Gastroenteritis is an infection of the stomach and bowel (large intestine).

The most common symptoms are vomiting and repeated episodes of diarrhoea (three or more episodes within 24 hours).

The causes and treatment of gastroenteritis can differ between children and adults. This section is about gastroenteritis in adults.

What causes gastroenteritis in adults?

The two most common causes of gastroenteritis in adults are the norovirus and food poisoning.

The infection interferes with one of the main functions of the intestines – the absorption of water from the contents of your intestines into the body.

This is why the most common symptom of gastroenteritis is watery diarrhoea and why dehydration (a lack of water in the body) is such a common complication.

How gastroenteritis is spread

Most types of gastroenteritis are highly infectious. The condition is mainly spread when bacteria found in faeces are transferred to your mouth.

Bacteria can be transferred 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 the contaminated object and then touch your face, or if you eat contaminated food, you may become infected by the virus or bacteria. Once infected, you will have the symptoms of gastroenteritis, such as vomiting and diarrhoea.

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

When to see Dr. B C Shah

In most cases, gastroenteritis does not need to be diagnosed because your symptoms should improve without treatment.

If your symptoms are severe or persist, Dr. B C Shah may take a stool sample so that it can be checked for specific bacteria or parasites. If a bacterium or parasite is identified, appropriate medication will be prescribed.

In some circumstances, blood tests and urine tests may be used to rule out other conditions, particularly if you are very unwell or if the symptoms last longer than usual.

Treating gastroenteritis

Most people with gastroenteritis only have mild symptoms and the infection passes after a few days without the need for treatment.

However, you may need treatment in hospital if your symptoms are severe, or if you are vulnerable because of your age or another illness. This is because diarrhoea can quickly cause dehydration which, if severe, can be fatal.

The dangers of dehydration mean that it is very important to replace fluids that are lost through vomiting and diarrhoea. You should drink at least 2 litres (3.5 pints) of water a day, plus 200ml (a third of a pint) of water after every episode of diarrhoea.

An oral rehydration solution can be used by people who are particularly vulnerable to the effects of dehydration, such as elderly people or those with another existing condition.

In severe cases of gastroenteritis, antidiarrhoeal medication or anti-emetics (anti-sickness medication) may be recommended.

Preventing gastroenteritis

As gastroenteritis is highly 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 vomiting or diarrhoea
  • Not sharing towels, flannels, cutlery or utensils with other members of your household
  • Not returning to work until 48 hours after your last bout of vomiting or diarrhoea

Symptoms of gastroenteritis

The symptoms of viral gastroenteritis usually begin 24–48 hours after you are infected. This time is called theincubation period.

The incubation period for bacterial gastroenteritis can range from 12 hours to 5 days, depending on the bacteria responsible.

Repeated episodes of diarrhoea are the most common symptom of gastroenteritis. Loose, watery stools are usually 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
  • A high temperature (fever) of 38–39C (100.4–102.2F)


Dehydration is where your body loses more fluid than you can take in. It is a very serious complication that can occur if fluid lost through vomiting and diarrhoea is not replaced.

Elderly people are particularly at risk from the effects of dehydration which, if not treated, can be fatal.

Therefore, you should be aware of symptoms that may suggest you or someone in your care is becoming dehydrated.

The 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

Find out more about treating dehydration.

When to seek medical advice

In most cases, medical treatment is not needed for gastroenteritis because the symptoms usually pass after a number of days (typically two to three days for viral gastroenteritis and four to seven days for bacterial gastroenteritis).

However, medical treatment may be required in some circumstances. Contact Dr. B C Shah if you have any of the following symptoms:

  • Vomiting that lasts for more than two days
  • An inability to keep liquid down for more than a day
  • Diarrhoea that lasts for more than three days
  • Blood in your vomit or 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 an inability to pass urine

Also seek medical advice if your symptoms do not begin to improve after three days, or if you think you got the infection while in 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 Dr. B C Shah if you have any risk factors that increase your risk of developing a serious complication from infections, such as:

Causes of gastroenteritis

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

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


Noroviruses are the most common cause of viral gastroenteritis in adults. Norovirus infections are sometimes referred to as “winter vomiting bugs” because they tend to be more widespread during the winter months. However, they can occur at any time of the year.

Norovirus outbreaks often occur in confined 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 coming into contact with an infected person or 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 you to get a norovirus infection several times. This is because after getting the illness, immunity to the virus only lasts for 14 weeks.

Food poisoning

Most cases of bacterial gastroenteritis are caused by food poisoning. Some cases of viral gastroenteritis can also be caused by food poisoning.

Food can become contaminated with a virus if it is handled by a person with a viral infection. Contamination can occur at any stage during the food’s production, processing or cooking.

