Many viruses can cause a flu-like illness. There is usually a seasonal outbreak of influenza (flu) in the UK each winter. Flu-like illnesses typically cause a fever, aches and pains in muscles and joints, a cough and various other symptoms. Most people recover fully, but complications such as pneumonia can sometimes develop. Complications are sometimes serious. Every year some people die from the complications of flu. If you are at increased risk of developing complications, you should be immunised against seasonal flu (have a flu jab) each autumn.
What are flu and flu-like illnesses?
Influenza (flu) is caused by the influenza virus. However, many other viruses can cause an illness similar to flu. It is often difficult to say exactly which virus is causing the illness, so doctors often diagnose a flu-like illness.
There are three types of influenza virus - A, B and C. Influenza A and B cause most of the cases of influenza. Each winter a different type of influenza virus causes an outbreak of flu which affects many people. This is called seasonal flu. If you get a flu-like illness during an outbreak of seasonal flu, it is likely to be caused by the prevailing influenza virus. Most cases of influenza usually occur in a period of six to eight weeks during the winter.
Swine flu is caused by a particular strain of influenza A virus which is called influenza A virus (H1N1v). It seems to affect children and young adults more commonly than those over the age of 60 years. Most people with this type of influenza have a mild flu-like illness. You are more likely to have sickness and/or diarrhoea with this type of influenza.
Note: bird flu (avian influenza) is different and is more serious.
What are flu symptoms (or flu-like illness symptoms)?
Common flu symptoms in adults and older children include: high temperature (fever), sweats, aches and pains in muscles and joints, a dry cough, sore throat, sneezing, and headache. You may also feel sick. The illness caused by the influenza virus tends to be worse than illnesses caused by other viruses which cause a flu-like illness. Even if you are young and fit, flu can make you ill enough to need to go to bed.
Common flu symptoms in babies and young children include: high temperature, sweats, a cough, sore throat, sneezing, difficulty in breathing, lethargy and poor feeding. Some young children have a febrile convulsion (fit) when they have flu.
Typically, symptoms are at their worst after 1-2 days. Then they usually gradually ease over several days. An irritating cough may persist for a week or so after other symptoms have gone. Most people recover completely within two to seven days.
How do you catch flu?
Flu is passed from person to person by droplets created when someone with the infection sneezes or coughs. You can also catch it by touching a surface where the virus has been deposited. Flu can spread quickly in these ways.
What else could my symptoms be due to?
Other serious illnesses can have similar symptoms to flu when they first develop - for example, meningitis, malaria, or pneumonia. If you have a more serious illness, other symptoms usually develop in addition to those mentioned above.
Symptoms to look out for which may mean that you have a different and more severe illness include:
Note: it is important to tell a doctor if you have flu-like symptoms and you have been to a country within the last year where malaria is present. Initial symptoms of malaria can be similar to flu.
What is the treatment for flu and flu-like illnesses?
Your immune system will usually clear viruses that cause flu and flu-like illnesses. Treatment aims to ease symptoms until the infection goes, and to prevent complications. Treatment consists of general measures, antiviral medication in some situations, antibiotics in some situations and admission to hospital for the small number of people who become very ill (usually because a complication develops).
Stay at home as much as possible to prevent passing on the infection.
Paracetamol and/or ibuprofen can lower your temperature, and also ease aches and pains. Drink plenty of fluids to prevent dehydration. It is best not to smoke. Decongestant drops, throat lozenges and saline nose drops may be helpful to ease nose and throat symptoms.
Note: parents and carers should not use over-the-counter cough and cold medicines in children under 6 years old. There is no evidence that they work and they can cause side-effects such as allergic reactions, effects on sleep or even hallucinations.
Antiviral medicines called oseltamivir (trade name Tamiflu®) and zanamivir (trade name Relenza®) are sometimes used. Antiviral medicines do not kill the virus but interfere with the way the virus multiplies. Antiviral medicines do not cure flu, or offer long-term protection against flu. If you do not have an antiviral medicine you are still likely to make a full recovery. However, antiviral medicines reduce the risk of developing complications. They may also reduce the severity and duration of symptoms by a day or two.
An antiviral medicine may be prescribed if you are at increased risk of developing complications when you have flu (see list below). Treatment is usually taken for five days. GPs are only allowed to prescribe an antiviral medicine when national surveillance schemes show there is a lot of influenza in the community. An antiviral medicine is also often used in people who are admitted to hospital with flu.
Medication may also be prescribed to certain people to prevent flu - for example, if you live in a residential home and there is an outbreak of flu in the home. It is also given if you are at increased risk of complications and have been in close contact with a person with flu.
To give the most benefit, antiviral medicines need to be taken soon after symptoms begin (usually within 48 hours).
Antibiotics kill bacteria, but not viruses. Therefore, they are not routinely prescribed for viral illnesses such as flu or flu-like illnesses. However, they may be used if a complication develops like a secondary bacterial chest infection or pneumonia (see below).
Admission to hospital
A small number of people with flu become ill enough to need hospital admission. This is usually because they have developed complications from flu.
What are the possible complications of flu and flu-like illnesses?
If you are normally well, then you are unlikely to develop complications. You are likely to recover fully. However, see a doctor if symptoms change or become worse. Complications are more likely to develop if you are in any of the at-risk groups listed below.
The most common complication is a bacterial chest infection. This may develop in addition to the viral infection (that is, a secondary infection). This can sometimes become serious and develop into pneumonia. A course of antibiotics will often cure this. However, a bacterial infection can sometimes become life-threatening, particularly in those who are frail or elderly.
Note: with flu or a flu-like illness it is common to have a cough that lingers for 1-2 weeks after other symptoms have gone. Green sputum does not necessarily mean that you have a secondary chest infection. The symptoms to look out for that may indicate a secondary chest infection include: a recurrence of a high temperature, worsening of cough, shortness of breath, fast breathing, and chest pain.
Other complications that sometimes occur include a sinus infection and an ear infection. Other serious complications are rare, such as brain inflammation (encephalitis).
Who should be immunised against the seasonal flu virus?
Seasonal flu is the strain of flu virus that arrives in the UK each autumn. The actual strain varies from year to year. A new vaccine (often called the flu jab) is developed each year to protect against the strain that is most common that year. The 2012-2013 flu vaccine will also provide protection against the influenza A viral (H1N1v) strain.
The flu vaccine will protect 7-8 out of 10 people against infection with flu. It takes up to 14 days for full protection to be reached after having the vaccine. This protection lasts for around one year. The flu vaccine has also been shown to reduce the risk of developing a complication from flu, especially in the elderly.
The Department of Health (DH) issues advice on who should be immunised. This is reviewed from time to time. The aim is to protect people who are more likely to develop complications from flu. Current advice is that you should be immunised against the seasonal flu virus each autumn if you:
In addition to the main at-risk groups of people listed above:
Note: people who work in close contact with poultry are no longer thought to be at increased risk.
If you are healthy, aged under 65 and do not fall into any of the above categories, then you do not need immunisation against seasonal flu. This is because you are unlikely to develop complications from flu