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Gastroenteritis is an inflammation of the stomach and intestines caused by infection. In most cases, gastroenteritis clears up without the need for specific medical treatment.

The stomach and intestines are known collectively as the gastrointestinal tract - or gut. Gastroenteritis is an infection of the gut. You can get infected from eating or drinking food that is contaminated with bacteria, viruses or parasites, or from other infected people (for more information, see Causes).

Some of these germs can damage the cells lining the inner surface of the gut and interfere with its normal functions.
Certain bacteria or viruses may also produce toxins that irritate the gut and cause it to produce excess amounts of fluid. This can lead to the various symptoms of gastroenteritis such as diarrhoea.

The time between catching the infection and the start of symptoms - the incubation period - depends on the cause of gastroenteritis. Depending on the type of infection, it can range from a few hours to a couple of weeks.

You may have some or all of the following symptoms:

  • diarrhoea, which may contain blood and mucus, or be watery, greasy or frothy
  • nausea and vomiting
  • abdominal cramping, bloating or pain
  • fever

Most people recover within a week. However, with severe infections, which are uncommon in Hong Kong, the illness may persist for many weeks. It is important to see your GP if your symptoms last for more than a week, or if you have recently travelled abroad.

The symptoms of gastroenteritis may be confused with other conditions, such as irritable bowel syndrome (IBS), Crohns disease or ulcerative colitis .

Complications from gastroenteritis occur mainly in the young and the old, in people with chronic gastroenteritis and in those who have weakened immune systems.

Possible complications of gastroenteritis include:

  • dehydration - this can lead to kidney failure if severe
  • malnutrition
  • irritable bowel syndrome

You should contact your GP if:

  • your pain is severe or does not respond to normal painkillers
  • your vomiting or diarrhoea continues for more than a few days or you cant hold fluids down - this can lead to dehydration
  • there is blood or mucus in the diarrhoea
  • you have signs of moderate or severe dehydration, including a very dry mouth, muscle cramps, reduced urine, sunken eyes and, later, confusion or irritability
  • you have recently travelled abroad
  • you can´t keep down medicines you normally take


Viruses are a major cause of gastroenteritis. These include:

  • rotavirus
  • norovirus
  • enteric adenovirus
  • hepatitis A

Viral infection can be seasonal and there is a peak of infections with rotaviruses and noroviruses during the winter months.


The most common cause of bacterial gastroenteritis is food poisoning. Food poisoning is caused by different bacteria from different foods, for example:

  • Salmonella - dairy, eggs and poultry
  • Campylobacter - dairy, meats and poultry
  • Bacillus - reheated rice
  • Vibrio - seafood
  • Escherichia coli (E. coli) - minced beef

Some E. coli strains are particularly harmful, including E. coli 0157, which produces a toxin that can also damage the kidneys, cause red blood cells to break down and cause inflammation in small blood vessels. These infections can be fatal and children can be particularly vulnerable.


Parasites rarely cause gastroenteritis in Hong Kong, but are a major problem in less developed countries and can be caught if you go abroad.

Other causes

Some food allergies, for example an allergy to strawberries, can lead to gastroenteritis.

Diarrhoea can also be caused by other infections such as pneumonia or urinary tract infections. However, very occasionally it may be caused by other conditions such as encephalitis, diabetes, appendicitis or a blockage of the gut.

Some medicines, such as antimalarials, can also cause symptoms of gastroenteritis. Antibiotics can lead to gastroenteritis by killing the normal, healthy bacteria in your gut.

The infections are transmitted:

  • in contaminated food
  • from person to person - this happens if an infected person goes to the toilet and doesn't wash their hands properly afterwards, before handling food or touching other people
  • if an individual infected with a virus sneezes or coughs, as another person could inhale a virus
  • in shellfish harvested in polluted waters
  • in contaminated drinking water - the majority of infections are carried this way in the developing world but can also affect travellers

Your GP will ask you about your symptoms and examine you. He or she may also ask about your medical history. He or she may also ask you for a faeces (stool) sample to send for laboratory testing.

If you have been travelling, your GP will ask you which countries you have visited and which vaccinations you have had.


Most cases of gastroenteritis can be treated at home.

The most important aspect of treatment is to replace the fluids and salts you have lost, to prevent dehydration.

  • If you have a mild case of gastroenteritis, your usual daily drinks (water, squash) should be enough. You can continue to eat normally, but you shouldn't have fatty foods or food or drinks that have lots of sugar.
  • If you have a more severe infection, use an oral re-hydration solution (eg Dioralyte), which you can buy in pharmacies. These are usually a powder that is made up into a solution by adding water. They contain the right balance of sugars and salts for your body and they encourage re-hydration. You should eat foods high in carbohydrates such as rice or toast until you can take solid food and return to a normal diet.

