Diarrhea
| January 1, 2008
In-Depth Report
Diarrhea
Most everyone has had a bout of the runs from eating tainted food or drinking unclean water. But some people experience the frequent, runny bowel movements of diarrhea for no apparent reason. Although diarrhea can accompany a number of GI disorders, both functional and organic, it may occur on its own, intermittently or constantly, for any of several reasons.
What is diarrhea?
Diarrhea is sometimes defined as having more than three bowel movements a day. But a more widely accepted definition of diarrhea is liquid or watery stools. When diarrhea occurs more than three-quarters of the time and lasts at least three months without an identifiable cause, the diarrhea is said to be functional.
Diarrhea is the body's response to something that upsets the intestines; it's the body's way of clearing out whatever is causing the upset. Sometimes you know exactly what caused the intestinal distress — for example, bacterial contamination in food. Other times, it remains a mystery.
In most cases, the problem will clear on its own, and you may not need to call a doctor. Diarrhea usually isn't serious, but it can lead to dehydration and weight loss. And while everybody experiences diarrhea sometimes, for a significant percentage of the population, the condition is persistent. Cases that don't clear up in a few days — that is, chronic or functional cases — require a doctor's care.
Causes of diarrhea
Normal defecation depends on the small intestine, colon, rectum, and anal sphincter working normally. In diarrhea, something goes wrong.
The small intestine usually handles about 8 liters of fluid from food and pushes about 1 liter to the colon. The colon absorbs most of this fluid and moves the compacted residue, which contains a few ounces of water, to the rectum. The rectum can store up to 200 grams of stool before defecation is triggered. However, any interference with this process can cause the colon to be overwhelmed by the fluid load, resulting in diarrhea. In fact, any disturbance in the colon that interferes with the packing, storage, or dehydrating of the stool can result in diarrhea.
Diarrhea may be caused by viruses, bacteria, or parasites, as well as by various foods, drugs, and medical conditions or treatments.
Viruses. A wide variety of viruses can cause diarrhea (viral gastroenteritis). Among them are rhinovirus or adenovirus, rotavirus (the most common cause of diarrhea in infants), influenza, and norovirus (the most common cause in adults). Most cases are not caused by viruses, although many of the most severe cases are.
Bacteria. A number of bacteria are associated with diarrhea. Shigella, Vibrio cholerae, and Escherichia coli produce toxins that cause diarrhea, while salmonella and campylobacter invade the stomach lining and produce inflammation and diarrhea. Food poisoning is usually due to bacterial contamination of food.
Parasites. Intestinal parasites, such as Giardia intestinalis, Cryptosporidium parvum, and roundworms or tapeworms, may cause diarrhea. These parasites are often found in untreated or contaminated water. Drinking untreated water from a lake or stream while camping is a common way to pick up Giardia parasites.
Diseases of the bowel. Crohn's disease and ulcerative colitis, two forms of inflammatory bowel disease, can cause diarrhea (see "Irritable bowel syndrome: What else could it be?").
Immune deficiency. Patients suffering from diseases such as AIDS or those who are undergoing treatments that weaken the immune system and damage the lining of the intestine, such as chemotherapy, may also suffer from severe diarrhea.
Stress. Emotions are known to wreak havoc on the bowels in a number of ways. Diarrhea is a common complaint of persons under severe stress or emotional upset.
Foods. Certain foods, even if perfectly fresh, can cause diarrhea in some people. Among them are fruits, beans, and coffee. For most people, unripe fruits or any type of spoiled food will cause diarrhea, as will the particular foods that a person cannot tolerate, such as milk products for those who are lactose intolerant.
Medications. A number of drugs, available by prescription and over the counter, can cause diarrhea as a side effect. The most common culprits include antibiotics, antacids containing magnesium, and some blood pressure and heart medications. Because antibiotics kill some of the naturally occurring GI bacteria, the gut becomes more vulnerable to attack by Clostridium difficile, a bacterium that produces toxins that can cause diarrhea. In 2005, the Centers for Disease Control and Prevention reported the emergence of a new, more virulent strain of C. difficile that causes more serious — and more often deadly — disease. This strain is not as responsive to treatment with the antibiotic metronidazole, which is normally a first-line therapy for C. difficile -associated diarrhea.
Do you have diarrhea?According to the Rome III criteria for a diagnosis of diarrhea, patients must have experienced the following for the past three months, with symptoms starting at least six months before diagnosis: loose (mushy) or watery stools without pain occurring in at least three-quarters of stools. |
When to call the doctor
If your diarrhea lasts three days or more, it's time to call the doctor. However, call immediately if there is blood in the stool or if the stool looks like black tar. The same goes for diarrhea accompanied by a fever over 101° F, severe abdominal or rectal pain, and severe dehydration (dry mouth, wrinkled skin, or lack of urination). Weight loss of more than 5 pounds is also a reason to see a doctor.
