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Gastric flu

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Gastroenteritis is an infection of the stomach and bowel. The most common symptoms are repeated episodes of diarrhoea (three or more episodes within the space of 24 hours) and vomiting.

These pages focus on gastroenteritis in adults. For information on childhood (rotavirus) gastroenteritis, see the Health A-Z topic on Gastroenteritis in children

How common is gastroenteritis?

Gastroenteritis is very common: approximately 1 in 5 people are affected by the condition in England every year.

Gastroenteritis can be caused by a virus such as the norovirus, or by a number of different types of bacteria. Typically, bacterial gastroenteritis develops as a result of food poisoning.

How gastroenteritis is spread

Most forms of gastroenteritis are highly infectious. The condition is mainly spread through what is known as the faecal/oral route - when bacteria found in faeces (stools) are transferred to your mouth.

Bacteria can be transferred this way through poor hygiene. For example, if someone does not wash their hands after going to the toilet, any viruses or bacteria on their hands will be transferred to whatever they touch, such as a glass, kitchen utensil or food. If you touch this contaminated object then touch your face, or if you eat contaminated food, you may swallow some of the viruses or bacteria. This causes the symptoms of gastroenteritis.

If you have gastroenteritis, do not return to work until 48 hours after passing a normal (solid) stool.


Most people with gastroenteritis have only mild symptoms, and the condition improves within a few days without the need for treatment.

However, if symptoms are severe, or the person is vulnerable because of their age or because of another illness, hospital treatment may be required. This is because diarrhoea can make a person become quickly dehydrated, which can be fatal in severe cases.

There are an average of 190 deaths caused by gastroenteritis each year in England and Wales. Most of these deaths occur in people aged over 65.


Antibiotics are medicines that can be used to treat infections caused by micro-organisms, usually bacteria or fungi. For example amoxicillin, streptomycin and erythromycin.


Bacteria are tiny, single-celled organisms that live in the body. Some can cause illness and disease and some others are good for you.


Diarrhoea is the passing of frequent watery stools when you go to the toilet.


The sac-like organ of the digestive system. It helps digest food by churning it and mixing it with acids to break it down into smaller pieces.

Symptoms of gastroenteritis

In cases of viral gastroenteritis, symptoms usually begin within 24-48 hours after becoming infected (this time period is known as the incubation period).

The incubation period for bacterial gastroenteritis can range from 12 hours to five days, depending on the bacterium responsible.

The most common symptom of gastroenteritis is repeated episodes of diarrhoea. Usually, loose and watery stools are passed three or more times within 24 hours. The stools may contain traces of blood and mucus.

Other symptoms of gastroenteritis include:

  • vomiting
  • nausea
  • stomach cramps
  • headaches
  • moderately high temperature (fever) of 38-39ºC (100.4-102.2ºF)


Be alert for symptoms suggesting that you or someone in your care are becoming dehydrated (where the water content of the body is particularly low).

Dehydration can cause serious and potentially fatal complications. Elderly people are particularly vulnerable to the effects of dehydration.

Symptoms of dehydration include:

  • tiredness
  • apathy (a lack of emotion or enthusiasm)
  • dizziness
  • nausea
  • headaches
  • muscle cramps
  • dry mouth
  • pinched face
  • sunken eyes
  • passing little or no urine
  • rapid heartbeat

See treating dehydration for advice on how to counter the effects of dehydration.

When to seek medical advice

Most cases of gastroenteritis do not need medical treatment as the symptoms will pass within a few days - typically two to three days for viral gastroenteritis and four to seven days for bacterial gastroenteritis.

