DENVER - Officials with the Colorado Department of Health noticed a large spike in flu cases in October. The number of hospitalizations has been growing ever since.

Normally about seven or eight people are hospitalized for influenza at this time of year. Currently, the number is 52 hospitalizations, state health officials say.

"This is a big deal," said state epidemiologist Lisa Miller.

Yet for the moment, Miller isn't sure why it's happening.

 "It may be an obvious question. It's a really hard question. And it's a question we really can't answer," said Miller.

So doctors in Colorado and at the Centers For Disease Control and Prevention in Atlanta are reviewing specific cases, trying to find a trend.  But  they do know people are getting shots and feel the vaccine is a good match.