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This article waslast modified on 7 February 2022.
What is it?

Diarrhoea is a common symptom of an ‘upset tummy’ – a gastrointestinal disturbance. It produces frequent watery stools and may be accompanied by abdominal pain, feeling sick, and tiredness. Sometimes there is blood and/or mucus in the stool. Most adults experience several brief bouts of uncomplicated diarrhoea each year that are usually short-lived and self-limiting, resolving themselves within a few days and cause nothing more than temporary discomfort. However, severe diarrhoea or diarrhoea which lasts several weeks can be dangerous, especially to very young children and the elderly. When diarrhoea is severe or lasts a long time it can lead to dehydration and electrolyte imbalance, and some of those affected may need to be admitted to hospital. In infants, significant dehydration can occur much more quickly than adults, sometimes within a day or two.


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About Diarrhoea
  • Common causes

    There are many infectious and non-infectious causes of acute and chronic diarrhoea. Viral, bacterial, and parasitic infections can cause diarrhoea that lasts several days to a few weeks, although some cases may linger causing chronic diarrhoea in those with suppressed immune systems (such as those with HIV/AIDS, cancer or organ transplantation). These sorts of diarrhoea are infectious, with the virus, bacteria, or parasite being 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.

    Once a person is infected, they may then pass the infection on to others around them unless careful hygiene practices (especially thorough hand washing) are followed. This route for the spread of infection presents a challenge in households with infected infants, in day care centres 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 visit developing countries are often at risk of exposure to viral, bacterial, and parasitic infections. Things as simple as contaminated ice cubes, a fresh fruit salad, or food from an open market can cause illness.

    Common causes of acute diarrhoea:

    Parasites: The most common parasites in the UK are Giardia lamblia (giardia), Entamoeba histolytica (E. histolytica) and Cryptosporidium parvum. These single cell parasites are found in mountain streams and lakes throughout the world and may infect swimming pools and occasionally public 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 countries and in warm climates, a much wider range of parasites may be 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’ ova but some of the parasites can also penetrate the skin.

    Viruses: Rotavirus is the most common cause of severe diarrhoea among children. Other viruses include: Norwalk, noroviruses (also called Norwalk-like viruses), adenoviruses, calciviruses, cytomegalovirus (CMV), and HIV. In the last couple of years Norwalk and Norwalk-like viruses have frequently been mentioned in the news for causing outbreaks of gastroenteritis on cruise ships. They may cause illness in nursing homes, schools, military establishments and anywhere that people congregate.

    Bacteria: Bacteria can cause diarrhoea by three different mechanisms: infection, production of a toxin in infected food or production of a toxin in the body after infection.

    Bacteria that can infect the gastrointestinal tract include:

    • Salmonella, often found in raw eggs and poultry and may be carried by reptiles kept as pets
    • Campylobacter, from raw or undercooked poultry.
    • Species of Yersinia and Vibrio

    Bacteria that produce a toxin in infected food that can persist after cooking include:

    • Staphylococcus aureus 
    • Bacillus cereus

    Bacteria from food that produce a toxin after multiplying in the gastrointestinal tract include:

    • Shigella, from faecally contaminated food and water
    • Escherichia coli 0157:H7 (E. coli), commonly associated with raw or undercooked beef, but also with a wide variety of prepared foods. Hamburgers made at home and inadequate hand washing by food preparers have been shown to be particular risk factors. After an incubation period of 1 to 10 days it causes diarrhoea which contains blood in over 70% of cases. This bacterium can to lead to red blood cell destruction and kidney failure (the haemolytic uraemic syndrome).

    Acute diarrhoea may also be due to treatment with broad-spectrum antibiotics, or to other medications that cause diarrhoea as a side effect. Antibiotic treatment can decrease the normal flora which are the “good” bacteria that live in the gastrointestinal tract, help digest our food, and provide a protective barrier against the “bad” bacteria (pathogens). When the growth of the normal flora is inhibited, it is easier for a pathogen to grow and multiply. Toxins produced by the bacterium Clostridium difficile are often the culprit in antibiotic related diarrhoea.

    Common causes of chronic diarrhoea:

    Chronic diarrhoea (diarrhoea that lasts for more than a few weeks), sporadic diarrhoea, and diarrhoea that alternates with constipation are most frequently associated with non-infectious causes. These may include:


  • Tests

    Your doctor will want to ask you about your diarrhoea. The frequency, quantity, and consistency of normal bowel movements are very individual. They depend on your metabolism, the foods you eat, your activity level, the amount of fluids you drink, the medicines you take, and even any stress that you are experiencing. Your doctor will be looking for changes from your normal habits, things that are out of the ordinary. The doctor will look for alterations that are commonly associated with diarrhoea-causing conditions. Your doctor will be asking you a series of questions that help choose which laboratory tests will be the most useful. These questions may include:

    • What is the frequency of your stools?
    • How long you have been experiencing diarrhoea?
    • What are the consistency, colour, 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 travelled outside the UK recently?
    • Are any of your family members, close acquaintances or co-workers ill?
    • Have you been on antibiotics lately?
    • If your diarrhoea is persistent or alternates with constipation, have you had any unexpected weight loss?

