Gastric flu - Symptoms of gastroenteritis in adults

Depending on the specific cause, the symptoms of gastroenteritis can take anything between a few hours and a few days to develop after you are infected.

The main symptom is repeated diarrhoea, which may sometimes contain traces of blood or mucus.

Other symptoms can include:

vomiting
feeling sick
loss of appetite
stomach cramps
aching limbs
headaches
a high temperature (fever)

Signs of dehydration

Gastroenteritis can cause dehydration, which can be more serious than the infection itself. Elderly people are particularly at risk from the effects of dehydration, which, if not treated, can be fatal.

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

Signs of mild dehydration can include:

thirst or a dry mouth
dark-coloured urine
dizziness and lightheadedness, particularly after standing up
feeling sick
lack of energy
headaches

Signs of more severe dehydration can include:

weakness and apathy (a lack of emotion or enthusiasm)
muscle cramps
pinched face
sunken eyes
passing little or no urine
confusion
rapid heartbeat

When to seek medical advice

In most cases, there's no need to see your doctor if you have gastroenteritis because the symptoms usually pass in a few days without any specific treatment.

However, you should contact your GP if:

your symptoms do not begin to improve after a few days
repeated episodes of vomiting mean that you are unable to keep down any fluids
there is blood or mucus in your stools
you have signs of more severe dehydration (see above)
you think you may have been infected while travelling in a part of the world with a poor standard of water hygiene in the previous few weeks
you are over 65 years of age
you are pregnant
you have a bowel disease, such as Crohn's disease or ulcerative colitis
you have a weakened immune system caused by another condition, such as HIV, or as the result of medical treatment, such as chemotherapy

If your GP is unavailable, contact your local out-of-hours service or call NHS 111 for advice.