Probiotics (foods containing live, beneficial bacteria) can help to reduce the duration of diarrhoea.


Medicines to stop diarrhoea such as loperamide (eg Imodium) are only recommended for adults. These medications slow down movement in the intestines, but have no effect on the excess fluid in the intestines, so it will come out later. They can also cause side-effects such as tummy cramps, dizziness and skin reactions.

If you are in pain, take the painkiller that you would normally take for a headache. Follow the instructions in the patient information leaflet that comes with the medicine and ask your pharmacist for advice.

Your GP may prescribe an anti sickness medicine (anti-emetic). Vomiting normally stops when you have drunk enough fluid, but anti-emetics can be helpful if you have severe vomiting. Many anti-emetics are also sedatives, so it is advisable not to drive or use machinery after taking them.

Most cases of gastroenteritis are caused by viruses, which are not treatable with antibiotics. Your GP wont usually prescribe antibiotics for gastroenteritis.

However, if your GP suspects that you have a bacterial infection, he or she may ask you for a stool sample to send for laboratory testing. This is more common if you have been travelling recently. The results will help to determine which antibiotic to treat you with.

Hospital treatment

If you have lost so much fluid that you are very dehydrated, hospital treatment may be needed to replace fluids directly into your bloodstream (intravenously).

The best way to prevent gastroenteritis is to always wash your hands with soap after going to the toilet and to disinfect toilets after use.
You should also practise good food hygiene.

Before travelling make sure you have had any vaccinations required and use bottled water if necessary when abroad.

If you have gastroenteritis, help to prevent spreading the infection to other family members by:

  • hygienically disposing of, or properly cleaning, all soiled items such as towels
  • cleaning the toilet with disinfectant
  • not sharing towels and flannels
  • not preparing food for others

If you have gastroenteritis you may be infectious to others. You should stay away from work, school or college for at least 48 hours after your symptoms have stopped.

1. What are probiotics and how can they help if I have gastroenteritis?

Probiotics are a food supplement. They contain live bacteria and yeasts that can be helpful in restoring the balance of bacteria in your gut after a bout of gastroenteritis.

Probiotics are food supplements containing live bacteria and yeasts that help restore the balance of bacteria in your gut. Bacteria are often thought of as harmful and causing ill-health, but there are many good bacteria that live in and on your body that help keep you healthy. This is especially so in your gut. Good bacteria in your gastrointestinal tract prevent harmful organisms from growing in your bowel or entering your body through your intestine.

Gastroenteritis is an infection in your gut caused by harmful bacteria, viruses or parasites. These germs damage the cells lining the inner surface of your gut interfering with its normal processes and upsetting the balance of bacteria. Taking probiotics which contain bacteria such as lactobacillus helps to restore the balance of good bacteria in your gut. This can relieve symptoms of diarrhoea and speed up your recovery.

You can buy probiotics as food supplements (capsules or tablets) from your pharmacist or health food shop. Always read the patient information leaflet that comes with your supplements. Or, they can be bought as yogurts or drinks (eg Danone Activa or Actimel) from your supermarket. Plain yogurts don't contain probiotics.

If you have any questions or concerns about probiotics or gastroenteritis, talk to your GP.

2. Why are people who take antibiotics more prone to getting gastroenteritis?

Some antibiotics can upset the balance of good bacteria in your gut allowing harmful bacteria to thrive. This is often referred to as antibiotic-associated diarrhoea and can cause painful stomach cramps and watery diarrhoea.

Antibiotics are medicines prescribed by doctors to treat infections (for example, a kidney infection). They are used to kill or prevent the growth of harmful bacteria in your body. However, some antibiotics, such as ampicillin, clindamycin, and cephalosporins, will also kill the normal bacteria in your gut. This can allow other bacteria such as Clostridium difficile (C. difficile), to grow and thrive in your gastrointestinal tract. As this bacterium multiplies and divides, it produces a toxin which causes pain in your abdomen and watery diarrhoea - gastroenteritis. This is also known as antibiotic-associated diarrhoea.

It's not clear how many people get diarrhoea as a result of taking antibiotics. It has been estimated that it could be as many as one in four people, although the actual number may be much lower.

Most people who get antibiotic-associated diarrhoea experience only mild symptoms that usually resolve themselves quite quickly. It's important to seek advice from your GP if you have symptoms rather than stopping the course of antibiotics yourself. If possible, he or she will take you off the antibiotic and prescribe a different type.

While you have symptoms, you should continue with your normal diet, but leave out fatty foods or food and drink with a high sugar content, and make sure you drink enough fluids. You may find that you become intolerant to milk for a couple of weeks after your bout of gastroenteritis. This is because you are temporarily unable to break down the lactose (milk sugar) in it, giving you diarrhoea. Milk and milk products are best avoided if they make your diarrhoea worse. If you have become dehydrated, you can take oral rehydration salts (eg Dioralyte). Taking probiotic supplements or yogurt drinks can also be helpful in easing symptoms of diarrohea.

