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This article waslast modified on July 2, 2020.
What is diarrhea?

Diarrhea is a common symptom of a gastrointestinal problem. It is characterized by frequent, loose stools and may be accompanied by stomach (abdominal) pain, cramping, nausea, vomiting, and fatigue. Sometimes there may be blood and/or mucus in the stool.

Diarrhea that lasts one to a few days is considered acute. Most adults experience several mild bouts of uncomplicated diarrhea each year, which are usually acute and end without requiring medical treatment. Diarrhea that lasts two to four weeks or longer is considered chronic. The diarrhea may come and go over this time or may be persistent.

Severe acute diarrhea and chronic diarrhea can be dangerous, especially to very young children and the elderly. When diarrhea is severe or persists for several weeks, it can lead to dehydration and electrolyte imbalance. When levels of electrolytes in the body become too high or too low, it can be life-threatening if untreated. Some individuals affected by diarrhea may require hospitalization. In infants, significant dehydration can occur within a day or two.

Accordion Title
About Diarrhea
  • Common Causes

    There are many infectious and non-infectious causes of acute and chronic diarrhea.

    Common infectious causes of diarrhea:

    Viral, bacterial, and parasitic infections are associated with diarrhea that lasts several days to a few weeks, although some cases may linger – causing chronic diarrhea in those with suppressed immune systems (such as those who have AIDS, cancer, or organ transplants). These sources of diarrhea are infectious, with the virus, bacteria, or parasite shed into the stool and passed from person to person through oral contact with a contaminated surface. Eating food or drinking water that has been contaminated is the most frequent route of infection (food or waterborne illnesses).

    Once someone is infected, the person may pass it on to others around them unless careful sanitation practices (especially thorough hand washing) are followed. This is especially a challenge in households with infected infants, in daycare centers, and in nursing homes. Sometimes an outbreak of bacterial or parasitic infection can be traced back to a particular restaurant or a single food item at a picnic. Sometimes it may be due to a contaminated water source.

    Those who travel outside of the U.S., especially to emerging nations, may be exposed to a variety of disease-causing viruses, bacteria, and parasites. Something as simple as contaminated ice cubes, a fresh fruit salad, or food from a vendor's stall can cause illness.


    • Norovirus, also called Norwalk-like virus is the most common cause of sudden and/or severe illness of the digestive tract (acute gastroenteritis) in the U.S. It is also the leading cause of food and waterborne illnesses, according to the Centers for Disease Control and Prevention (CDC). It is a very contagious virus that can contaminate food and water and also be spread from person to person. Noroviruses may cause outbreaks of gastroenteritis on cruise ships, in nursing homes, schools, the military, and anywhere that people congregate.
    • Rotavirus is the most common cause of severe diarrhea among children. The virus is spread through contact with the stool of an infected person – typically an infant. To prevent contamination, always wash hands after diaper changes and be sure to regularly clean the surfaces of all objects such as the changing table or toys that could be contaminated. Infants can also be given an oral vaccine that is up to 98% effective in preventing rotavirus infections.
    • Other examples of viruses that can cause diarrhea include adenoviruses, hepatitis A, and cytomegalovirus (CMV).

    Bacteria: Bacteria can cause diarrhea by infection or by producing toxins.

    Infection occurs when live bacteria are ingested and begin to grow and multiply in the intestinal tract, producing symptoms. Some bacteria commonly responsible for this type of illness include:

    • Salmonella—often found in raw eggs, raw poultry, and in pet reptiles. Symptoms usually develop within 12 to 72 hours after infection and can last from 4 to 7 days. The infection usually resolves without treatment or with supportive care only, but in some people, such as the very young or elderly, the diarrhea may become so severe that they require hospitalization and prompt treatment with antibiotics. Salmonella serotype Enteritidis and Salmonella serotype Typhimurium are common in the U.S. Many cases are travel-related.
    • Campylobacter—from raw or undercooked poultry, unpasteurized milk or cheese, or contaminated water. Illnesses causing watery and/or bloody stools may develop 2 to 5 days after infection and last about a week. Usually, supportive care is sufficient, but some severe or prolonged cases may require treatment with antibiotics.
    • Yersinia species—found in undercooked pork, seafood, and unpasteurized milk. Infection is frequently associated with 'chitlins,' a dish prepared from intestines of hogs often served during holidays, leading to an increased number of cases in winter. Yersinia enterocolitica is the most common species.
    • Vibrio species—found in contaminated seafood such as raw oysters. Vibrio parahaemolyticus is the most common. Vibrio cholerae is responsible for cholera.

