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[[File:Flu und legende.jpg|right|240px]]
[[File:Flu und legende.jpg|right|240px]]
'''Influenza''' or '''flu''' is a highly contagious respiratory disease caused by influenza [[virus]]es. It is spread through human contact, and from contact with infected birds, pigs or other animals. Winter is the worst season. Influenza caused a deadly worldwide pandemic in 1918-1919, as populations were weakened in the aftermatch of World War I. Over 20 million died worldwide. A worldwide "swine flu" epidemic is underway in 2009, caused by a new strain; so far the deaths from the new strain have been few.
'''Influenza''' or '''flu''' is a highly contagious respiratory disease caused by influenza [[virus]]es. It is spread through human contact<ref>It can be spread from contact with infected birds, pigs or other animals.</ref>. Winter is the worst season. Influenza caused a deadly worldwide pandemic in 1918-1919, as populations were weakened in the aftermatch of World War I. Over 20 million died worldwide.
A worldwide H1N1 "swine flu" epidemic is underway in 2009, caused by a new strain; so far the deaths from the new strain have been few. It is highly infectious and people with the symptoms should stay home.
==Medical==
==Medical==
Flu can cause mild to severe illness, and at times can lead to death. In normal years in the U.S. on average 5% to 20% of the population catches the flu; more than 200,000 people are hospitalized from flu complications, and about 36,000 people die from flu-related causes. Victims who are over age 70, young children, and people with certain health conditions, are at high risk for serious flu complications.
===Telling the difference between flu and a common cold===
The flu is different from a cold. The flu usually comes on suddenly and may include these "flu-like" symptoms:
The flu is different from a cold. The flu usually comes on suddenly and may include these "flu-like" symptoms:
* High Fever
* High Fever
* Muscle aches
* Muscle aches
* Stomach symptoms, such as nausea, vomiting, and diarrhea, also can occur but are more common in children than adults
* Stomach symptoms, such as nausea, vomiting, and diarrhea, also can occur but are more common in children than adults
====Fever====
====Fever====
Fever is rare with a cold. <br>
Fever is rare with a cold. <br>
Sore throat is not commonly present with the flu.
Sore throat is not commonly present with the flu.
==When Flu Occurs==
==Seasons==
The peak of flu season is winter. The overall health impact (e.g., infections, hospitalizations, and deaths) of a flu season varies from year to year. Seasons are more likely to be severe if the epidemic originates in China. The U.S. [[Center for Disease Control]] monitors circulating flu viruses and their related disease activity and provides influenza reports each week from October through May.
The peak of flu season is winter. The overall health impact (e.g., infections, hospitalizations, and deaths) of a flu season varies from year to year. Seasons are more likely to be severe if the epidemic originates in China. The U.S. [[Center for Disease Control]] monitors circulating flu viruses and their related disease activity and provides influenza reports each week from October through May.
==Contagion==
==Contagion==
The period when an infected person is contagious depends on the age and health of the person. Studies show that most healthy adults may be able to infect others from 2 days prior to becoming sick and for 10 days after they first develop symptoms. Some young children and people with weakened immune systems may be contagious for longer than a week. Infectivity also varies widely between people, with about one in ten being "hyper-infectors" who are responsible for the majority of influenza transmission. While each flu season is unique, it is estimated that, on average, approximately 5% to 20% of people get the flu each year, and more than 200,000 persons are hospitalized for flu-related complications each year. About 36,000 people die on average per year from the complications of flu.
The period when an infected person is contagious depends on the age and health of the person. Studies show that most healthy adults may be able to infect others from 2 days prior to becoming sick and for 10 days after they first develop symptoms. Some young children and people with weakened immune systems may be contagious for longer than a week. Infectivity also varies widely between people, with about one in ten being "hyper-infectors" who are responsible for the majority of influenza transmission. While each flu season is unique, it is estimated that, on average, approximately 5% to 20% of people get the flu each year, and more than 200,000 persons are hospitalized for flu-related complications each year. About 36,000 people die on average per year from the complications of flu.
== Types ==
== Types ==