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Scope of the problem
There are estimated to be over 100 million cases of acute diarrhea in adults in the US each year. Diarrhea accounts for approximately 5% of emergency department (ED) visits. This complaint is even more common in children <3 years of age. Worldwide, diarrheal illnesses affect 3 to 5 billion people a year, accounting for over 5 to 10 million deaths in developing countries. Etiologies range from benign conditions such as viral gastroenteritis to life-threatening invasive diarrheal illnesses. The most common causes of acute diarrhea are infectious agents.
Diarrhea is defined as the rapid passage of excessively fluid stool, passing stool that takes form of the container rather than remaining in its natural form, or frequency of stool greater than three times a day. The gastrointestinal (GI) tract resorbs over 9 liters of fluid a day (the majority by the small intestine), leaving approximately 100ml/day excreted in stool. Alteration in this process may lead to diarrhea. This can occur from an increase in the volume load presented to the GI tract, diminished ability to resorb fluids by the bowel, inflammatory processes, or an increase in gut motility.
Osmotic diarrhea occurs when unabsorbable or poorly absorbable molecules such as lactulose and laxatives challenge the small intestine. Inflammatory diarrhea occurs with inflammation of bowel mucosa, which limits its ability to resorb fluid. This can occur with numerous agents, for example Shigella and Giardia.