There may be circumstances where medical treatment is required. Contact your GP if you have any of the following:

  • vomiting that lasts more than two days
  • you cannot keep liquids down for more than a day
  • diarrhoea that lasts more than three days
  • blood in your vomit
  • blood in your stools
  • seizures (fits)
  • changes in mental state, such as confusion
  • double vision
  • slurred speech
  • signs of dehydration, such as a dry mouth, sunken eyes and being unable to pass urine
  • your symptoms do not begin to improve after three days
  • you suspect that you caught gastroenteritis while travelling in the developing world; particularly if you were visiting a part of the world with a poor standard of water hygiene

Parts of the world known to have poor levels of water hygiene include:

  • sub-Saharan Africa (all the countries south of the Sahara Desert)
  • countries in South Asia, such as India, Bangladesh and Pakistan
  • Central and South America

Also contact your GP if you have pre-existing risk factors that make you vulnerable to developing a serious complication from infections, such as:


Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.
Dehydration is an excessive loss of fluids and minerals from the body.
Diarrhoea is the passing of frequent watery stools when you go to the toilet.
Stool (also known as faeces) is the solid waste matter that is passed from the body as a bowel movement.
A high temperature, also known as a fever, is when someone's body temperature goes above the normal 37°C (98.6°F).
Loss of appetite
Loss of appetite is when you do not feel hungry or want to eat.
Pain is an unpleasant physical or emotional feeling that your body produces as a warning sign that it has been damaged.
Vomiting is when you bring up the contents of your stomach through your mouth.

Causes of gastroenteritis

Gastroenteritis is an infection of the stomach and intestines (bowel). The infection interferes with one of the main functions of the intestines, which is the absorption of water from the contents of your intestines and into the body.

This is the reason why the most common symptom of gastroenteritis is watery diarrhoea, and why dehydration is such a common complication.

The most two most common causes of gastroenteritis in adults in England are:

  • a norovirus infection
  • food poisoning caused by bacteria


Noroviruses are the most common cause of viral gastroenteritis in adults. Norovirus infections are sometimes called 'winter vomiting disease' because people tend to get them during the winter months. However, norovirus infections can occur at any time of the year.

Norovirus outbreaks are common, particularly within contained environments such as hospitals, nursing homes, schools and cruise ships. This is because the illness spreads very easily from person to person, and the virus can survive for several days in a contaminated area.

Noroviruses can be spread through contact with an infected person, through contact with contaminated surfaces or objects, or by eating or drinking contaminated food or water.

There are many different types of norovirus, and it is possible for a norovirus infection to occur several times. This is because after getting the illness, immunity to the virus only lasts for 14 weeks.

For more information, take a look at the Health A-Z topic on norovirus infections.

Food poisoning

Most cases of bacterial gastroenteritis are caused by food poisoning.

Some cases of viral gastroenteritis are also caused by food poisoning. Food can be contaminated with a virus if handled by a person with a viral infection.

Food can become contaminated at any stage during its production, processing or cooking. For example, it can be caused by:

  • not cooking food at the right temperature and/or for the right length of time
  • not chilling food at the correct temperature
  • the food being handled by someone who has not washed their hands properly
  • people eating food after it has passed its 'use by' date
  • cross-contamination

For more information, see the Health A-Z topic on food poisoning.


Cross-contamination is a cause of food poisoning that is often overlooked. It occurs when harmful bacteria are spread between food, surfaces and equipment.

For example, if you prepare raw chicken on a chopping board and then do not wash the board before preparing a ready-to-eat meal such as a salad or sandwiches, harmful bacteria can be spread from the chopping board to the ready-to-eat meal.

Cross-contamination can also occur if you store raw meat above ready-to-eat meals. The meat juices can drip onto the meals and contaminate them.

The most common types of bacteria associated with gastroenteritis are:

  • campylobacter - a bacterium found in raw meat and poultry, unpasteurised milk and untreated water
  • salmonella - a bacterium found in raw meat, poultry, eggs and unpasteurised milk
  • escherichia coli (E. coli) - a bacterium found in undercooked beef and unpasteurised milk

Travellers' diarrhoea

Travellers' diarrhoea is a term used to refer to gastroenteritis that is acquired when travelling abroad. Travellers' diarrhoea can be caused by a range of different bacteria or parasites such as:

  • the shigella bacterium or the entamoeba parasite, which are both spread through poor hygiene and cause a type of travellers' diarrhoea known as dysentery
  • cryptosporidium, which is a parasite found in soil, food or water that has been contaminated with animal or human faeces
  • giardia intestinalis, which is a parasite found in water that has been contaminated with animal or human faeces (infections caused by this parasite are known as giardiasis)

For more information about these, see the Health A-Z topic on travellers' diarrhoea.

