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Influenza is an infection of the upper respiratory tract (airways), commonly known as flu.
Influenza, also known as flu, is a highly contagious viral disease that tends to occur in epidemics during the winter. The infection mainly affects the upper respiratory tract (airways) and can be transmitted easily in airborne droplets from the coughs and sneezes of infected people. Influenza viruses can also be transmitted from person to person through direct contact.
Many different viral infections can result in mild flu-like symptoms, but true influenza is caused by two principal types of influenza virus: A and B. The type A virus, in particular, often changes its structure (mutates) and produces new strains to which very few people have immunity.
The number of influenza cases varies from year to year, but particularly virulent strains can spread worldwide and cause millions of deaths in major outbreaks, known as pandemics. Twentieth century pandemics include Spanish flu in 1918, Asian flu in 1957, Hong Kong flu in 1968, and Russian flu in 1977.
What are the symptoms of influenza (flu)?
The symptoms of influenza develop 24-48 hours following infection. Many people believe that they have influenza when they have only a common cold, but the symptoms of influenza are far more severe than those of a cold. The first symptom may be slight chills. Other symptoms, which develop later and worsen rapidly in just a few hours, may include the following:
- High fever, sweating, and shivering.
- Aching muscles, especially in the back.
- Severe exhaustion.
- Frequent sneezing, stuffy or runny nose, sore throat, and cough.
Following an attack of flu, tiredness and depression are often experienced after other symptoms have disappeared.
The most common complications are bacterial infections of the airways (see Acute bronchitis) and lungs (see Pneumonia). Such infections can be life-threatening to people in certain high-risk groups. These include babies, elderly people, those with long-term heart or lung disease, and people with reduced immunity, such as those with AIDS (see HIV infection and AIDS) or diabetes mellitus.
What might be done?
For most normally healthy people, the best way to relieve the symptoms of influenza is to rest in bed, drink plenty of cool fluids, and follow the advice for bringing down a fever. Painkillers, such as paracetamol, and other over-the-counter remedies may help (see Cold and flu remedies). However, you should see your doctor immediately if you have difficulty in breathing or if your fever lasts for longer than 2 days. Your doctor may arrange for you to have a chest X-ray to rule out the possibility of a chest infection, such as pneumonia. If a bacterial infection is found, your doctor will prescribe antibiotics. However, these drugs have no effect on the influenza virus itself.
Elderly people; those with heart or circulatory problems, chronic kidney disease, chronic lung conditions (such as chronic obstructive pulmonary disease and asthma); and people with reduced immunity (including those with diabetes) are at increased risk of serious complications. A doctor should be consulted immediately when the symptoms of influenza first appear in such people. He or she may prescribe antiviral drugs, such as zanamivir or oseltamivir. This treatment should be started within 48 hours of the onset of symptoms, but the earlier the better.
What is the prognosis?
If no complications occur, most symptoms of influenza usually disappear after 6-7 days, although a cough may persist for over 2 weeks and tiredness may last longer. However, for people in high-risk groups, the complications of influenza may be life-threatening, and, in epidemics, deaths from associated pneumonia are very common.
Immunization can give effective protection. It is recommended for elderly people, those (excluding babies under 6 months) in high-risk groups, and those likely to be exposed to influenza, such as health workers or carers of the elderly.
Immunization prevents infection in about two-thirds of people who are vaccinated annually. However, the vaccine can never be completely effective because the viruses frequently mutate, and different strains are responsible for outbreaks each year. During a flu outbreak, some people in high-risk groups may also be prescribed the antiviral drug oseltamivir. This drug may not always prevent the illness but may reduce its severity and duration.
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