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Gastric flu - Introduction

NHS Choices Medical Reference

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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).

Read more about the symptoms of gastroenteritis.

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

What causes gastroenteritis in adults?

In England, 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.

Read more about the causes of gastroenteritis.

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 your GP

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

If your symptoms are severe or persist, your GP 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.

Read more about treating gastroenteritis.

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

Read more about preventing gastroenteritis.

Medical Review: May 08, 2012
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