Flu is an infectious and common viral illness spread by coughs and sneezes.

It's not the same as the common cold. Flu is caused by a different group of viruses. Symptoms tend to be more severe and last longer.

You can catch flu – short for influenza – all year round, but it is especially common in winter, which is why it is also known as "seasonal flu".

Flu causes a sudden high temperature, headache and general aches and pains, tiredness and a sore throat. You can also lose your appetite, feel nauseous and have a cough.

Flu symptoms can make you feel so exhausted and unwell that you have to stay in bed and rest until you feel better.

All types of flu have similar symptoms. Although the flu and common cold have similar symptoms, the flu tends to be more severe.

Flu can be various types :

1. Seasonal flu
2. Viral flu like H7N9 flu, H3N2v flu, H1N1 swine flu, H5N1 bird flu etc.
3. Cold flu

The flu and the common cold have similar symptoms. It can be difficult to tell the difference between them. In general, the flu is worse than the common cold. Symptoms such as fever, body aches, tiredness, and cough are more common and intense with the flu. People with colds are more likely to have a runny or stuffy nose.

Symptoms:

Flu symptoms include:

1. A 100^oF or higher fever or feeling feverish (not everyone with the flu has a fever)
2. A cough and/or sore throat
3. A runny or stuffy nose
4. Headaches and/or body aches
5. Chills
6. Fatigue
7. Nausea, vomiting, and/or diarrhea (most common in children)

Seek medical attention immediately if you experience any of the following:

1. Difficulty breathing or shortness of breath
2. Purple or blue discoloration of the lips
3. Pain or pressure in the chest or abdomen
4. Sudden dizziness
5. Confusion
6. Severe or persistent vomiting
7. Seizures
8. Flu-like symptoms that improve but then return with fever and worse cough

When to see a doctor

If you are otherwise fit and healthy, there is usually no need to see a doctor if you have flu-like symptoms. 

The best remedy is to rest at home, keep warm and drink plenty of water to avoid dehydration.

You can take paracetamol or ibuprofen to lower a high temperature and relieve aches.

You should see a doctor if you have flu-like symptoms and you:

1. are 65 or over
2. are pregnant
3. have a long-term medical condition such as diabetes, heart disease, lung disease, kidney disease or a neurological disease
4. have a weakened immune system

This is because flu can be more serious for you and your doctor may want to prescribe antiviral medication.

Antiviral medicine can lessen the symptoms of flu and shorten its duration, but treatment needs to begin soon after flu symptoms start for it to be effective.

Antibiotics are of no use in the treatment of flu because it is caused by a virus and not by bacteria.

How long does flu last?

If you have flu, you generally start to feel ill within a few days of being infected.

Symptoms peak after two to three days and you should begin to feel much better after a week or so, although you may feel tired for much longer.

You are usually infectious – that is, able to pass flu on to others – a day before your symptoms start and for a further five or six days. Children and people with weaker immune systems, such as cancer patients, may remain infectious for longer.

Elderly people and anyone with certain long-term medical conditions are more likely to have a bad case of flu, and are also more likely to develop a serious complication such as a chest infection.

Preventing the spread of flu

The flu virus is spread in small droplets of fluid coughed or sneezed into the air by an infected person. These droplets can travel a metre or so and infect anyone within range who breathes them in.

Flu can also spread if someone with the virus transfers it on their fingers. For example, if you have flu and you touch your nose or eyes and then touch someone else, you may pass the virus on to them.

Similarly, if you have flu and touch hard surfaces such as door handles with unwashed hands, other people who touch the surface after you can pick up the infection.

You can stop yourself catching flu or spreading it to others by being careful with your hygiene. 

Always wash your hands regularly with soap and water, as well as:

1. regularly cleaning surfaces such as your keyboard, telephone and door handles to get rid of germs
2. using tissues to cover your mouth and nose when you cough or sneeze
3. putting used tissues in a bin as soon as possible

You can also help stop the spread of flu by avoiding all unnecessary contact with other people while you're infectious. You should stay off work until you are no longer infectious and feeling better.

The flu vaccine

A flu vaccine is available free on the NHS for:

1. pregnant women
2. children aged two and three
3. children aged 2 to 18 with a long-term health condition
4. adults aged 65 or older
5. people with a serious medical condition
6. healthcare workers or carers
7. people living in a residential or nursing home

Despite popular belief, the flu vaccine cannot give you flu as it doesn't contain the active virus needed to do this.