For example, food poisoning can be caused by:

  • Not cooking food at the right temperature or for the right length of time
  • Not chilling food at the correct temperature
  • Someone who has not washed their hands properly handling the food
  • Eating food after it has reached its use by date
  • Cross-contamination (see below)


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 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 in the fridge. The meat juices may drip onto the meals and contaminate them.

The most common types of bacteria that are 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

Traveller’s diarrhoea

Traveller’s diarrhoea refers to gastroenteritis that develops after travelling abroad. It can be caused by a range of different bacteria or parasites such as:

  • The shigella bacterium or the entamoeba parasite – these are both spread through poor hygiene and cause a type of traveller’s diarrhoea called dysentery
  • Cryptosporidium – a parasite found in soil, food or water that has been contaminated with animal or human faeces
  • Giardia intestinalis – a parasite found in water that has been contaminated with animal or human faeces (infections that are caused by this parasite are known as giardiasis)

Treating gastroenteritis

Most cases of gastroenteritis do not require treatment and the symptoms will improve after a few days. Medicationmay be needed in severe cases.

Information on self care and medication is outlined below.

Self care

If you have gastroenteritis, it is very important to replace any fluids that your body loses through vomiting and diarrhoea. Drink at least 2 litres (3.5 pints) of water a day, plus 200ml (a third of a pint) of water every time you pass diarrhoea.

Oral rehydration salts are recommended for people who are vulnerable to the effects of dehydration, such as elderly people or those with another existing condition.

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

Some types of oral rehydration salts may not be suitable if you have a kidney condition. Dr. B C Shah will be able to give you further advice about this.

Try to maintain a normal, healthy diet. Avoid eating foods that are high in fat and sugar because they could make your symptoms worse. You will be able to tolerate light, plain foods, such as rice or wholemeal bread, better than spicy or rich foods.

It may be better to eat six light meals a day rather than three large meals.


Unless your symptoms are severe, medication to treat gastroenteritis is not usually needed. The medications that are used to treat the symptoms of gastroenteritis are outlined below.

Antidiarrhoeal medications

Antidiarrhoeal medications are used to treat the symptoms of diarrhoea. Loperamide is a widely used antidiarrhoeal medication for treating gastroenteritis.

Loperamide slows down the movement of your bowel contents and can also increase water absorption from the gut.

Constipation and dizziness are two common side effects of loperamide. Rarer side effects include:

  • Cramps
  • Drowsiness
  • Rashes
  • Bloating

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

You should not take loperamide, or any other antidiarrhoeal medication, if you have a high temperature of 38C (100.4F) or above, or if you have blood or mucus in your stools. In these instances, the medication could make your symptoms worse.

Antidiarrhoeal medication should not be used by children under 12 years of age, unless directly instructed by Dr. B C Shah.

Anti-emetic medications

Anti-emetic medications are used to help prevent or reduce vomiting.

Common anti-emetics include stemetil (prochlorperazine) and metoclopramide (which can be given by injection directly into your muscles as well as orally).

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


Antibiotics are not usually recommended for treating gastroenteritis because:

  • Most gastroenteritis cases 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 antibiotics are used to treat mild conditions, they become less effective at treating more serious conditions

However, antibiotics may be recommended if you have particularly severe gastroenteritis and a specific bacteria has been identified as the cause.

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

Side effects of using antibiotics to treat gastroenteritis include:

  • Nausea
  • Vomiting
  • Diarrhoea
  • Stomach pain
  • 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 mean that you are unable to keep down any fluids
  • You have symptoms that suggest severe dehydration, such as not passing any urine

Treatment in hospital will involve administering fluids and nutrients intravenously (directly into a vein).

Preventing gastroenteritis

As gastroenteritis is very infectious, it is important to take steps to prevent it from spreading to other people.

Controlling the infection

To prevent the spread of infection:

  • Wash your hands thoroughly after going to the toilet and before eating or preparing food.
  • Clean the toilet, including the seat and handle, with disinfectant after each bout of vomiting or diarrhoea.
  • Don’t share towels, flannels, cutlery and utensils with other household members.
  • Don’t return to work until 48 hours have passed since your last bout of vomiting or diarrhoea.

Food hygiene

Practising good food hygiene will help you avoid getting gastroenteritis from food poisoning. You should:

  • Regularly wash your hands, surfaces and utensils with hot, soapy water.
  • Never store raw and cooked foods together.
  • Make sure that food is properly refrigerated.
  • Always cook your food thoroughly.
  • Never eat food that is past its sell by date.

Traveller’s 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 is usually safe includes:

  • Sealed bottled water produced by a recognised international manufacturer
  • Cooked food, such as soup or a stir-fry
  • Canned food or food in sealed packs
  • Fresh bread
  • Unpeeled fruit
  • Tea or coffee
  • Alcohol

Before travelling, ensure you have the travel vaccinations recommended for the country you are visiting.

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