    Some bacteria produce toxins that can cause diarrhea. Examples include:

    • Staphylococcus aureus—common bacteria found on the skin and hair as well as in the noses and throats of many people. It can cause food poisoning when a person contaminates food as it is prepared and then the food is not properly refrigerated or cooked after that. The bacteria produce a toxin that causes sudden and severe symptoms of nausea, vomiting, and diarrhea within several hours of consuming contaminated food.
    • Bacillus cereus—from a variety of foods, especially rice and leftovers that have sat out too long at room temperature; watery diarrhea and cramps can begin 6-15 hours after ingesting the toxin.
    • Clostridium difficile (C diff)—toxins produced by the bacterium Clostridium difficile are often the culprit in antibiotic-related diarrhea. Antibiotic treatment can decrease the normal flora – the "good" bacteria that inhabit the gastrointestinal tract, help digest food, and provide a protective barrier against the "bad" bacteria. When the growth of the normal flora is inhibited, it allows easier access for a pathogen like C. difficile to grow and multiply.
    • Clostridium perfringens—these bacteria may contaminate raw meat and poultry and a person may become infected after eating food that is not cooked, heated, or stored properly. The bacteria form spores that resist high temperatures, so when food that has been cooked cools down, the bacteria can begin to grow. The ingested bacteria produce a toxin that causes an acute infection, with symptoms of intestinal cramping and diarrhea (but no fever or vomiting) that typically develop within 8 to 12 hours, lasting less than 24 hours.
    • Clostridium botulinum—these bacteria cause botulism, a rare but serious disease that is often associated with food that has been improperly handled during the canning process. The bacteria produce a toxin that, in addition to vomiting and diarrhea, can cause muscle weakness, drooping eyelids, blurred vision, double vision, slurred speech, dry mouth, and difficulty swallowing. If left untreated, the disease can progress to cause paralysis of the muscles used for breathing as well as muscles of the trunk, arms, and legs. The toxin is destroyed by high temperatures. One of the most important ways to prevent foodborne botulism is to follow proper home-canning techniques.
    • Shigella—from food and water contaminated with stool; of several species that exist, some produce toxin and cause reactive arthritis and hemolytic uremic syndrome (HUS), a condition associated with red blood cell destruction and kidney failure. Shigella dysenteriae causes dysentery, severe, bloody diarrhea and fever.
    • Escherichia coli 0157:H7 (E. coli)—E. coli are common bacteria normally found in the digestive tract of humans and animals. Most strains don't cause problems, but some produce a toxin, known as the "shiga toxin," that can cause bloody diarrhea and potentially serious infections spread from sources such as undercooked meat, especially hamburger, or from person to person. These are known as shiga toxin-producing E coli or STEC. The very young and the elderly are usually the most severely affected by complications of STEC infections, such as HUS.

    Parasites: The most common parasites in the United States that cause diarrhea are:

    • Giardia species
    • Entamoeba histolytica
    • Cryptosporidium parvum

    These single cell parasites are found in mountain streams and lakes throughout the world and may infect swimming pools, hot tubs, and occasionally community water supplies. Other more worm-like parasites, such as roundworms or tapeworms, may also occasionally cause infections.

    In other parts of the world, especially in developing nations and warm climates, pathogenic bacteria and a much wider range of parasites are frequently encountered. These parasites include flat worms, roundworms, hookworms, and flukes. Visitors usually become infected by eating or drinking something that has been contaminated with the parasites' eggs (ova), but some of the parasites can also penetrate the skin.

    Examples of non-infectious causes of diarrhea:
    Chronic diarrhea, diarrhea that lasts for more than a few weeks, sporadic diarrhea, and diarrhea that alternates with constipation are most frequently associated with non-infectious causes of diarrhea. These may include diarrhea due to:

  • Tests

    Before any diagnostic testing is performed, a healthcare practitioner will want to learn about a person's diarrhea. The frequency, quantity, and consistency of normal bowel movements are very individual. They depend on a person's metabolism, the foods they eat, their activity level, the amount of fluids they drink, the medications they take, and even any stress that they are experiencing. A healthcare practitioner will be looking for things that are out of the ordinary and for alterations that are commonly associated with diarrhea-causing conditions. A healthcare practitioner may ask a series of questions to help make informed choices about which laboratory tests will be the most appropriate, including:

    • What is the frequency of your stools?
    • How long you have been experiencing diarrhea?
    • What are the consistency, color, and approximate volume of the stools?
    • Is there blood or mucus in the stool?
    • What other symptoms are you having: abdominal pain, nausea, fever, headache, fatigue?
    • What and where have you eaten recently?
    • Have you been camping? Have you traveled outside of the U.S.? Where?
    • Are any of your family members, close acquaintances, or co-workers ill?
    • Have you been on antibiotics lately?

