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What Is the Flu?

Worried about catching the flu? Want to learn some ways to prevent it? Then read on to learn more about influenza -- what it is, how it's spread, and who's at greatest risk for getting it. Knowledge is power when it comes to preventing flu!

What is the flu?

Influenza, commonly known as the "flu," is an extremely contagious respiratory illness caused by influenza A or B viruses. Flu appears most frequently in winter and early spring. The flu virus attacks the body by spreading through the upper and/or lower respiratory tract.

What's the difference between a cold and flu?

The common cold and flu are both contagious viral infections of the respiratory tract. Although the symptoms can be similar, flu is much worse. A cold may drag you down a bit, but the flu can make you shudder at the very thought of getting out of bed.

Congestion, sore throat, and sneezing are common with colds. Both cold and flu bring coughing, headache, and chest discomfort. With the flu, though, you are likely to run a high fever for several days and have body aches, fatigue, and weakness. Symptoms of the flu also tend to come on abruptly. Usually, complications from colds are relatively minor, but a severe case of flu can lead to a life-threatening illness such as pneumonia.

More than 100 types of cold viruses are known, and new strains of flu evolve every few years. Since both diseases are viral, antibiotics cannot conquer cold or flu. Remember: Antibiotics only treat bacterial infections.

Two antiviral medications are available to treat flu. But there are no medications that specifically defeat the common cold. Antibiotics may be helpful only if there is a secondary bacterial infection.

For in-depth information, see WebMD's Flu Treatment.

How are stomach flu and influenza different?

"Stomach flu" is a popular term, but not a true medical diagnosis. It's not uncommon to mistake gastroenteritis, which is what stomach flu is, for the viral infection we commonly call the "flu." Gastroenteritis refers to inflammation of the gastrointestinal tract (stomach and intestines). Viruses are the most common cause of stomach flu. With gastroenteritis, you may have symptoms such as abdominal cramps, nausea, vomiting, and diarrhea.

For more about gastrointestinal flu, read WebMD's Stomach Flu or Influenza?

How is flu spread?

The flu virus is spread from person to person through respiratory secretions and typically sweeps through large groups of people who spend time in close contact, such as in daycare facilities, classrooms, college dormitories, military barracks, offices, and nursing homes.

Flu is spread when you inhale droplets in the air that contain the flu virus, make direct contact with respiratory secretions through sharing drinks or utensils, or handle items contaminated by an infected person. In the latter case, the flu virus on your skin can infect you when you touch or rub your eyes, nose, or mouth. That's why frequent and thorough handwashing is a key way to limit the spread of influenza. Flu symptoms start to develop from one to four days after infection with the virus.

WebMD Medical Reference

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