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Chapter 31



Most cases of diarrhea are self-limited and require only supportive care. Conversely, patients with more serious infection and associated comorbidity may have life-threatening dehydration and shock. Associated sepsis and septic shock can be complications of severe diarrheal disease. Numerous but relatively rare, noninfectious causes of diarrhea should be considered.


Worldwide, diarrhea remains a major health problem, accounting for approximately 4% of all deaths each year, which is estimated by the World Health Organization (WHO) to be 2.2 million victims.1 A large proportion of these deaths occur in small children in developing countries. Diarrheal disease kills 1.5 million children every year.1 Globally, there are about 2 billion cases of diarrheal disease every year.1

Rotavirus causes 25 to 65% of childhood-associated diarrheal illnesses (3.5 million cases per year in the United States), whereas adults experience 74 million episodes of diarrhea annually. In the United States, 90% of diarrheal illnesses are caused by noroviruses (caliciviruses), of which more than 100 different strains are recognized.24 Patients at the extremes of age, those with significant comorbidity, those who are immunologically compromised, and those with iatrogenic illness are most vulnerable to significant morbidity and mortality. An estimated 60% of patients infected with human immunodeficiency virus (HIV) experience significant diarrhea during the course of their illness.5

Natural disasters, environmental changes, and wars or political uprisings can result in mass migrations of refugees to neighboring countries. This can lead to starvation and thirst in areas with limited resources, a setup for water contamination and epidemic diarrhea. As witnessed in Haiti after the 2010 earthquake, lack of clean water and poor sanitation led to an epidemic of a deadly form of Vibrio cholera.6 Most adults experience diarrhea many times during their lifetime. Diarrheal illnesses are the primary cause of many hospitalizations and hours of lost work.

Definition and Categorization

The term diarrhea is derived from the Greek words dia (“through”) and rhein (“to flow”). The two main categories of diarrhea-associated illness are infectious and noninfectious. Infectious causes represent about 85% of cases, whereas noninfectious causes account for only 15% of the total. Infectious diarrhea may be divided into viral, bacterial, and parasitic causes (Box 31-1), with estimates of their relative contributions being 70% for viral, 24% for bacterial, and 6% for parasitic infections.7

BOX 31-1   Causative Agents of Infectious Diarrhea

Viral (60% of Cases)

Bacterial (20% of Cases)

Parasitic (5% of Cases)

HIV, human immunodeficiency virus.

*Associated with fever, abdominal pain, and fecal red blood cells or white blood cells. % indicates the estimated contribution to total cases.

Definitions for diarrhea have been proposed to standardize nomenclature, help the clinician determine a probable cause, and direct empirical therapy if indicated7:

Acute diarrhea presentations usually will be infectious. A majority of these cases are self-limited and caused by viral and bacterial pathogens. Persistent diarrhea suggests an enteric pathogen other than viral, such as bacterial or protozoan. Chronic diarrhea usually is associated with noninfectious causes and requires further testing to determine the cause.

Normally, the small and large bowels absorb 99% of gastrointestinal tract secretions produced and liquids ingested each day. Any pathologic state that reduces water absorption by 1% can cause diarrhea.8 Diarrhea results from one or more of four different pathologic processes that are characteristic of the primary cause and that contribute to the decreased absorption of the gut.

Secretory diarrhea is caused by pathogens that produce cytotoxins that increase cellular permeability and cause the oversecretion of water and electrolytes. Most cases of diarrhea encountered in the emergency department (ED) are secretory. Noninfectious causes of secretory diarrhea include medications, toxic substances, endocrine disorders, and neoplasias (Box 31-2).

BOX 31-2   Causes of Noninfectious Diarrhea