Acute diarrhea is one of the most commonly reported illnesses in the United States. Diarrhea is considered acute when it lasts less than two weeks. Diarrhea that lasts between two and four weeks is called persistent diarrhea, and diarrhea lasting longer than four weeks is considered chronic.
Some people think that diarrhea is just an increase in the number of stools, or just stools that are loose or watery, but it is actually a combination of both: loose or watery stools that occur more than three times per day. Other symptoms that often accompany diarrhea include abdominal cramps, fever, nausea, vomiting, fatigue, and bowel movement urgency. Chronic diarrhea can also cause weight loss and malnutrition.
Most cases of acute diarrhea are caused by viruses. This is called viral gastroenteritis. In children, the most common diarrhea-causing virus is rotavirus. In adults, norovirus is most commonly responsible for acute diarrhea.
Chronic diarrhea can be the result of a number of conditions. Some conditions cause the intestines to secrete extra water or fluid, and others prevent the intestine from absorbing normal water and fluids, thus leading to diarrhea. When chronic diarrhea is bloody, it may be due to an inflammatory bowel disease, or IBD, such as ulcerative colitis or Crohn's disease. Less common causes include radiation therapy, colon cancer or polyps, and ischemia of the gut, or intestines. Infections do not usually lead to chronic diarrhea unless the infection is due to a parasite.
Chronic diarrhea that is considered fatty or malabsorption diarrhea is usually due to low pancreatic enzyme levels or small bowel disease. Low pancreatic enzyme levels, which may be caused by chronic pancreatitis, affect the body's ability to digest fats, so as the fats travel through the intestines, they take water with them. Small bowel diseases, such as celiac disease and Crohn's disease, affect the small intestine's ability to absorb fat and other nutrients, and have a similar effect.
Another cause of chronic diarrhea is intolerance of certain food products, such as lactose, fructose, and sorbitol. If the body doesn't absorb one of these substances, then water follows along with it in the intestines. Certain medications, such as antibiotics, antacids, antihypertensives, and nonsteroidal anti-inflammatory drugs, or NSAIDs, can also cause diarrhea by other mechanisms.
Most cases of acute diarrhea resolve quickly on their own, but drinking plenty of fluid with sugar and salt can help prevent dehydration. Salt and sugar together help the intestine absorb fluids. Milk and dairy products can make diarrhea worse, so they should be avoided until the acute diarrhea episode has passed.
Severe symptoms of diarrhea can be treated with medications, such as bismuth subsalicylate or loperamide, the latter of which can slow the intestines. However, if diarrhea is bloody or accompanied by high fever, these medications should be avoided because they can make the illness worse by slowing the diarrhea. Some cases of diarrhea caused by infection may be treated with antibiotics, but in other cases antibiotics need to be avoided.
Treatment of chronic diarrhea depends on the cause, but antimotility agents such as loperamide may be used to reduce symptoms. Because chronic diarrhea can cause nutritional deficiencies, treatment may include replacing certain minerals and vitamins, such as calcium, potassium, magnesium, and zinc.