    If a person's diarrhea is uncomplicated and goes away within a few days, the healthcare provider may not search for the cause of the gastrointestinal (GI) upset. The healthcare practitioner may order one or more tests, however, if the diarrhea is severe, if there is blood or mucus present, or if it is continuing unabated. This is especially true if the person has been outside the United States and/or has eaten or drunk anything that has also made someone close to them ill.

    Laboratory tests

    Examples of Tests for Infectious Causes of Diarrhea

    Test Sample Description
    Panel of tests for gastrointestinal pathogens Stool Molecular tests that detects specific viruses, bacteria and parasites; the pathogens detected depends on the panel of tests that is used.
    Stool culture Stool Cultures of stool samples use special nutrient media that selectively allow pathogens to grow while inhibiting growth of bacteria that are normally present in the digestive tract (normal flora). They may detect several different bacteria, but laboratories typically evaluate stool cultures for the most common intestinal pathogens:
    • Campylobacter species
    • Salmonella species
    • Shigella species
    Clostridium difficile toxin test Stool Detects toxin produced by C. difficile
    Tests specific for Shiga toxin-producing Escherichia coli (STEC) Stool
    • Toxin test—detects the Shiga toxin directly (used in conjunction with stool cultures)
    • Pulsed-field Gel Electrophoresis (PFGE)—used by public health laboratories to identify subtypes of E. coli that are suspected in an outbreak
    • Genetic tests—rapid molecular tests (PCR) for Shiga toxin 1 gene (stx1) and Shiga toxin 2 gene (stx2)
    Stool WBC Stool Detects white blood cells that may be present in the stool when there is a bacterial infection, such as Clostridium difficile
    Antigen test for rotavirus Stool A rapid antigen test that can detect a common cause of diarrhea in children
    Ova and parasite exam Stool A microscopic evaluation of the stool for parasites and the ova (eggs, cysts) of parasites.
    Antigen tests specific for the parasites:
    • Giardia lamblia
    • Entamoeba histolytica
    • Cryptosporidium parvum
    Stool Detects protein structures on the parasites; they are more sensitive and specific for these particular parasites than the O&P microscopic exam.
    Antibody tests for GI parasites Blood Some reference laboratories may offer these tests. They are not as useful to detect current infections but may be ordered to check for past or chronic infections.

    Examples of Tests for Non-infectious Causes of Diarrhea

    Test Sample Description
    Trypsin/Chymotrypsin Stool Trypsin and chymotrypsin are enzymes that are detectable in the stool if the pancreas is functioning normally. These tests are used to help evaluate pancreatic function. Low levels are seen with pancreatic diseases and cystic fibrosis (CF).
    Stool WBC Stool Increased number of white blood cells in the stool may indicate inflammatory bowel disease (IBD).
    Fecal fat Stool Measures fat level in the stool; increased level is associated with malabsorption that can be caused by celiac disease, pancreatic insufficiency, or cystic fibrosis, for example.
    Food allergy tests Not applicable Oral food challenges are considered the "gold standard" for diagnosing food allergies. They are labor-intensive and require close medical supervision because reactions can be severe, including life-threatening anaphylaxis. Food elimination is another way to test for food allergies: eliminating all suspected foods from the diet, then reintroducing them one at a time to find out which one(s) are causing the problem.
    Celiac disease antibody tests Blood Tissue transglutaminase antibody (tTG), IgA class is the primary test ordered to screen for celiac disease. It is the most sensitive and specific blood test for celiac disease. Other tests may include the IgG class of tTG, total IgA and deamidated gliadin peptide antibodies (anti-DGP), IgA or IgG.
    Lactose tolerance testing Breath, blood Measures hydrogen in the breath or changes in the level of glucose in the blood after a person is given a drink containing a standard amount of lactose, thus determining whether the individual is capable of proper digestion of lactose
    Xylose absorption test Blood, urine Determines how well someone absorbs xylose; it measures the level of xylose in the blood and urine after a standard amount is ingested in order to evaluate the person's ability to absorb carbohydrates in general.
    Lactoferrin and calprotectin tests Stool Detect inflammation associated with IBD
    Anti-Saccharomyces cerevisiae mannan antibodies (ASCA) Blood Detects anti-Saccharomyces cerevisiae antibodies (ASCA), which are immune proteins frequently present in people who have IBD
    Fecal occult blood test and fecal immunochemical test (FOBT, FIT) Stool Detects digestive tract bleeding that may indicate colon cancer
    5-HIAA, Chromogranin A, Serotonin Blood These are tests to help diagnose a carcinoid tumor, which is a relatively rare cause of chronic diarrhea.

    Sometimes a biopsy of the small intestines may be performed to look for signs of parasitic infection, celiac disease, or a tumor.