Diagnosing gastroenteritis

In most cases of gastroenteritis, you will not need a diagnosis from your GP because your symptoms should get better without any treatment.

If your symptoms persist or are severe, your GP may take a sample of your stools (faeces). This can be checked for the presence of specific bacteria or parasites. If a bacterium or parasite is identified, your GP can prescribe the most suitable antibiotic or anti-parasitic medication for your condition.

In some circumstances, blood and urine tests may be used to rule out other conditions, such as a urinary tract infection or pneumonia. This is normally recommended when your symptoms suggest that the infection is not limited to your digestive system. Such symptoms include:

  • high temperature (fever) of 38ºC (100.4ºF) or above
  • rapid heartbeat
  • low blood pressure (hypotension)

Treating gastroenteritis

Most cases of gastroenteritis will get better within a few days without treatment. More severe cases may need treatment with medication. Self-care advice and information on medication is outlined below.

Caring for yourself at home

It is very important to replace any fluids that your body loses through diarrhoea and vomiting. Aim to drink at least 2 litres (3.5 pints) of water a day, as well as 200ml (a third of a pint) of water every time you pass diarrhoea.

If you are more vulnerable to the effects of dehydration - for example, if you are elderly or you have another pre-existing condition - then rehydration salts are recommended.

Rehydration salts are available in sachets from pharmacies. You dissolve them in water and they help to replace salt, glucose and other important minerals that your body loses via dehydration.

Some types of rehydration salts may not be suitable if you have a kidney condition. Your pharmacist or GP can give you advice on this.

Try to maintain a normal, healthy diet. Avoid foods that are high in fat and sugar because these could make your symptoms worse. You should be able to tolerate light plain foods (e.g. rice or wholemeal bread) more than spicy or rich foods.

You may find that eating six light meals a day is easier to tolerate than three large meals.


Medication is not usually required for the treatment for gastroenteritis unless your symptoms are particularly severe. Medications used to treat the symptoms of gastroenteritis are described below.

Antidiarrhoeal medications

Antidiarrhoeal medications are used to treat the symptoms of diarrhoea. A widely used antidiarrhoeal medication for the treatment of gastroenteritis is loperamide.

Loperamide slows down the movement of your bowel contents and sometimes increases water absorption from the gut.

Common side effects of loperamide include:

  • constipation
  • dizziness

Rarer side effects of loperamide include:

  • cramps
  • drowsiness
  • skin rashes
  • bloating

Loperamide is not suitable for people with colitis (inflammation of the colon) or pregnant women, although it can be used safely by breastfeeding women.

Do not take loperamide (or any other antidiarrhoeal medication) if you have a high temperature (fever) of or above 38ºC (100.4ºF), or if you have blood and/or mucus in your stools. This is because the medication could make your symptoms worse.

Do not give antidiarrhoeal medication to children under 12 unless directly instructed to by your GP.


Anti-emetic medications are used to help prevent or reduce vomiting. They are usually only required if your vomiting is severe and places you at risk of dehydration.

A type of anti-emetic known as metoclopramide can be used for this purpose. Metoclopramide is given by injection directly into your muscles.

Metoclopramide helps to relax the muscles used during vomiting while at the same time speeding up the absorption of fluids and foods by the digestive system.

The most common side effects of metoclopramide are:

  • drowsiness
  • restlessness
  • fatigue
  • anxiety
  • insomnia
  • depression

These side effects are usually temporary and should pass once you finish taking the medication.


Antibiotics are not normally recommended for the treatment of gastroenteritis. This is because:

  • most cases of gastroenteritis are caused by viruses
  • even if gastroenteritis is caused by bacteria, research shows that antibiotics are often no more effective than waiting for the symptoms to pass, and they can cause unpleasant side effects
  • every time you use antibiotics to treat a mild condition, it is more likely that their effectiveness for treating more serious conditions is reduced

However, if your gastroenteritis is particularly severe and a specific bacterial cause has been identified, antibiotics may be recommended.

Antibiotics may also be recommended if you have a pre-existing risk factor that makes you more vulnerable to infection, such as having a weakened immune system.

