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What is diarrhea?

Diarrhea is a common symptom of a problem with the digestive tract. It is marked 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. Persistent diarrhea lasts longer than 2 weeks and less than 4 weeks. Diarrhea that lasts 4 weeks or longer is considered chronic. The diarrhea may come and go over this time or may be constant.

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


About Diarrhea

Infections That Cause Diarrhea

Viral, bacterial, and parasitic infections can cause diarrhea that lasts several days to a few weeks, although some cases may linger – causing chronic diarrhea in those with suppressed immune systems (e.g., people with HIV/AIDS or cancer, or organ transplant recipients). These sources of diarrhea are infectious, as the virus, bacteria, or parasite are shed into the stool and can be 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 you are infected, you can pass it on to others around you unless you follow careful sanitation practices (especially thorough hand washing). 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.

People 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).


Infection can occur when you eat or drink something contaminated with live bacteria and they begin to grow and multiply in your intestinal tract, producing symptoms. Some bacteria commonly responsible for this type of illness include:

  • Salmonella—often found in raw eggs, meat, poultry and seafood, and in pet reptiles. Symptoms usually develop within 6 hours to 6 days 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. Two of the most common species in the U.S. are Salmonella enterica serotype Enteritidis and Salmonella enterica serotype Typhimurium. Many cases are related to travel.
  • Campylobacter—from raw or undercooked poultry, unpasteurized (raw) milk or cheese, contact with animals, 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 raw or undercooked pork, seafood, and unpasteurized milk. Infection is frequently associated with ‘chitlins,’ a Southern dish prepared from pork intestines often served during holidays, leading to an increased number of cases in winter. Yersinia enterocolitica is the most common species.
  • Vibrio species—found in raw or undercooked shellfish, such as raw oysters.Vibrio parahaemolyticus is the most common species found in the U.S. 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 if food is contaminated and not properly refrigerated or cooked. The bacteria produce a toxin that causes sudden and severe symptoms of nausea, vomiting, and diarrhea within 30 minutes to 8 hours of eating 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 this type of bacteria are often the cause of diarrhea related to use of antibiotics. Antibiotic treatment can decrease the normal flora – the “good” bacteria that inhabit the digestive tract, help digest food, and provide a protective barrier against the “bad” bacteria. When the growth of the normal flora is inhibited, C. difficile grows and multiplies more easily.
  • 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—a bacteria found in diarrhea that is easily spread from person-to person by getting germs on their hands and then touching their food or mouth, consuming contaminated food or water. Of the 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.” These are 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. It can cause bloody diarrhea and potentially serious infections spread from contaminated food sources such as undercooked ground beef, leafy greens, or from personal contact.

Parasites: The most common parasites in the U.S. 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 worm-like parasites, such as roundworms or tapeworms, may also occasionally cause infections.

In other parts of the world, especially in resource-poor nations and warm climates, pathogenic bacteria and a much wider range of parasites cause illness. These parasites include flat worms, roundworms, hookworms, and flukes. Infections are usually caused 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 4 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:


Before any diagnostic testing is performed, a healthcare practitioner will want to learn about your diarrhea. The frequency, quantity, and consistency of normal bowel movements are very individual. They depend on metabolism, diet, activity level, the amount of fluids you drink, medications, and even stress. A healthcare practitioner may ask a series of questions to help make informed choices about which laboratory tests will be the most appropriate, such as:

  • What is the frequency of your stools?
  • How long you have been experiencing diarrhea?
  • What is 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 your diarrhea is uncomplicated and goes away within a few days, your healthcare provider may not order any testing. However, your healthcare practitioner may order one or more tests if the diarrhea is severe, if there is blood or mucus present, or if it is persistent. This is especially true if you have been outside the U.S. and/or have eaten or drunk anything that has also made someone close to you ill.

Laboratory Tests

Examples of Tests for Infections That Cause Diarrhea

Test Sample Description
Gastrointestinal pathogens panel Stool A panel that looks for multiple pathogens, including viruses, bacteria and parasites
Stool culture Stool Cultures of stool samples are used to grow any pathogenic bacteria that may be present. The most common include:

  • 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 microscope is used to look for parasites and the ova (eggs, cysts) of parasites in a stool sample.
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 parasites than the ova and parasite 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
Chymotrypsin Stool 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, but they require close medical supervision because reactions can be severe (e.g., anaphylaxis). Food elimination: 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. Other tests may include tTG, IgG, total IgA and deamidated gliadin peptide antibodies (anti-DGP), IgA or IgG.
Lactose tolerance testing Breath, Blood Helps determine whether you are able to digest lactose properly
Xylose absorption test Blood, Urine Determines how well you absorb xylose; evaluates your ability to absorb carbohydrates in general
Lactoferrin and calprotectin tests Stool Detect inflammation associated with IBD
Anti-Saccharomyces cerevisiae antibodies (ASCA) Blood Detects ASCA that are 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 Used to help diagnose a carcinoid tumor, 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 laboratory tests may be performed to help check your general health and to find clues to the cause of the diarrhea, such as:

  • Complete Blood Count (CBC)—may be used to check for anemia or to help detect an infection. For example, a type of white blood cell called an eosinophil may be elevated with parasitic infections.
  • Electrolytes—may be done if you are dehydrated, to check for an electrolyte imbalance
  • Osmolality—blood, urine, or stool samples may be tested 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 and biopsy parts of the digestive tract. Visit the National Institute of Diabetes and Digestive and Kidney Diseases web pages on:


The best ways to prevent an infection of your digestive tract 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 your household has a diarrheal infection, all family members should practice careful hand washing. It is best to have the infected person avoid preparing food or drink for others until their infection is over.

When traveling to emerging nations, it is best to drink only bottled water, carbonated drinks, and hot cooked foods. Avoid fresh fruits and vegetables, limited to those that can be easily peeled. 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 your infection is due to contaminated food served at a restaurant or due to a contaminated community water supply, then public health officials will take steps to prevent the spread of the infection.


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 are used to identify the cause of your diarrhea and then the treatment will be tailored to the cause.

For infections caused by viruses and many pathogenic bacteria, the main treatment is to address dehydration to make sure that you drink plenty of liquids to replace 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 digestive tract resolve without specific treatment 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.

You should talk to your healthcare provider before taking any 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, you may need to eliminate the food from your diet. A diagnosis of celiac disease may require that you avoid of all foods containing gluten (gluten-free diet).

For Health Professionals - Optimal Testing: Stool Reducing Sugars

**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.


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