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The rare respiratory illness affecting children has now been confirmed in a dozen states, the Centers for Disease Control and Prevention reported Tuesday.

The two newest states with confirmed cases: Oklahoma and Pennsylvania, which join a growing roster of states that officially have cases of enterovirus 68, a rare virus strain that can cause severe breathing problems.

Hospitals around the country are seeing an increase in the number of children dealing with respiratory illnesses. Testing has shown that many of these children are suffering from this enterovirus strain. Enteroviruses are quite common, causing between 10 million and 15 million infections each year, but this particular strain has not appeared very often since it was first isolated in California in 1962.

So far, the other states with confirmed cases are Alabama, Colorado, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Missouri and New York. There have been 130 confirmed cases, the CDC says, but the number of actual cases is likely much higher.

Public health officials continue to warn that other states are presumably going to join this list, with cases expected to be confirmed in other places where there have been clusters of children suffering from respiratory illnesses.

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