Influenza
Flu
What is Flu?
Flu is a virus that causes flu attacks the respiratory system — the nose, throat and lungs. After the virus enters the body, it begins to multiply inside cells lining the airways. The immune system tries to fight off the infection, a defensive response that produces most flu symptoms.
Sometimes the flu can make people extremely sick. An out-of-control immune response can lead to significant tissue damage in the lungs. Also, an immune system overwhelmed by flu infection is vulnerable to secondary infection, usually by bacteria, which can trigger an extreme inflammatory response that damages multiple organs.
Causes of flu
The virus that causes flu spreads from person to person through tiny droplets that enter the air when an infected person sneezes or coughs. It is also possible to pick up the virus by touching an infected surface.