The flu

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Normal lung anatomy

Influenza

Nasal spray flu vaccine

The flu

Definition:

The flu is a contagious infection of the nose, throat, and lungs caused by the influenza virus.

Alternative Names:
Flu; Influenza A; Influenza B
Causes, incidence, and risk factors:

The flu usually begins abruptly, with a fever between 102 to 106F. (An adult typically has a lower fever than a child.) Other common symptoms include a flushed face, body aches, and lack of energy. Some people have dizziness or vomiting. The fever usually lasts for a day or two, but can last 5 days.

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Somewhere between day 2 and day 4 of the illness, the "whole body" symptoms begin to subside, and respiratory symptoms begin to increase. The flu virus can settle anywhere in the respiratory tract, producing symptoms of a cold, croup, sore throat, bronchiolitis, ear infection, or pneumonia.

The most prominent of the respiratory symptoms is usually a dry, hacking cough. Most people also develop a sore throat andheadache. Nasal discharge (runny nose) and sneezing are common. These symptoms (except the cough) usually disappear within 4-7 days. Sometimes, thefever returns. Cough and tiredness usually last for weeks after the rest of the illness is over.

The flu usually arrives in the winter months. The most common way to catch the flu is bybreathing indroplets from coughs or sneezes. Less often, it is spread when you touch a surface such as a faucet handle or phone that has the virus on it, and then touch your own mouth, nose, or eyes.

Symptoms appear 1-7 days later (usually within 2-3 days). Because the flu spreads through the air and isvery contagious, it often strikes a community all at once. This creates a cluster of school and work absences. Within 2 or 3 weeks of its arrival in a school, many student have become sick.

Tens of millions of people in the United States get the flu each year. Most get better within a week or two, but thousands become sick enough to be hospitalized. About 36,000 people died each year from complications of the flu.

Anyone at any age can have serious complications from the flu, but those at highest risk include:

People over 50
Children between 6 months and 2 years
Women more than 3 months pregnant during the flu season
Anyone living in a long-term care facility
Anyone with chronic heart, lung, or kidney conditions, diabetes, or weakened immune system

Sometimes people confuse cold and flu, which share some of the same symptoms and typically occur at the same time of the year. However, the two diseases are very different. Most people get a cold several times each year, and the flu only once every several years.