DENVER -- Colorado's flu outbreak is growing, with cases cropping up in the western half of the state for the first time.

The flu has hit hard at schools, forcing some to shut down altogether: Officials in Fairplay gave 530 students in three schools Thursday off after about a third of them didn't show up for class a day earlier.

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"Schools and preschools are pretty good places to pass all respiratory illnesses because you have a lot of people put together in one place," said Ned Calonge, the state's chief medical officer.

Officials say 1,525 flu cases had been reported statewide as of Wednesday, up from less than 300 at the end of last week. There were only 2,681 cases all of last season.

Texas is the only state experiencing a "widespread" outbreak of flu, the Centers for Disease Control and Prevention said. Colorado health officials will ask the CDC to upgrade Colorado's outbreak from "regional" to "widespread" by Friday -- the highest level of activity.

"We will meet the criteria, I can say," said Dr. Ken Gershman, head of the state health department's communicable-disease program.

So far, no one in Colorado has died of the flu, which kills an estimated 36,000 people across the nation every year.

Colorado's Front Range is bearing the brunt of the cases so far, but cases are being reported in Eagle, Garfield and Pitkin counties.

"We're seeing more cases earlier," said public health nurse Laurel Little of Garfield County Nursing. "Because of these early cases, we'll likely see that peak much earlier this winter."

Thousands of people are seeking flu shots. The CDC said this year's dominant flu strain doesn't match up with the vaccine, but urged people to get the shots anyway.

Statewide, this year could be a "record-breaker" in terms of number of cases, Gershman said. He points out that the flu, which generally runs from November to March, struck earlier than usual.

One of the victims, 9-year-old Nathan Puente, said the flu hit Sunday. He vomited while visiting his father at work.

"It wasn't that good of a feeling. I can tell you that much," he said. "I sure don't want to go through that again."

To get more information on the flu and its symptoms, you can call the Colorado flu hotline from 7 a.m. to 11 p.m. at (877) 462-2911. To find out where there's a flu shot clinic near you, call (888) 692-0269.