What is flu?
Flu (short for “influenza”) is a very contagious disease of the body’s respiratory (breathing) system. Flu is spread when an infected person sneezes, coughs or talks, spraying flu virus into the air. People nearby can then breathe in the virus. Flu often spreads among families and co-workers. Flu symptoms usually start 1 to 3 days after a person breathes in the virus. Flu symptoms include sudden fever, cough, muscle aches, headache and general weakness. Flu also usually causes runny nose and sore throat. These symptoms can range from very mild to very severe. Most people are sick for only a few days. Some people, however, may develop pneumonia. Every year in the U.S., flu causes thousands of hospital admissions, mostly among the elderly, pregnant women and people with chronic medical problems and weakened immune systems.
