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Gastric flu - Symptoms of gastroenteritis

NHS Choices Medical Reference

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The symptoms of viral gastroenteritis usually begin 24-48 hours after you are infected. This time is





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 your GP 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 your GP if you have any risk factors that increase your risk of developing a serious complication from infections, such as:

Medical Review: May 08, 2012
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