supportive Management
  • Post infectious diarrhea
  • Oral Rehydration Solution 
  • Take-Home points and Outro

Acute Diarrhea Pearls

  1. Diarrhea is “loosely” defined as >3 liquid or loose bowel movements in 24 hours (or more frequently than normal for an individual).
  2. Diarrhea can be categorized by time as 1) acute <2 weeks 2) persistent 2-4 weeks and 3) chronic >4 weeks.
  3. Large volume diarrhea is likely a result of pathology located in the small bowel to right colon.
  4. Diarrhea described as small volume with frequent episodes is likely a result of pathology in the left colon or rectum. 
  5. Red flags for severe acute diarrhea include fever, duration >72hr if immunocompetent (or <72h if immunocompromised), bloody stools, and hypovolemia. 
  6. Broaden the differential for infectious etiologies of acute diarrhea in patients who are immunocompromised to include: cytomegalovirus, Cryptosporidium, Cystoisospora, Mycobacterium avium complex, microsporidia, and disseminated TB. 
  7. The diagnosis of CMV induced colitis requires endoscopic evaluation and biopsies with  pathology-based testing of CMV 
  8. Consider endoscopic evaluation of acute diarrhea in cases of immunosuppression, mycophenolate use, checkpoint inhibitor therapy, or if concern for CMV colitis.
  9. Treatments for the supportive management of acute diarrhea include oral rehydration solution, loperamide, and bismuth.

Acute Diarrhea Notes 


Diarrhea is defined as (Riddle 2016)

  1. >3 liquid or loose bowel movements in 24 hours (or more frequently than normal for an individual)
  2. The more objective definition is stool weight >200g of stool per day 

Categorize by Timing (Riddle 2016)

  • Acute: <2 weeks
  • Persistent: 2-4 weeks
  • Chronic: >4 weeks

Diarrhea: The Initial Evaluation 

The History: 

It is important to clarify what a patient means by “diarrhea”. Is it loose stools, frequent stools or stool leakage (incontinence issue)? Different people have different baselines for what is normal. Ask about: 1) recent food exposures  2) sick contacts 3) travel or travel of close contacts 4) timeline of symptoms 5) stool characteristics.  Understanding if the diarrhea is small volume with increased frequency or less frequent, voluminous diarrhea helps localize the most likely source of pathology. The small bowel is primarily responsible for fluid reabsorption (PO intake and GI tract production) and the large intestine reabsorbs what remains. So, with large volume diarrhea the etiology is likely located from the small bowel to the right colon. The left colon, especially the rectum, serves as a stool reservoir, so pathology there will lead to reduced ability to hold on to stool and increased irritation. Rectal irritation is what causes the sense of needing to pass frequent bowel movements (tenesmus). As a result, frequent bowel movements with small amounts of stool indicate pathology located in the left colon or rectum. 

A bit on pathophysiology:

Diarrhea often results from a change in absorption rate that is the result of a change in 1) surface area or 2) contact time. For example, the presence of a large number of unabsorbed osmoles or fat will inhibit water binding for reabsorption and lead to diarrhea. 

Red flags: 

Fever, Duration (>72 hours in the immunocompetent patient and <72 in immunocompromised patients), bloody stools, signs of hypovolemia (AKI, weakness, dizziness, decreased UOP). Dysentery=grossly blood stools (Riddle 2016). This is important because it is important to differentiate grossly bloody stools from less concerning sources of blood (ie irritation of skin or hemorrhoid from excessive wiping). 

Diarrhea: The Lab Evaluation

General Labs

Check a BMP and CBC to evaluate hydration status, WBC, and Hgb/Hct to evaluate cell counts for infection and anemia. 

A microbiologic assessment is recommended in the following cases (Shane 2017):

  1. Dysentery
  2. Moderate or severe watery diarrhea
  3. Increased risk of spreading (ie healthcare worker, food industry worker, daycare worker)
  4. Prolonged illness (watery and duration >72h)
  5. Immunosuppression

*See ACG guideline flowchart to evaluate this (Riddle 2016; Fig 1)

If hospitalization is required, consider early microbiologic assessment for severity. Kashlak Pearl: Dr. Wang recommends considering etiologies of diarrhea that improve with fasting or dietary changes such as osmotic diarrhea if it resolves rapidly following hospital admission. 

Microbiological Testing

  • Bacterial: There are now various non-culture based panels that test for numerous pathogens (20+) using PCR or antigen testing. These tests are much faster than cultures, but the cost and the risk of “non-pathogenic” positives should be considered (Shane 2017, Hanson 2016). For example, Dr. Wang describes frequently finding positive EPEC results, but these can represent colonization. Regarding cultures, many labs group Salmonella, E Coli, Shigella, Yersenia, and Campylobacter together. If a patient has dysentery, send the PCR panel and cultures for specific organisms known to cause dysentery (EHEC, shigella, entamoeba) —Shane 2017
  • Viral: Testing should be considered in public health reportable cases (ie outbreak in daycare center, cruise ship) and specific cultures and PCR testing needs to be sent (Shane 2017). Don’t forget that COVID19 is one of the acute viral diarrhea pathogens!


