Definition of Flu:

The flu is an infection of the nose, throat, and lungs. The influenza virus causes the infection.

See also: Swine flu (H1N1)

Causes, incidence, and risk factors:

Influenza A usually arrives between early winter and early spring. Influenza B can appear at any time of the year. H1N1, or swine flu, is another type of influenza.

Most people catch the flu when they breathe in tiny droplets from coughs or sneezes of someone who has the flu. It is also spread when you touch a something with the virus on it, then touch your mouth, nose, or eyes.

Symptoms appear 1 - 7 days later (usually within 2 - 3 days). The flu spreads easily. It often strikes a community all at once. Students or workers become sick within 2 or 3 weeks of the flu's arrival in a school or workplace.

Sometimes people confuse colds and flu. They do share some of the same symptoms. Most people get a cold several times each year. But they usually get the flu once every few years.

Click here to see a video about the difference between a cold and the flu.

People call a viral illness that makes them throw up or have diarrhea "stomach flu." This is incorrect. The flu does not cause the stomach symptoms. The flu mostly causes symptoms in the nose, throat, and lungs.