Widespread Flu Reported in 25 States: CDC

Flu season is getting into high gear across the US, the Centers for Disease Control and Prevention confirmed Friday, with a report that half of the country is reporting widespread seasonal flu activity.

During the final week of 2013, widespread flu activity had jumped from 10 states the week prior to 25, according to the CDC's Weekly Influenza Surveillance Report.

Widespread flu activity was reported in Alabama, Alaska, Arkansas, Colorado, Connecticut, Georgia, Idaho, Illinois, Indiana, Kansas, Louisiana, Massachusetts, Minnesota, Nebraska, Nevada, New York, North Carolina, Oklahoma, Oregon, Pennsylvania, Texas, Utah, Virginia, Washington, and Wyoming.

The CDC considered flu to be "widespread" in a state when more than 50 percent of its geographic area is reporting flu activity. The widespread classification does not relate to the severity of the flu strain.

The CDC report also indicated a high level of doctor visits by people with "influenza-like illnesses" in 20 states, the majority of which are in the South and Midwest. This high activity level is based on the number of outpatient visits to health care centers for flu-like illnesses. The CDC notes that a high level of activity in a state is not necessarily correlated with a geographically widespread flu outbreak. "Outbreaks occurring in a single city could cause the state to display high activity levels," the CDC said, of the map below. 

The most common strain of flu so far this year is H1N1, which became known as swine flu during a 2009 outbreak.

"It's the same virus that we saw in 2009 that caused the pandemic," said Michael Jhung, a medical officer in the CDC's flu division, who spoke with CNN.

The first time H1N1 was seen in humans was 2009, which is why it became known as swine flu. But in the years since, "it's established itself very nicely in the human population," Jhung said. "We've seen it every season since 2009 in people." H1N1 is no longer referred to as swine flu, but instead as a human seasonal virus, CNN reported.

This time of year, flu activity is traditionally high in North America. In a collaboration with Google, the CDC and the data company have created a world map that tracks flu activity based on aggregated Google search data.

As of Saturday (Jan. 4) morning, the Google Flu Trends map indicated a "high" level of flu activity in all of North America and Spain. The map indicated flu activity to be "moderate" throughout most of Europe and "minimal" in most of South America, Australia and South Africa.