Chronic diarrhea may be an indication of irritable bowel syndrome, and your doctor may want to evaluate you for that condition. There are forms of chronic diarrhea that have nothing to do with food but are the result of fluids secreted by the intestine. These are called secretory diarrheas and may rarely be caused by hidden tumors, sometimes in the pancreas, that release chemical messengers telling the bowel to release large amounts of liquid. Microscopic colitis is a more common cause of secretory diarrhea. In this case, the colon looks normal during a colonoscopy, but biopsies show intense inflammation of the colon lining.
Diagnosing diarrhea
The doctor will ask questions about your symptoms and try to determine whether the diarrhea is chronic, or whether it's the result of a virus or bacterium and thus likely to be short-lived. If it's chronic, the doctor will want to probe further to establish whether the diarrhea is due to an organic problem or whether it's functional. You may be asked questions about your habits, including drug or alcohol use. Alcohol abuse commonly results in diarrhea, for example, as does use of certain drugs, including cocaine.
The doctor will probably ask questions such as these:
When did the diarrhea start?
Have any other family members been sick?
Have you recently traveled out of the country?
Are you having abdominal pain? Fever? Chills?
Is there blood in the stool?
Is it worse when you are under stress?
Do any specific foods make it worse?
Do you drink coffee? Alcohol?
What medications are you taking or have you taken recently?
If blood or pus in the stool accompanies diarrhea, or if there is fever, anemia, profound loss of appetite, or severe vomiting, it's not functional diarrhea.
For most people and for most mild episodes of diarrhea, no specific lab tests are required. But for more severe cases, or when symptoms of inflammation are present, the doctor will order stool tests to look for the presence of certain bacteria.
Blood can be drawn to test for hemoglobin, white cell count, and sedimentation rate. A sigmoidoscopy may also be performed. For people over 40, a colonoscopy or a barium enema may be ordered to check for organic diseases. Doctors must exclude the possibility of Crohn's disease, ulcerative colitis, or other serious illness, such as colon cancer. These are usually accompanied by blood in the stool, fever, or weight loss.
Treating diarrhea
Most people with acute diarrhea will recover on their own; it generally runs its course in a few days. In particularly severe or prolonged episodes, replacement of lost fluids and electrolytes (such as sodium and potassium) is essential to combat dehydration. Clear liquids are the first choice. For mild cases of dehydration, juices, soft drinks, clear broth, and safe water are recommended. Apple juice and sodas are good. Citrus juices are not. Neither are alcoholic beverages.
For more severe cases, sports drinks like Gatorade can replace sugars and electrolytes, but too much may cause further diarrhea. Rehydration solutions such as Pedialyte are probably best, particularly for children with diarrhea.
Products such as kaolin and pectin (Kaopectate) give the stool a firmer consistency. Medications that work to slow the bowel include paregoric, opiates, and diphenoxylate with atropine (Lomotil), all of which are available by prescription only, as well as loperamide (Imodium), which is available over the counter. These provide quick but temporary relief by reducing muscle spasms in the GI tract. They should be used only for a few days, however. Bismuth subsalicylate (Pepto-Bismol) also seems to work pretty well; it may turn the stool and tongue black, so don't be alarmed if that happens.
Be aware, however, that using these remedies for symptomatic relief is controversial, particularly for some types of bacterial gastroenteritis. While they may make you more comfortable, they suppress the diarrhea that helps cast the offending bacteria out of your system. If you slow down the process, the bugs stay in your system longer.
After the first 24 hours, a little food is probably okay. But it may be best to try to go without food as long as possible. If you are really hungry, try going on a BRAT diet: bananas, rice, applesauce, and white toast. The bananas bind the stool, slowing the movement a little. The rice, applesauce, and dry toast are low in fiber and easily digested.
Preventing diarrhea
Preventing diarrhea is largely a matter of luck and common sense. If certain foods give your intestinal tract a hard time, stay away from them. Many cases of diarrhea are caused by intestinal bugs, but if yours seems to be functional and not connected with bacterial infection, try to assess what conditions seem to trigger it and, in particular, whether stressful situations seem connected. Take steps to reduce stressful situations (see "The Stress Connection") and ask your doctor about medications that might treat functional diarrhea.
General rules for avoiding diarrhea caused by bacterial infections include washing all fruits and vegetables well and making sure they're ripe when you eat them. Rinse chicken before you cook it, and cook chicken and other meats thoroughly. Clean all food preparation areas such as countertops and cutting boards with soap and warm water. Wash your hands thoroughly before and after handling food.
Be careful about eating foods left outside for long periods of time — at barbecues or picnics, for example. Bacteria can grow easily in the warm air. And don't take leftovers home from these events. Even inside, leftovers should be refrigerated quickly after the meal has been served.
Review Date: 2008-01-01
Harvard Medical School does not endorse products or services.
