Diarrhea: Definition, Impact, and Risks

Study Notes

Diarrhea is defined as the passage of abnormally liquid or unformed stools at an increased frequency.
For adults on a typical Western diet, stool weight greater than 200 g/day is considered diarrhea.
Acute diarrhea is characterized by a duration of less than 4 weeks.

The World Health Organization (WHO) estimated 4.6 billion episodes of diarrheal illness worldwide annually.
Diarrheal diseases are among the five leading causes of death globally and are the second leading cause of death in children under five years of age.
Over 90% of acute diarrhea cases are caused by infectious agents.
Most cases of diarrhea are linked to contaminated food and water sources.
Globally, approximately 2.4 billion people lack access to basic sanitation facilities.

Crowded environments and poor sanitation (e.g., daycares, institutions, refugee camps)
Unplanned urban settlements
Direct contact with an infected individual
Immune suppression (e.g., AIDS, chemotherapy)

Shigella dysenteriae and Vibrio cholerae are commonly associated with epidemic diarrhea.
There are four Shigella species that cause bloody diarrhea, distinguished by serology: S. dysenteriae, S. flexneri, S. boydii, and S. sonnei.
S. dysenteriae serotype 1 (Sd1) is uniquely responsible for epidemic dysentery.

In non-epidemic situations, enterotoxigenic Escherichia coli is the most frequent cause of acute watery diarrhea.
Globally, Shigella species, especially S. flexneri, are the primary causes of acute bloody diarrhea.

Watery diarrhea is typically non-bloody, while dysentery is characterized by diarrhea with visible blood.
These clinical features can differentiate cholera (watery diarrhea) from epidemic dysentery due to S. dysenteriae serotype 1 (Sd1), which is significant for therapeutic and public health considerations.
"Rice-water" appearance of stool with mucus is suggestive of cholera.
Diarrhea caused by V. cholerae can present abruptly with vomiting and abdominal cramping, but usually without severe pain or tenesmus.
Fever is uncommon in cholera.
Shigellosis is typically characterized by frequent passage of small liquid stools containing visible blood, with or without mucus.
Abdominal cramps and tenesmus are common, along with fever and anorexia.
The specific infectious cause cannot be determined based solely on signs or symptoms.

The initial evaluation of adults with acute diarrhea should include a thorough history and physical exam to assess the type of diarrhea and severity of hypovolemia.

The physical exam should focus on determining the degree of volume depletion (hypovolemia).
Early hypovolemia: signs and symptoms may be absent.
Moderate hypovolemia: thirst, restless or irritable behavior, decreased skin turgor (tenting), sunken eyes.
Severe hypovolemia: diminished consciousness, lack of urine output, cool moist extremities, rapid and feeble pulse, low or undetectable blood pressure, peripheral cyanosis.

No dehydration: normal appearance and behavior.
Some dehydration: eager to drink, irritable, skin pinch returns slowly.
Severe dehydration: unable to drink, lethargic or unconscious, skin pinch returns very slowly.