Virus hitting Midwest may be 'tip of iceberg'

(CNN) -- A respiratory virus is sending hundreds of children to hospitals throughout the Midwest and beyond, health officials say.

The unusually high number of hospitalizations reported could be "just the tip of the iceberg in terms of severe cases," said Mark Pallansch, a virologist and director of the Centers for Disease Control and Prevention's Division of Viral Diseases.

Twelve states have contacted the CDC for assistance in investigating clusters of enterovirus: Alabama, Colorado, Michigan, Georgia, Ohio, Iowa, Illinois, Missouri, Kansas, Oklahoma, Kentucky and Utah. Four -- Colorado, Illinois, Missouri and Iowa -- have confirmed cases of Enterovirus D68, also known as EV-D68.

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