Flu (Influenza)

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Overview

Flu is an acute illness (i.e., comes on suddenly) caused by infection with an influenza virus. The flu affects the upper and lower respiratory tract (e.g., nose, throat, bronchi, lungs) and also causes symptoms that affect the entire body (i.e., systemic symptoms), such as headache, fever, muscle aches (myalgia), and weakness. Infection with the flu virus usually lasts about one week.

Influenza can cause mild to severe illness. In some cases, the flu can cause death. Young children, the elderly, and patients who have certain medical conditions (e.g., heart, lung, or kidney problems, diabetes, cancer) are at increased risk for developing serious complications from the flu. The best way to avoid influenza infection is to receive a flu vaccination each year.

The flu is more common in the winter months, and outbreaks of the illness occur nearly every year throughout the world. The extent and severity of influenza outbreaks vary considerably from year to year and from location to location. Serious local outbreaks generally occur about every 1–3 years, and global outbreaks (pandemics) occur every 10–15 years.

Pandemics result from minor genetic changes to the influenza virus. Examples of pandemic flu include the "Spanish flu" in 1918–1919, the "Asian flu" in 1957, and the "Hong Kong flu" in 1968. The Spanish flu pandemic may have resulted in as many as 40 million deaths worldwide.

Incidence and Prevalence
According to the Centers for Disease Control and Prevention (CDC), 5–20% of the population is infected with the flu each year in the United States. The CDC also reports that in the United States, more than 200,000 people are hospitalized with the flu and about 36,000 people die from flu complications each year.

The World Health Organization (WHO) reports that throughout the world, annual outbreaks result in 3–5 million severe cases and between 250,000 and 500,000 deaths. In the United States, most deaths from the flu occur in people over the age of 65.

In tropical areas of the world, the flu occasionally causes year-round outbreaks. These outbreaks often are severe and result in widespread infection.

Flu (Influenza), Overview reprinted with permission from fluchannel.com
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