Side effects of using antibiotics to treat gastroenteritis include:

  • nausea
  • vomiting
  • diarrhoea
  • stomach pain
  • skin rashes

Hospital treatment

Hospital treatment may be required for people with serious dehydration caused by gastroenteritis.

Admission to hospital is usually recommended when:

  • repeated episodes of vomiting make you unable to keep down any fluids
  • you have symptoms suggesting that you have severe dehydration, such as not passing any urine

Hospital treatment involves administering fluids and nutrients intravenously (directly into the vein).


Antibiotics are medicines that can be used to treat infections caused by micro-organisms, usually bacteria or fungi. For example amoxicillin, streptomycin and erythromycin.
Bacteria are tiny, single-celled organisms that live in the body. Some can cause illness and disease and some others are good for you.
Dehydration is an excessive loss of fluids and minerals from the body.
Diarrhoea is the passing of frequent watery stools when you go to the toilet.
The sac-like organ of the digestive system. It helps digest food by churning it and mixing it with acids to break it down into smaller pieces.
Intravenous (IV) means the injection of blood, drugs or fluids into the bloodstream through a vein.
Vomiting is when you bring up the contents of your stomach through your mouth.

Preventing gastroenteritis

Infection control

As gastroenteritis can be very infectious, it is important to take steps to prevent it from spreading to other people. These include:

  • washing your hands thoroughly after going to the toilet and before eating or preparing food
  • cleaning the toilet, including the handle and the seat, with disinfectant after each bout of diarrhoea and/or vomiting
  • not sharing towels, flannels, cutlery or utensils with other household members
  • not returning to work until 48 hours have passed since your last bout of diarrhoea and/or vomiting

Food hygiene

Practising good food hygiene will help you to avoid developing gastroenteritis as a result of food poisoning. Some ways of achieving this are:

  • regularly washing your hands, surfaces and utensils with hot, soapy water
  • never storing raw and cooked foods together
  • making sure that food is kept properly refrigerated
  • always cooking your food thoroughly
  • never eating food that is past its sell-by date

For more information, see preventing food poisoning.

Preventing travellers' diarrhoea

If you are travelling in a country where the standards of public hygiene are low and there is a risk of water contamination, such as in some African or Asian countries, avoid the following food and drink:

  • tap water
  • fruit juices (if sold by a street vendor)
  • ice cream or ice cubes
  • shellfish
  • eggs
  • salads
  • raw or undercooked meat
  • peeled fruit
  • mayonnaise
  • sauces

Food and drink that are generally safe to eat include:

  • sealed bottled water that is produced by a recognised international manufacturer
  • cooked food, such as soup or stir-fry
  • canned food or food in sealed packs
  • fresh bread
  • unpeeled fruit
  • tea or coffee
  • alcohol

Also make sure that you have the recommended vaccinations for the country you are visiting.

For more information see preventing travellers' diarrhoea and the Health A-Z topic on travel vaccinations.


In children and the elderly, there is an increased risk of dehydration and shock resulting from gastroenteritis.

Other complications can include damage to the mucosa (sticky lining) of the intestines, causing prolonged watery diarrhoea even after the initial infection has gone.

Some people experience a temporary lactose intolerance (reacting badly to dairy foods ) because of increased sensitivity of the lining of the intestines. This can also lead to the development of irritable bowel syndrome.


Shock is a short-term state of body weakness that usually happens after an accident of injury, caused when there is an insufficient supply of oxygen t
Diarrhoea is the passing of frequent watery stools when you go to the toilet.
Dehydration is an excessive loss of fluids and minerals from the body.

The materials in this website are provided by Medicine Chest and NHS Choices.  Neither Co-operative Group Limited or Co-operative Healthcare Limited (trading as The Co-operative Pharmacy or otherwise) shall be in any way responsible or liable for its content.

The materials in this website are in no way intended to replace the professional medical care, advice, diagnosis or treatment of a doctor.  The website does not have answers to all problems and answers to specific problems may not apply to everyone.  If you notice medical symptoms or feel unwell, you should consult your doctor.  For further information, consult the terms and conditions.

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