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Flu - symptoms and diagnosis

Flu (influenza) is a severe infection caused by a virus. The flu virus infects your lungs and upper airways. 

Flu is unpredictable. If you are young and healthy, you will usually feel unwell for a week but, you will not need to see your GP. Most flu can be treated at home.

Antibiotics do not work on flu. Getting lots of rest and drinking plenty of liquids will make you feel better.

Most people who think they have the flu usually just have a cold.

The real flu tends to happen during the winter. It usually spreads between October and April.

Some people are at risk of the serious complications of flu.

People at risk of complications include:

  • people aged 65 and over
  • pregnant women
  • people with a long term medical condition

You can see a list of other at-risk groups here.

If you have flu and you are at risk of the complications of flu, you should contact your GP. You may need special anti-viral medicines. These work best if started within 48 hours of flu symptoms.

Symptoms

Flu symptoms come on very quickly and you get  muscle aches and a high fever. Headache is very common. You will feel extremely weak and may find it hard to even get out of bed. After a few days, you may develop a cough. 

Flu symptoms can also include:

  • sore throat
  • difficulty sleeping
  • loss of appetite
  • diarrhoea or tummy pain
  • nausea and vomiting

The symptoms are similar for children. But they can also get pain in their ear and may be less active than usual.

Diagnosis

It is useful to know the difference between a cold and the flu.

Flu symptoms:

  • come on suddenly
  • start with a fever, muscle aches, headache, weakness and fatigue

Cold symptoms:

  • usually come on gradually
  • start with a sore throat and a blocked or a runny nose.

Symptoms of a cold are generally mild compared to flu.

Complications

For most people, flu is just a bad experience. But for others, it can lead to more serious illness. Some complications of flu can be life threatening.

If you are aged 65 years or older, pregnant, or if you have a long term medical condition are on medication, you have an increased risk of serious complications from the flu. You may need special anti-viral medicines. These work best if started within 48 hours of flu symptoms.

The most common complication is pneumonia. Other complications include bronchitis and ear infections.

Flu can also worsen existing conditions such as:

  • asthma
  • chronic obstructive pulmonary disease (COPD)
  • heart failure

Related topic

Vaccines needed during pregnancy - flu vaccine

page last reviewed: 12/06/2019
next review due: 12/06/2022