    Laboratory Tests
    If your diarrhoea is uncomplicated and goes away within a few days, your doctor may not search for the cause of your gastrointestinal upset. He/she may request one or more of the following tests if your diarrhoea is severe, if there is blood or mucus present or if it is continues for sometime. This is especially true if you have been abroad or have eaten or drunk anything that has also made someone close to you ill.

    Tests to identify diarrhoea caused by infection include:

    • Ova and parasite (OCP) examination. A microscopic examination of your stool for parasites and the ova (eggs, cysts) of parasites.
    • Antigen tests for Giardia, Cryptosporidium and E. histolytica are available but not routinely used in the UK. These tests detect protein structures on the parasites. They are more sensitive and specific for these particular parasites than microscopic examination for them and their ova.
    • Stool white blood cells. These may be present in the stool when there is a bacterial infection.
    • Stool culture to check for pathogenic gastrointestinal bacteria.
    • Antibody tests for parasites. These are not as useful to detect current infections but may be requested to check for past or chronic infections, especially if unusual parasitic infections are suspected.
    • Rotavirus test, a rapid antigen test.
    • Clostridium difficile toxin,a rapid test used to identify a Clostridium difficile infection by detecting the toxin made by the bacteria.
    • Electrolytes including sodium, potassium and urea. If you are dehydrated your doctor may want to do a blood test to determine whether your electrolytes have become imbalanced.
    • Biopsy of the small intestine is rarely done to look for signs of parasitic infection
    Tests for non-infectious causes of diarrhoea include:
    • Coeliac disease tests, such as anti-endomysial and anti-gliadin antibodies.
    • Food allergy and intolerance tests (such as tests for lactose intolerance).
    • Faecal calprotectin to differentiate inflamatory bowel conditions such as Crohn's disease from irritable bowel syndrome (IBS)
    Tests to assess the effects of diarrhoea on your metabolism include

    Non-Laboratory Tests
    Endoscopy, sigmoidoscopy or colonoscopy are used to look at portions of the gastrointestinal tract.


  • Prevention

    The best ways to prevent a bacterial, parasitic, or viral gastrointestinal infection are not to drink water or eat food that may be contaminated and to be careful with hygiene 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 diarrhoeal infection, careful hand washing by all family members is recommended. It is best if the infected person does not prepare food or drink for others until the infection is over.

    When you are travelling in developing countries it is best to drink only bottled water, carbonated drinks, and hot cooked foods. Avoid fresh fruits and vegetables, limiting yourself to those that you can peel yourself. Food from street food stores is generally not considered safe.

    In England and Wales reports by laboratory microbiologists to the Communicable Disease Surveillance Centre and notification of infectious disease from doctors form the foundation of communicable disease surveillance. Other than in travel related cases, public health officials will want to try to determine where your infection came from so that they can address any potential concerns. For instance, if your infection is due to contaminated food served at a restaurant or to a contaminated public water supply, steps will need to be taken to prevent the spread of the infection.


  • Treatment

    If your diarrhoea is uncomplicated and goes away within a few days, your doctor is unlikely to prescribe any treatment for your gastrointestinal (GI) upset. In healthy people, most bacterial infections of the GI tract resolve by themselves. In some cases, antibiotics actually prolong the infection and may lead to carrying the organisms for months (carrier state). Patients with underlying diseases that impair the immune response, such as cancer or HIV, may be treated with antibiotics since they cannot clear the infection on their own. If the diarrhoea is severe, bloody, includes mucus and/or has lasted for more than three or four days, then your doctor will often request tests to identify the cause of your diarrhoea and treat it accordingly. This is especially true if you have been abroad or if family members, close acquaintances or co-workers are also ill.

    For viral infections and many pathogenic bacterial infections, the main treatment is to make sure that the patient replaces lost fluids and electrolytes. Infants and those with severe dehydration may not be able to drink enough to rehydrate themselves and may have to be taken into hospital for a short period of time. Your doctor will monitor your health, give you advice on preventing the spread of the infection, and watch for any complications.

    Most parasitic infections are treated with medicine, although some may resolve on their own. With some bacterial and parasitic infections, your doctor may treat the entire family even if only one member is obviously affected. There is currently no effective treatment for Cryptosporidium. Most people with healthy immune systems will get rid of this infection, but some with poor immune systems (such as those with HIV/AIDS or organ transplantation) may develop a chronic infection.

    Talk to your pharmacist before taking an over-the-counter anti-diarrhoea medicine. They relieve symptoms of acute (severe) diarrhoea and can be useful to reduce discomfort and social disruption. Do not take them if there is blood in your stool or you have a raised temperature. Never give anti-diarrhoea medicines to a child. Diarrhoea is one of the methods your body uses to help get rid of the infection. If you slow down or prevent this from happening by taking an anti-diarrhoea medicine you can prolong the time that you are ill.

    For diarrhoea caused by a food intolerance such as lactose intolerance, treatment involves avoidance of the cause.   A diagnosis of coeliac disease requires avoidance of foods containing gluten.