To most individuals, diarrhea means an increased frequency or decreased consistency of bowel movements; however, the medical definition is more exact thanthis. In many developed countries, the average number of bowel movements isthree per day. However, researchers have found that diarrhea best correlateswith an increase in stool weight; stool weights above 300 grams per day generally indicates diarrhea. This is mainly due to excess water, which normally makes up 60-85% of fecal matter. In this way, true diarrhea is distinguished from diseases that cause only an increase in the number of bowel movements (hyperdefecation), or incontinence (involuntary loss of bowel contents).Diarrhea is also classified by physicians into acute, which lasts 1-2 weeks,and chronic which continues for longer than 23 weeks. Viral and bacterial infections are the most common causes of acute diarrhea.

In many cases, acute infectious diarrhea is a mild, limited annoyance. However, worldwide, acute infectious diarrhea has a huge impact, causing over fivemillion deaths per year. While most deaths are among children under five years of age in developing nations, the impact, even in developed countries, is considerable. For example, over 250,000 individuals are admitted to hospitalsin the United States each year because of one of these episodes. Rapid diagnosis and proper treatment can prevent much of the suffering associated with these devastating illnesses. Chronic diarrhea also has a considerable effect onhealth, as well as on social and economic well being. Patients with celiac disease, inflammatory bowel disease, and other prolonged diarrheal illnesses develop nutritional deficiencies, which diminish growth and immunity. They affect social interaction and result in the loss of many working hours.

Diarrhea occurs because more fluid passes through the large intestine (colon)than that organ can absorb. As a rule, the colon can absorb several times more fluid than is required on a daily basis. However, when this reserve capacity is overwhelmed, diarrhea occurs. Diarrhea is caused by infections or illnesses that either lead to excess production of fluids or prevent absorption offluids. Also, certain substances in the colon, such as fats and bile acids,can interfere with water absorption and cause diarrhea. In addition, rapid passage of material through the colon can also do the same. Symptoms related toany diarrheal illness are often those associated with any injury to the gastrointestinal tract, such as fever, nausea, vomiting, and abdominal pain. All or none of these may be present depending on the disease causing the diarrhea. The number of bowel movements can vary--up to 20 or more perday. In some patients, blood or pus is present in the stool. Bowel movementsmay be difficult to flush (float) or contain undigested food material. The most common causes of acute diarrhea are infections (the cause of traveler's diarrhea), food poisoning, and medications. Medications are a frequent and often over-looked cause, especially antibiotics and antacids. Less often, varioussugar free foods, which sometimes contain poorly absorbable materials, causediarrhea. Chronic diarrhea is frequently due to many of the same things thatcause the shorter episodes (infections, medications, etc.); symptoms just last longer. Some infections can become chronic. This occurs mainly with parasitic infections (such as Giardia), or when patients have altered immunity (AIDS). The following are the more usual causes of chronic diarrhea:

  • AIDS
  • Colon cancer and other bowel tumors
  • Endocrine or hormonal abnormalities (thyroid, diabetes mellitus, etc.)
  • Food allergy
  • Inflammatory bowel disease (Crohn's disease and ulcerative colitis)
  • Lactose intolerance
  • Malabsorption syndromes (celiac and Whipple'sdisease)
  • Other (alcohol, microscopic colitis, radiation, surgery).

The major effects of diarrhea are dehydration, malnutrition, and weight loss.Signs of dehydration can be hard to notice, but increasing thirst, dry mouth, weakness or lightheadedness (particularly if worsening on standing), or a darkening/decrease in urination are suggestive. Severe dehydration leads to changes in the body's chemistry and could become life-threatening. Dehydrationfrom diarrhea can result in kidney failure, neurological symptoms, arthritis, and skin problems.

Treatment is ideally directed toward correcting the cause; however, the firstaim should be to prevent or treat dehydration and nutritional deficiencies.The type of fluid and nutrient replacement will depend on whether oral feedings can be taken and the severity of fluid losses. Oral rehydration solution (ORS) or intravenous fluids are the choices; ORS is preferred if possible. A physician should be notified if the patient is dehydrated, and if oral replacement is suggested then commercial (Pedialyte and others) or homemade preparations can be used. The World Health Organization (WHO) has provided this easy recipe for home preparation, which can be taken in small frequent sips:

  • Table salt--3/4 teaspoon.
  • Baking powder--1 teaspoon.
  • Orange juice--1 cup.
  • Water--1 quart or liter.

When feasible, food intake should be continued even in those with acute diarrhea. A physician should be consulted as to what type and how much food is permitted. Anti-motility agents (loperamide, diphenoxylate) are useful for thosewith chronic symptoms; their use is limited or even contraindicated in mostindividuals with acute diarrhea, especially in those with high fever or bloody bowel movements. They should not be taken without the advice of a physician. Other treatments are available, depending on the cause of symptoms. For example, the bulk agent psyllium helps some patients by absorbing excess fluid and solidifying stools; cholestyramine, which binds bile acids, is effective in treating bile salt induced diarrhea. Low fat diets or more easily digestible fat is useful in some patients. New antidiarrheal drugs that decrease excessive secretion of fluid by the intestinal tract is another approach for somediseases. Avoidance of medications or other products that are known to causediarrhea (such as lactose) is curative in some, but should be discussed witha physician.

Prognosis is related to the cause of the diarrhea; for most individuals in developed countries, a bout of acute, infectious diarrhea is at best uncomfortable. However, in both industrialized and developing areas, serious complications and death can occur. For those with chronic symptoms, an extensive numberof tests are usually necessary to make a proper diagnosis and begin treatment; a specific diagnosis is found in 90% of patients. In some, however, no specific cause is found and only treatment with bulk agents or anti-motility agents is indicated.

Proper hygiene and food handling techniques will prevent many cases. Traveler's diarrhea can be avoided by use of Pepto-Bismol and/or antibiotics, if necessary. The most important action is to prevent the complications of dehydration, as outlined above.

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