Last Review Date: January 2, 2018

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 will be blood and/or mucus in the stool. Most adults experience several brief bouts of uncomplicated diarrhoea each year that are usually short 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. Diarrhoea can lead to dehydration and electrolyte imbalance, and may need hospitalisation. In infants, significant dehydration can occur much more quickly than adults - within a couple of days.

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 who have HIV/AIDS, cancer, or organ transplants).

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 (so called food poisoning).

Those who visit developing countries are often at risk of exposure to viral, bacterial and parasitic infections (see also Traveller's Diseases). Something as simple as contaminated ice cubes, a fresh fruit salad or food from a market can cause illness. Once a person is infected, they may then 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 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.

Common causes of acute diarrhoea

Parasites: The most common parasites in Australia 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, a much wider range of parasites is 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 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: noroviruses, adenoviruses, calciviruses, cytomegalovirus (CMV) and HIV. In the last couple of years norovirus has frequently been mentioned in the news for causing outbreaks of gastroenteritis on cruise ships. They also cause illness in nursing homes, schools, military establishments and anywhere that people congregate.


  • Salmonella, often found in raw eggs and poultry and may be carried by reptiles kept as pets.
  • Shigella, from faecally contaminated food and water
  • Campylobacter, from raw or undercooked poultry
  • Escherichia coli 0157:H7 (E. coli), associated with raw or undercooked hamburger/ beef. It causes bloody diarrhoea and may lead to haemolytic uraemic syndrome (red blood cell destruction and kidney failure)
  • Clostridium difficile, related to previous antibiotic treatment
  • Others: Staphylococcus aureus and species of Yersinia and Vibrio.

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 – the ‘good’ bacteria that inhabit the gastrointestinal tract, help digest our food, and provide a protective barrier against the ‘bad’ bacteria (pathogen). When the growth of the normal flora is inhibited, it allows easier access for a pathogen to grow and multiply. A toxin produced by the bacterium Clostridium difficile is often the culprit in antibiotic related 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:

  • Inflammatory bowel conditions such as Crohn’s disease
  • Bowel disease such as may be seen in irritable bowel syndrome
  • Malabsorption diseases such as cystic fibrosis
  • Stomach or gallbladder surgery (the rate at which the food travels through the digestive tract may change)
  • Food intolerance such as lactose intolerance or coeliac disease
  • Chemotherapy or abdominal or gastrointestinal radiation
  • Endocrine diseases such as diabetes and thyroid disease
  • Self-induced with laxatives
  • Psychological causes such as stress


Your doctor will want to ask you about your diarrhoea. The frequency, quantity and consistency of bowel movements are very individual. They depend on your metabolism, the foods you eat, your activity level, the amount of fluids you drink, the medications 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, and for alterations that he or she knows 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 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 Australia recently?
  • Are any of your family members, close acquaintances or co-workers ill?
  • Have you been on antibiotics lately?

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. However, if your diarrhoea is severe, if there is blood or mucus present or if it is continuing unabated he or she may request one or more of the following tests. This is especially true if you have been abroad or have eaten or drunk anything that has also made someone close to you ill. Testing may include:

  • Ova and parasite examination. A microscopic examination of your stool for parasites and the ova (eggs, cysts) of parasites.
  • 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.
  • Antigen tests for giardia, cryptosporidium and E. histolytica are available but not routinely used in Australia. 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.
  • Food allergy and intolerance tests (such as tests for lactose intolerance).
  • Coeliac disease tests, such as anti-TTG and anti-endomysial antibodies.
  • 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. 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 intestines (rarely done) to look for signs of parasitic infection

Non-laboratory tests
Sometimes upper gastrointestinal endoscopy, sigmoidoscopy or colonoscopy are used to look at portions of the gastrointestinal tract.


The best way to prevent a bacterial, parasitic or viral gastrointestinal infection is not to 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.

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 stalls is generally not considered safe.

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.

In Australia 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.


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. Most bacterial infections of the GI tract resolve by themselves in healthy people. In some cases, antibiotics actually prolong the infection and may lead to carrying the organisms for months ("carrier state").

Patients with underlying diseases, such as cancer or HIV, may be treated with antibiotics since they cannot clear the infection on their own. If it is severe, stools are bloody or include 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 have eaten food or consumed liquids that may have been contaminated.

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 themselves 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 and organ transplants) 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.

Related pages

On this site

Tests: Clostridium difficile, Ova & Parasites
Conditions: Coeliac disease, cystic fibrosis, Inflammatory Bowel Diseases, Traveller's Diseases 

Elsewhere on the web
Better Health Channel: Diarrhoea
Healthdirect Australia: Diarrhoea
RCPA Manual: Diarrhoea
Traveller's diarrhoea (Better Health Channel)