    Some tests may be done to help check the general health of the individual and/or to help give clues to the cause of the diarrhea:

    • Complete Blood Count (CBC)—may be used to check for anemia, for example, or to help detect an infection. For example, a type of white blood cell called an eosinophil may be elevated with parasitic infections.
    • Electrolytes—if a person is dehydrated, a healthcare practitioner may want to do a blood test to determine whether the person's electrolytes have become imbalanced.
    • Osmolality—blood, urine, or stool samples may be examined to evaluate electrolyte balance.

    Non-laboratory tests
    If the cause of diarrhea is not determined through a physical exam, medical history, or initial testing, special imaging procedures may be used to look at portions of the gastrointestinal tract. See the National Institute of Diabetes and Digestive and Kidney Diseases web site pages on:

  • Prevention

    The best ways to prevent a bacterial, parasitic, or viral gastrointestinal infection are to not drink water or eat food that may be contaminated and to be careful with sanitation measures such as hand washing. Food that might be contaminated, such as raw meats and eggs, should be cooked thoroughly. Cooked foods and foods that are served raw should not touch any surfaces that may have been contaminated.

    If someone in a household has a diarrheal infection, careful hand washing by all family members is recommended. It is best to have the infected person avoid preparing food or drink for others until their infection is over.

    When traveling to developing nations, it is best to drink only bottled water, carbonated drinks, and hot cooked foods. Avoid fresh fruits and vegetables, limited to those that you can peel yourself. Food from food vendors is generally not considered safe.

    There are two vaccines available in the U.S. to protect infants against rotavirus infection. For information, see this CDC's web page. A vaccine is also available to prevent hepatitis A infections. 

    Cases of diarrhea that are caused by foodborne illnesses are monitored on a community and state level. Other than travel-related cases, health officials want to try to determine where the infection came from so that they can address any potential public health concerns. For instance, if someone's infection is due to contaminated food served at a restaurant or due to a contaminated community water supply, then steps will need to be taken to prevent the spread of the infection.

  • Treatment

    Treatment of diarrhea depends on the severity and duration as well as the cause. If diarrhea is uncomplicated and goes away within a few days, no specific treatment and only supportive care may be necessary. Supportive care typically includes drinking plenty of fluids (usually that contain salts and minerals) to avoid dehydration and sometimes modifying the diet. This may involve eating soft, bland foods such as bananas, rice, toast or crackers and avoiding foods that contain caffeine or ones with high fat content.

    If the diarrhea is severe, bloody, contains mucus, and/or has lasted more than two days (24 hours in infants), you should consult your healthcare provider. Tests will be ordered to identify the cause of the diarrhea and then the treatment will be tailored to the cause.

    For viral infections and many pathogenic bacterial infections, the main treatment is to address dehydration to make sure that the person replaces lost fluids and electrolytes. Infants and those with severe dehydration may not be able to drink enough to meet their re-hydration needs and may have to be hospitalized for a short period of time.

    Most bacterial infections of the gastrointestinal tract resolve by themselves in healthy people. In some cases, antibiotics actually prolong the shedding of the pathogen and may lead to carrying the organisms for months ("carrier state"). People with underlying diseases that compromise the immune system, such as cancer, may be treated with antibiotics since they may not be able to clear the infection on their own.

    Most parasitic infections are treated, although a few may resolve on their own. With some bacterial and parasitic infections, a healthcare practitioner may treat the entire family even if only one member is obviously affected.

    People should talk to their healthcare provider before taking an over-the-counter anti-diarrhea medicine. Diarrhea is one of the methods that the body uses to help rid itself of the infection. Anti-diarrhea medication can slow down or prevent this from happening, potentially prolonging the length of the illness and sometimes making the infection worse.

    Non-infectious causes
    Treating non-infectious causes of diarrhea may be less straightforward and more difficult than infectious causes. It may involve treating the underlying condition once it is identified. It may require diet adjustments, long-term treatment or ongoing nutritional support. For diarrhea caused by food sensitivities or intolerances such as lactose intolerance, for example, treatment often involves avoidance of the suspected cause. A diagnosis of celiac disease may require avoidance of all foods containing gluten.

For Health Professionals - Optimal Testing: Stool Reducing Sugars

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**This content is intended for healthcare professionals.**

Visit the article For Health Professionals: Stool Reducing Sugars for the full recommendation.

Recommendation: The test for stool reducing sugars should only be ordered in children with short bowel syndrome to differentiate the source of diarrhea.

The content for Optimal Testing: AACC's Guide to Lab Test Utilization has been developed an approved by the AACC Academy and AACC's Science and Practice Core Committee.

View sources

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