creation date: 2025-11-10 13:56
tags: Pathologies
Diarrhea
Background
Definitions
Diarrhea refers to an increase in water content in stool resulting in watery or loose stool, and is typically defined as at least three times in 24 hours.
Further definition has been used according to duration:
- Acute: ≤14 days
- Persistent:14-30 days
- Chronic: >30 days
It should be noted that acute gastroenteritis is often used synonymously but can be inaccurate as it suggests both gastric and small intestinal involvement which is rarely the case with diarrhea.
Etiology
Acute diarrhea is most commonly caused by infection.
Viral causes are common with majority of cases due to:
- Rotovirus (most common overall)
- Norovirus (most common in countries with rotovirus vaccination)
- Adenoviruses
Bacterial causes are typically the cause of more severe diarrhea. Major causes and their associated sources/risk factors include:
| Bacteria | Sources/risk factors |
|---|---|
| Aeromonas hydrophila | Eating seafood, meats, vegetables like sprouts; medicinal leech therapy |
| Bacillus cereus | Eating rice (reheated rice syndrome), dairy products, spices, bean sprouts, certain vegetables |
| Campylobacter spp. | Eating poultry, meat, unpasteurized milk; resource-limited settings; contact with puppies and kittens; Campylobacter jejuni can cause GBS |
| Clostridioides difficile | Antibiotics use, hospital stays, chemotherapy, gastric acid suppression, inflammatory bowel disease |
| Clostridium perfringens | Eating meat, poultry, home-canned goods |
| Enterotoxigenic E. coli | Fecal contamination of food/water; resource-limited settings; aka. Traveler’s diarrhea |
| Enterohemorrhagic E. coli | Eating ground beef, fresh produce, unpasteurized milk/juice; daycare centres and nursing homes; extremes of age |
| Klebsiella oxytoca | Exposure to contaminated water or soil; healthcare setting (contamination) |
| Listeria monocytogenes | Eating processed deli meats, hot dogs, soft cheese, pates, fruits; pregnancy, immunosuppression, extremes of ages |
| Plesiomonas shigelloides | Consumption of raw shellfish, contaminated vegetables or water; contact with freshwater aquariums or fish tanks; exposure to amphibians or reptiles |
| Salmonella spp. | Eating undercooked or raw animal products (poultry, eggs, meat, unpasteurized milk); contact with infected animals (reptiles, pets with diarrhea) |
| Shigella spp. | Eating raw vegetables; daycare centres, crowded living conditions, men having sex with other men; resource-limited settings |
| Staphylococcus aureus | Consumption of processed meats, dairy products, mayonnaise, cream-filled pastries; cross contamination |
| Vibrio parahemolyticus | Eating raw seafood and shellfish; cirrhosis |
| Yersinia spp. | Consuming pork or untreated water; blood transfusions; iron metabolism abnormalities (eg. hemochromatosis, cirrhosis, thalassemia) |
| Chlamydia trachomatis Neisseria gonorrhea Treponema pallidum | Men having sex with other men (sign of proctitis) |
Protozoal causes of diarrhea include Blastocystis spp., Dientamoeba fragilis, Giardia duodenalis, and Cryptosporidium spp. These are particularly significant in low-resource settings.
Noninfectious causes become more likely as duration of diarrhea increases. Causes include:
- Malabsorption (eg. steatorrhea)
- Inflammatory bowel disease
- Medication side effects
- Cancer
Pathogenesis
A number of mechanisms can result in diarrhea.
Osmotic
Poorly absorbed solutes in the lumen of the intestines can draw water osmotically. Examples of this include lactose intolerance, sorbitol ingestion, and Mg laxatives. Typical features includes:
- Cessation with fasting
- Stool osmotic gap >50 mOsm/kg
Secretory
Secretory diarrhea occurs due to active intestinal secretions of electrolytes. This mechanism is associated with large-volume watery stools which does not cease with fasting. Examples include cholera, enterotoxic E. coli, VIPoma, and bile acid malabsorption.
