The flu is now widespread in about half of the Unite States, according to the Centers for Disease Control and Prevention.
The hardest hit states include Oregon and Nevada. California has seen regional flu outbreaks.
Medical experts say the best ways to avoid getting the flu include washing your hands frequently and getting a flu shot.
This year's vaccine offers protection from the H1N1 virus.
"We worry about flu in anyone who has chronic illness, asthma, in pregnant women, in the elderly, in young children, but this one, we worry about people who don't fall into those groups," ABC News Chief and Medical Editor Richard Besser said.
Last week, Santa Clara County reported California's first flu death of the winter season.
That person tested positive for H1N1.
The swine flu has also been found in Contra Costa and Marin Counties.