Very occasionally, a C. difficile infection in your gut can develop into a serious disease and symptoms can be severe. If your diarrhoea doesn't improve and you are in a lot of discomfort, you should see your GP as soon as you can. He or she will take a stool sample and blood test for analysis before referring you on for further treatment.

If you have any questions or concerns about antibiotics or gastroenteritis, talk to your GP.

3. How should I prepare food to avoid getting gastroenteritis or giving it to others?

Every year millions of people suffer from gastroenteritis caused by poorly prepared or stored food. Following food hygiene measures can ensure that you and the people you cook for don't become ill.

To prevent gastroenteritis it's important to take care over how you prepare, cook and store food. The following food hygiene tips will help you to keep yourself and those you cook for safe.

Preparing food

When preparing food it's important to make sure that bacteria aren't spread through cross-contamination, for example, raw food placed in contact with food that is ready to eat, cooking utensils, chopping boards or people's hands. To prevent this:

  • wash your hands before you start preparing food and after touching raw food (especially meat)
  • prepare raw foods and foods that are ready to eat separately
  • clean knives and chopping boards thoroughly after you have used them to prepare raw meat
  • keep cloths, tea towels and hand towels clean and change them regularly
  • \

Cooking food

During cooking any harmful bacteria in your food are destroyed, so it's important to make sure you cook everything properly. Do this by:

  • allowing meat and poultry to thaw thoroughly before cooking
  • making sure your food is hot all the way through before you eat it
  • never reheating food more than once

Storing food

Some foods need to be kept chilled in the fridge to keep them safe. When storing these types of food always:

  • put them in the fridge straight away
  • cool cooked foods as quickly as possible before putting them in the fridge
  • use separate, sealed containers to store raw meat and poultry in your fridge
  • don't overfill your fridge, otherwise the cold air won't be able to flow properly and food may become too warm

When preparing food for the elderly, babies and toddlers, pregnant women or people who are ill, don't give them food that contains any raw or runny eggs (ie mayonnaise). Raw eggs can contain bacteria which may be harmful to those people.

Food hygiene standards are not always as high abroad as they are at home. Also, you may encounter bacteria that you have not been exposed to before. To reduce the risks while on holiday try to do the following.

  • Ensure you have any suggested vaccinations well before leaving, in particular typhoid and cholera. Your GP will have an up-to-date list of these for the area you are visiting.
  • Only drink bottled water and ensure the seal has not been broken when you buy it. You should also use this for brushing your teeth. Avoid ice in drinks if you don't know where the water came from.
  • Peel fruit and avoid salad leaves unless you have washed them yourself in bottled or sterilised water.
  • Be cautious with shellfish and eggs (especially raw eggs in foods like mayonnaise) which are the commonest source of salmonella abroad.
  • If you have any questions or concerns about gastroenteritis and food hygiene, talk to your GP.

Further information



  • Gastroenteritis. Clinical Knowledge Summaries., accessed 10 March 2010
  • Gastrointestinal disease. Health Protection Agency (HPA)., accessed 10 March 2010
  • Diarrhoea and vomiting in children under 5. National Institute for Health and Clinical Excellence (NICE), 2009, CG84.
  • Allen SJ, Okoko B, Martinez EG et al. Probiotics for treating infectious diarrhoea. Cochrane Database of Systematic Reviews 2003, Issue 4
  • Antimotility drugs. British National Formulary., accessed 12 March 2010
  • Understanding NICE guidance: Diarrhoea and vomiting in children. National Institute for Health and Clinical Excellence (NICE), 2009, cg84.
  • Ejemot RI, Ehiri JE, Meremikwu MM, et al. Hand washing for preventing diarrhoea. Cochrane Database of Systematic Reviews 2008, Issue 1
  • Probiotics. The British Dietetic Association., accessed 14 March 2010
  • Diarrhoea: Can probiotics help? Informed Health Online., accessed 14 March 2010
  • Simon C, Everitt H, van Dorp F. Oxford handbook of general practice. 3rd ed. Oxford: Oxford University Press, 2010:427
  • Diarrhoea - antibiotic associated. Clinical Knowledge Summaries., accessed 14 March 2010
  • Preparing. Food Standards Agency., accessed 14 March 2010
  • Cleaning. Food Standards Agency., accessed 14 March 2010
  • Cooking. Food Standards Agency., accessed 14 March 2010
  • Storing and preparing. Food Standards Agency., accessed 14 March 2010
  • Pediatrics, gastroenteritis. emedicine., accessed 14 March 2010
  • Dehydration. emedicine., accessed 14 March 2010

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