Exudative, inflammatory, infectious
Mucosal damage of the intestine results in leakage of mucus, proteins, and blood. This increases the concentration of osmotically active components within the intestinal lumen resulting in increased water content. Additionally, bacteria can stimulate fluid secretion through toxins, stimulation of inflammatory cascade, and disruption of physiological microbiota.
Motility-related
Rapid transit of content through the bowel reduces the capability to absorb water. Stasis may allow for bacterial overgrowth.
Clinical Presentation
Signs & Symptoms
In most cases, acute diarrhea is self-limiting with limited associated symptoms.
Some pathogens may have specific associated symptoms (eg. rotavirus with vomiting, dehydration).
Diarrhea of small bowel origin is typically watery, larger in volume, and associated with cramping, bloating, and gas. Fever is uncommon.
Diarrhea of large bowel origin is typically more frequent, regular, smaller in volume, and often painful. Fever and bloody stool are common.
History & Physical Exam
History should elicit:
- Duration of symptoms
- Frequency and characteristics of stool
- Associated symptoms
- Evidence of extracellular volume depletion
- Potential exposures (food, residence, occupational, travel, pets)
- Recent antibiotic use
- Medications (eg. PPI)
- Immunocompromised status
These clues can point towards a likely pathogen.
Physical exam should focus on evaluating volume status and possible complications. An abdominal exam should be completed.
Diagnosis
Criteria
Diarrhea is diagnosed by presence of watery stool three times within 24 hours.
Work-up
Routine laboratory testing is not necessary for acute diarrhea.
If significant volume depletion is present, a basic metabolic panel should be performed. A CBC may be helpful in evaluating for complications.
In patients with severe illness, blood diarrhea, signs of inflammatory diarrhea, high-risk features, persistent symptoms (>1 week), and/or public health concerns, a stool culture is indicated.
Differential
Red Flags / Complications
Generally, signs of severe infection, dehydration, or underlying systemic disease should warrant prompt evaluation.
Management
Prophylaxis
Prophylaxis is available for traveler’s diarrhea. Dukoral is an over-the-counter option that is generally effective against ETEC and cholera.
For first-time use: first dose at least 2 weeks prior to departure and second dose 1 week after first dose. Protection starts 1 week following second dose for 3 months.
For subsequent use within 5 years: single dose 1 week prior.
General Measures
In most patients, general measures are sufficient owing to the self-limiting nature of acute diarrhea.
Fluid repletion
Oral rehydration with water, salt, and sugar should be sufficient. In some cases fluids used for sweat replacement (eg. Gatorade) may be adequate but it should be noted are not equivalent to oral rehydration solutions. Other options for mild diarrhea include diluted fruit juices with saltine crackers and broth may be more suitable for children as the sugar content is lower.
In cases of severe hypovolemia, IV fluid replacement is typically used for acute management.
Nutrition maintenance and dietary adjustments
In some cases, changes to diet can reduce diarrhea. Note that there is no evidence for probiotic use.
Pharmacotherapy
Antibiotic therapy
In patients with the following, empiric antibiotic use is indicated:
- Severe illness (high-grade fever, hypovolemia, ≥6 loose stools per 24 hrs, severe abdominal pain)
- Features of inflammatory diarrhea (blood, small volume mucous stools, fever)
- High-risk host features
Options for therapy, which can be single-dose or multi-day dosing, include:
- Azithromycin
- Ciprofloxacin or levofloxacin
A stool culture may be used to target specific bacterial causes.
However, in majority of cases, disease is self-limiting and benefit doesn’t outweigh costs.
Symptomatic therapy
In patients with bothersome symptoms who want therapy, and whom fever and bloody stool is absent, loperamide (Imodium) can be recommended. However, caution should be used as antimotility agents can prolong infection or lead to more severe illness. It can also mask dehydration due to water pooling in intestines.