The flu is most dangerous for the young, elderly, and people with chronic health conditions. The CDC estimates that 24,000 Americans die each year from the flu. Photo Credit, McFarland.

Nationwide, the flu has spread to more than 80% of the U.S. The latest weekly flu advisory report from the Centers for Disease Control and Prevention indicates that 41 states have widespread influenza activity--an increase of 31 states from the previous week.

The CDC will issue a flu update Friday.

Read more on the worsening flu season here.

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