Influenza (also known as the flu) is a contagious respiratory illness caused by flu viruses. It can cause mild to severe illness. The flu comes on suddenly. According to the Centers for Disease Control and Prevention, flu symptoms include:
- Fever or feeling feverish/chills (Note: not everyone will have a fever.)
- Sore throat
- Runny or stuffy nose
- Muscle or body aches
Some people could develop complications from the flu. Examples include:
How Flu Spreads
According to the CDC, people with flu can spread it to others up to about 6 feet away. It usually occurs when people cough, sneeze or talk. Less often, a person might also get flu by touching a surface or object and then touching their own mouth or nose.
You can infect someone one day before symptoms develop and up to 5-7 days after. Children may pass the virus for longer than seven days. Symptoms start one to four days after the virus enters the body. Some persons can be infected but have no symptoms. You can still spread the virus to others.
Some Years Worse Than Others
The scenarios above usually occur during conventional or seasonal flu season. However, there are situations in which some flu outbreaks are severe. For example, in 2009-2010, a new and very different flu virus (called 2009 H1N1) spread worldwide causing the first flu pandemic in more than 40 years.
Causes of the Flu
Influenza viruses cause the flu and are divided into three types, designated A, B, and C. Influenza types A and B are responsible for epidemics of respiratory illness that occur almost every winter and are often associated with increased rates of hospitalization and death. Influenza type C is a bit of a step-child to A and B, posing no severe public-health impact.