In patients who are immunocompromised the infectious workup for acute diarrhea should be broadened (Shane 2017). PCR based panels for infectious etiologies are particularly helpful in these cases and testing for additional infectious causes including cytomegalovirus, Cryptosporidium, Cystoisospora, Mycobacterium avium complex, microsporidia and  disseminated TB should be considered. Endoscopy is more often indicated in the case of acute diarrhea in the setting of immunosuppression, specifically in the setting of treatment with mycophenolate, certain checkpoint inhibitors (ie pembrolizumab), or concern for CMV (Shane 2017, Bellaguarda 2020). Serologic CMV testing does not equal CMV induced gastrointestinal disease. To diagnose CMV colitis, a biopsy confirming the presence of CMV (by inclusions or immunohistochemistry testing) in the colon is necessary as serologic CMV testing is not diagnostic (Beswick 2016).

Diarrhea Management 

Supportive Treatments

For patients with mild illness supportive management = rehydration and loperamide or bismuth (Riddle 2016). 

  1. Loperamide: safe (once C.diff has been ruled out) and effective. Has been associated with toxic megacolon and  ileus development in C.diff. See prior Cdiff episode
  2. Oral rehydration solution is simple and works in both acute and chronic diarrhea. Sports Drinks (ie Gatorade, Powerade, etc) are not good for rehydration from diarrhea because of 1) the sodium potassium balance; they do not include enough sodium 2) they are hyperosmolar and can worsen diarrhea. Dr. Wang recommends that patients buy something like Pedialyte or make a balanced oral rehydration solution at home. There are recipes online. The ingredients are water with salt and sugar (see instructions from WHO here). 
  3. Bismuth is in the ACG guidelines for consideration for prevention of acute traveler’s diarrhea. Two useful effects of bismuth include 1) antiinflammatory effect of salicylate 2) antimicrobial effect of bismuth. Bismuth subsalicylate does not have the same potential for causing ulcers as other salicylates like aspirin. Caveats: Bismuth requires frequent dosing (3-4x per day), and side effects include: constipation, dark stools and blackening of the tongue. 

Empiric Antibiotics 

  • Traveler’s diarrhea: Empiric antibiotic therapy is recommended based on travel location (Riddle 2016). The 2017 IDSA guidelines recommend a fluoroquinolone (usually cipro) or azithromycin depending on local susceptibility patterns (Shane 2017).
  • EHEC should not be treated with antibiotics because of increased risk of hemolytic uremic syndrome (HUS) (Shane 2017). 
  • Consider avoiding antibiotic in non-typhoid salmonella because antibiotic treatment could prolong an asymptomatic carrier state and shedding (Healy 2019).

Post infectious Diarrhea

A decrease in surface area from loss of villi is often the etiology of diarrhea immediately following an infection (aka Post-infectious IBS). Dr. Wang notes that patients often develop lactose intolerance because lactase is at the very tip of microvilli and lactase is the disaccharidase most likely to get damaged following acute gastroenteritis.


  1. Strange Fruit by Billie Holiday 
  2. Prior Curbsiders Episodes
    1. #27 Conquer Irritable Bowel Syndrome
    2. #95 Food Intolerance & Celiac Disease
    3. #117 Clostridium Difficile
    4. #138 Inflammatory Bowel Disease
  3. Other Media 
    1. Core EM Diarrhea
    2. CPS Schema (see below)


Listeners will develop an approach to the basic evaluation and initial management of acute diarrhea

Learning objectives

After listening to this episode listeners will…  

  1. Define acute, persistent, and chronic diarrhea 
  2. Review the differential diagnosis for acute diarrhea
  3. Establish a framework for evaluating acute diarrhea in various clinical settings
  4. Review initial laboratory testing for acute diarrhea
  5. Identify when to complete a microbiologic evaluation for the etiology of acute diarrhea 
  6. Describe appropriate management of symptoms associated with acute diarrhea 


Dr. Wang reports no relevant financial disclosures. Drs. Watto, Williams and Gibson report no relevant financial disclosures. 


Gibson Elena, Wang Iris, Williams PN, Brigham SK, Watto MF. “#266 Diarrhea Disemboweled  Part 1: Acute Diarrhea with Dr. Iris Wang”. The Curbsiders Internal Medicine Podcast. Final publishing date April 5, 2021.

Recommended References

  1. ACG Acute Diarrhea Guidelines 2016
  2. IDSA 2017 Infectious Diarrhea Guidelines
  3. Schiller 2014 Chronic Diarrhea APDW/WCOG  
  4. 2014 AFP Acute diarrhea in Adults
  5. Evaluating the patient with Diarrhea Sweetser 2012
  6. Role of Bile Acids in Chronic diarrhea
  7. Exocrine Pancreatic insufficiency in Diabetic Patients


  1. April 6, 2021, 12:49pm Jessie O writes:

    I went to a pharmacology review conference a few years back, and the lecturer said (regarding poop) “if you can throw it, then it’s not c.diff”. That saying just seems like something you all would say. Also, I think Dr. Iris is my spirit animal and we need to be bff’s.

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The Curbsiders are partnering with VCU Health Continuing Education to offer FREE continuing education credits for physicians and other healthcare professionals. Visit and search for this episode to claim credit.

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