(ATLANTA) -- The flu continues its steady spread across the U.S. during a frigid winter, with the virus widespread in 35 states, up from 25 last week, according to the U.S. Centers for Disease Control. This flu season has been particularly hard on adults between the ages of 18-64, often thought of as young enough to fend off the worst flu symptoms. This season 61.5 percent of hospitalized flu patients are between the ages of 18 and 64. It's a sharp increase from last season when they made up 34 percent of hospitalized flu patients.
Of the 2,486 specimens that tested positive for the flu from the U.S. World Health Organization and the National Respiratory and Enteric Virus Surveillance System, 96 percent tested positive for H1N1, commonly known as the swine flu. Although the flu shot offers some protection against H1N1, it will not fully vaccinate against the virus.
Two high profile deaths have drawn attention to the risks for younger adults and the flu. Last week a 29-year-old mother of three died after just a few days of experiencing flu like symptoms. Another 41-year-old man also died.
ABC News Chief Health and Medical Editor Dr. Richard Besser said the flu isn't only dangerous for the very old or the very young.
"It's very hard to predict who is going to have a bad case of the flu, usually it's the young or elderly," said Besser, who said it's unclear why some people are more susceptible. "You have to ask why people in this age group. There's a couple possibilities, healthy young adults in the past have been less likely to get the flu vaccine."
Besser points out that in recent years the vaccine has helped protect people from being infected with the H1N1 virus.
Approximately 9.7 out of every 100,000 people with the flu have needed to be hospitalized according to the CDC.
Although the country has not quite reached the epidemic level, the number of states experiencing widespread geographic influenza, which refers to the spread of flu, rose to 35, up from 25 last week.
The CDC also reported an additional four pediatric deaths bringing that total to 10. However, some of the four reported deaths happened earlier than last week but were only recently reported.
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