You are most likely to come down with diarrhea after coming into contact with these infectious organisms and agents:

• A virus, such as rotavirus, Norwalk agent, enterovirus, or a hepatitis virus.
• A bacterium, such as E. coli, salmonella, shigella, clostridium, or Vibrio cholerae.
• A parasite, such as those that cause giardiasis and amebiasis.

You may pick up an infectious agent from contact with another individual who has it, or you may get it after eating contaminated food or drinking contaminated water. If you eat food that was improperly cooked or was contaminated after cooking, you may get food poisoning, which can lead to diarrhea. Children who attend day care and their families are more likely to be exposed to certain infectious agents.

Many people who travel to foreign countries develop what is termed "traveler's diarrhea," usually after drinking contaminated water. Infectious diarrhea is a particular hazard in developing countries where it may be difficult to keep waste water and sewage separate from water used for cooking, drinking, and bathing and where inadequate facilities make it difficult to practice good personal hygiene.

Other Medical Conditions

A number of noninfectious medical conditions may cause diarrhea, too. These include:

• Inability to digest certain foods, including a lactose intolerance (difficulty digesting sugar found in dairy products); celiac disease (inability to digest wheat and sometimes other grains); and pancreatic problems, such as those caused by cystic fibrosis, which interfere with production of important digestive substances.
• Surgery to remove part of your small intestine. A shortened small intestine may be unable to absorb all the substances you eat. This is referred to as short-bowel syndrome.
• Surgery after removal of the gallbladder. An increase in bile in the colon may result in watery stools.
• Certain diseases of the endocrine (hormonal) system, including overactive thyroid disease, diabetes, adrenal disease, and Zollinger-Ellison syndrome.
• Certain rare tumors (including carcinoid tumor and pheochromocytoma) that produce diarrhea-causing substances (hormones).
• Inflammation in the intestinal tract, which can result in chronic diarrhea. If you have inflammatory bowel disease (such as ulcerative colitis or Crohn's disease), you will have regular bouts of diarrhea during a flare-up of your disease. Sometimes, people who develop bumps in their intestine from diverticulitis also get diarrhea.
• Irritable bowel syndrome, which may cause alternating bouts of diarrhea and constipation.

Medications and Other Substances

Many medications can cause diarrhea. Some of the most common include antacids containing magnesium, laxatives, digitalis, diuretics, a number of antibiotics, chemotherapy drugs, cholesterol-lowering agents, lithium, theophylline, thyroid hormone and colchicine.

Radiation therapy for prostate cancer or cancers in the abdomen can damage the intestine and cause diarrhea.

Toxins such as insecticides, psychedelic mushrooms, and arsenic can cause diarrhea, and overuse of caffeine or alcohol may contribute to diarrhea.

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