Diarrhea is loose and/or frequent bowel motions. It is not itself a disorder but a symptom of an underlying problem.
Acute diarrhea affects almost everyone from time to time – usually as a result of eating contaminated food or drinking contaminated water. These attacks normally clear up within a day or two with or without treatment. Chronic diarrhea may be the result of a serious intestinal disorder and requires investigation by a doctor.
Diarrhea can be very serious in infants because of the risk of severe, potentially fatal, dehydration. Elderly people are also at risk of dehydration as a consequence of dehydration.
Diarrhea in adults
Normally, the colon (the major part of the large intestine) absorbs much of the water from the liquid food residues that pass through it, producing a semisolid feces. However, if the intestinal contents pass through the colon too quickly, or if the small intestine is inflamed and secretes fluid into the fecal material, diarrhea may result.
Acute diarrhea starts abruptly and usually lasts from a few hours to two or three days. The most common cause is food poisoning. Diarrhea that affects two or more people within six hours of them sharing a meal usually indicates that the food has been contaminated with toxins from Staphylococcus bacteria. Toxins from Clostridium bacteria cause diarrhea within six to 12 hours after eating. If diarrhea develops 12 to 48 hours after eating, it may be due to contamination by bacteria such as Salmonella or Campylobacter, or by a virus such as the rotavirus (see rotavirus infection) or Norwalk virus. Infective gastroenteritis may also be acquired as a result of droplet infection, with adenoviruses or echoviruses, for example. Acute diarrhea may be caused by interference with the intestinal flora (harmless bacteria in the intestine) as a result of travel to a country where these bacteria are of a different type.
Other causes of acute diarrhea include anxiety and, less commonly shigellosis (bacterial dysentery, typhoid fever and paratyphoid fever), drug toxicity, food allergy, and food intolerance. In the case of shigellosis an amoebic dysentery, there may be blood in the feces.
Chronic diarrhea generally takes the form of repeated attacks of acute diarrhea. Causes include Crohn's disease, ulcerative colitis, diverticular disease, colon cancer, thyrotoxicosis, and irritable bowel syndrome. In all of these conditions, except thyrotoxicosis and irritable bowel syndrome, the bowel movements may contain blood.
The water and electrolytes (salts) lost during a severe attack of diarrhea need to be replaced to prevent dehydration. It is possible to buy ready-made powders of electrolyte mixtures to be added to a specific amount of water. Half a liter of the oral rehydration liquid should be drunk every hour, and no solid food eaten, until the diarrhea subsides. Alternatively it is possible to make up an oral rehydration solution: dissolve one teaspoon of salt and eight teaspoons of sugar (which helps the intestine absorb the water and salt) in one liter of water. It is important to be accurate with the quantities as too much salt may cause dehydration.
Antidiarrheal drugs should generally not be taken to treat attacks of diarrhea resulting from infection because they may prolong the illness. However, they may be useful if the diarrhea is disabling or if it is associated with abdominal pain. Examples are codeine phosphate, diphenoxylate, and loperamide.
Diarrhea that recurs, persists for more than a week, or is accompanied by blood in the bowel movements requires investigation by a doctor to discover the underlying cause. In addition to taking the patient's case history, the doctor will probably arrange for a culture of the feces to determine whether or not infection is the underlying cause. If it is not, other tests may be carried, such as X-rays preceded by a barium enema or meal (see contrast medium), sigmoidoscopy, and a biopsy of the rectum. These tests enable the doctor to discover the underlying cause of the diarrhea; treatment will be for that cause.
Diarrhea in infants
Most cases of diarrhea in infants are acute and carry the risk of rapid dehydration (especially when accompanied by vomiting). Dehydration can be fatal unless countered quickly.
The most common cause of diarrhea in infants is gastroenteritis resulting from a viral infection. Babies who are entirely breast-fed are less likely to contract the illness than those who have been bottle-fed. Viral gastroenteritis can damage the lining of the small intestine, thereby impairing its ability to absorb nutrients, and can cause a temporary deficiency of the enzyme lactase. The latter may lead to lactose intolerance (inability to absorb sugar from milk), which may produce secondary diarrhea that can last for several weeks.
An infant with diarrhea should not be fed milk. He or she should be an electrolyte mixture (obtainable from a pharmacy) to replace lost water and salts.
If the diarrhea clears up within 24 hours, milk can be gradually reintroduced over a 24-hour period. The first feeding should consist of one part milk to three parts water, the second of equal parts milk and water, and the third of three parts of milk to one part water, and the fourth of undiluted milk.
A doctor should be called urgently if the infant shows signs of dehydration at any stage during the illness. Signs of dehydration include drowsiness, unresponsiveness, prolonged crying, loose skin, glazed eyes, a depressed fontanelle at the front of the head, a dry, sticky mouth and tongue.