• Basics

    Diarrhea is a condition characterized by frequent, loose, watery stools. Mild cases typically last three to seven days, and resolve without treatment. The average adult experiences four episodes of diarrhea a year. Infants and children may also develop diarrhea; in the U.S., most children have had 7 to 15 episodes of diarrhea by the time they reach 5 years of age. Chronic diarrhea is recurrent, or lasts for more than three weeks, and usually requires medical attention.

    Diarrhea occurs when your body's ability to absorb liquid from digested food particles is disrupted. In patients with diarrhea, loss of water and electrolytes may result in dehydration, which is a major concern. The most important treatment for simple cases of diarrhea is to prevent dehydration, and to rehydrate if you have already become dehydrated.

    Worldwide, diarrhea is one of the greatest threats to the lives and health of children. More than one billion cases occur each year, and three to five million children die of diarrheal infections. Although deaths from diarrhea are rare in the U.S. and other developed countries, the condition is responsible for several million visits to doctor's offices and numerous hospital stays each year.

    Diarrhea is sometimes called "stomach flu" or gastroenteritis. Diarrhea may be accompanied by vomiting. It may occur in clusters among schools, neighborhoods, or families because the infection spreads through close contact. These mini-epidemics usually clear up quickly.

    People of all ages are vulnerable to traveler's diarrhea. When you travel, particularly to developing countries, a variety of new organisms are introduced into your system. Some of these organisms may be infectious, and may cause diarrhea. Traveler's diarrhea is most common in areas that have contaminated water supplies, poor sewage systems, and inadequate techniques of food handling or preparation.

    Although patients recognize diarrhea mainly by the frequency of loose stools, doctors may define it as a significant increase in the weight of stool passed in a single day. In medical terms, diarrhea is defined as more than 200 g (or 200 mL) of stool over a 24-hour period in persons consuming a typical Western diet. Your doctor may use this definition when making a diagnosis. However, he or she will also take into account your explanation of your symptoms.

  • Causes

    Several agents can cause diarrhea, including viral, bacterial, or parasitic infections resulting from consuming contaminated food or water. You can also pick up an infectious agent through personal contact with an infected person. Common bacterial causes of infection include Salmonella species, Shigella species, Escherichia coli, and Campylobacter jejuni. Because only a few bacteria are needed to cause Shigella infections, they spread easily in day care centers, institutions, and families. E. coli bacteria can cause diarrhea by attacking the intestinal wall or by producing toxins that block the ability of the intestine to absorb water and electrolytes. Some of the toxins produced by bacteria may even make the intestine secrete water and electrolytes instead of absorbing them. A serious form of E. coli has caused recent nation-wide food outbreaks, leading to several deaths.

    Several viruses, including rotavirus or the Norwalk virus, can lead to diarrhea. These viruses damage the mucous membrane that lines your intestines, and disrupt fluid absorption. Rotavirus is a common cause of diarrhea in U.S. children. In fact, most children in the U.S. have had a rotavirus infection by the time they are four or five years old, although they may not necessarily have shown symptoms. Rotavirus tends to spread in such settings as daycare centers. In adults, the Norwalk virus is more commonly the cause of diarrhea. The Norwalk virus can be found in drinking water, or in food such as contaminated shellfish. Norwalk virus has been known to lead to outbreaks on cruise ships. Other viruses that may trigger diarrhea include cytomegalovirus, herpes simplex virus, and viral hepatitis.

    Parasites that enter the body and invade the digestive system can cause diarrhea. The most likely "bugs" are Giardia lamblia, Entamoeba histolytica, and Cryptosporidium species. In the U.S., Giardia infection is the most common parasitic cause of diarrhea. Giardia spreads through contaminated water supplies, and can be passed among children in day-care centers.

    Enterotoxigenic E. coli, an organism that is part of the E. coli species of bacteria, is the most common cause of traveler's diarrhea. Shigella species and many other pathogens also cause this disease among travelers from industrialized countries. Rotavirus, the Norwalk virus, other viruses, and such parasites as Giardia species and Entamoeba histolytica, are responsible for some cases. There is no evidence that jet lag, change in altitude, or fatigue contribute to traveler's diarrhea.

    The inability to digest certain food substances, such as lactose (the form of sugar found in dairy products), wheat, or other grains, can also cause diarrhea; chronic diarrhea can be caused by food allergies or food additives, such as sorbitol and fructose.

    Diarrhea can be caused by a reaction to medication. Many medications can cause diarrhea, but antibiotics, some blood pressure medications, chemotherapy drugs, and antacids containing magnesium are the most common. Other medications that may cause diarrhea include digitalis (used to treat heart disease), diuretics (used to treat high blood pressure and edema), cholesterol-lowering agents, lithium (used to treat bipolar disorder), theophylline (used to treat respiratory disorders, especially asthma), thyroid hormone, and colchicine (used to treat gout). Chronic diarrhea is most likely to be caused by antibiotics, drugs for high blood pressure, and cancer medications.

    A range of diseases can also lead to diarrhea. Intestinal diseases such as inflammatory bowel disease (including ulcerative colitis or Crohn's disease) or celiac disease (the inability to digest wheat and sometimes other grains), are one category. Diseases that affect the body's glands (the endocrine system) can also cause diarrhea. Some examples are thyroid disease, diabetes, adrenal disease, and Zollinger-Ellison syndrome, a tumor of the pancreas that causes ulcers in the upper gastrointestinal tract. Diseases that interfere with intestinal function, such as irritable bowel syndrome, can also cause diarrhea. Acute and chronic diarrhea may be side effects of HIV infection or AIDS. People who recently received an organ transplant may be at higher risk for diarrhea.

    Several surgical procedures can cause diarrhea because they affect the movement of food through the digestive system. If part of your intestine has been removed, you may develop short-bowel syndrome. In this syndrome, the shorter intestine is unable to absorb all of the food you eat. Gallbladder and stomach surgery can also cause diarrhea.

    Possible causes of diarrhea include such toxins as insecticides, psychedelic mushrooms, arsenic, and overuse of alcohol or caffeine.

    The causes of acute and chronic diarrhea cannot always be identified. If the problem clears up in a few days, it is usually not necessary for you or your provider to search extensively for its source. Acute diarrhea can progress to chronic diarrhea if improperly treated.

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