CHICAGO (AP) — Hundreds of children in about a dozen states have been sickened by a severe respiratory illness that public health officials suspect may be caused by an uncommon virus similar to the germ that causes the common cold.

Nearly 500 children have been treated at one hospital alone — Children's Mercy in Kansas City, Missouri — and some required intensive care, according to authorities.

The suspected germ, enterovirus 68, is an uncommon strain of a very common family of viruses that typically hit from summertime through the fall.

The virus can cause mild coldlike symptoms but this summer's cases are unusually severe, said Mark Pallansch, director of the viral diseases division at the federal Centers for Disease Control and Prevention.

"It's not highly unusual but we're trying to understand what happened this year in terms of these noticeable and much larger clusters of severe respiratory disease," Pallansch said Monday.

The virus typically causes illness lasting about a week and most children recover with no lasting problems.

Authorities in Illinois and Colorado said their states are among those with suspected or confirmed cases.

Children with asthma and other health problems are especially at risk, but reported cases include children without asthma who have developed asthmalike breathing problems, Pallansch said. He said no deaths have been reported in the outbreak.

Dr. Mary Anne Jackson, director of infectious diseases at Children's Mercy, said local cases began appearing in mid-August and they appear to have peaked in her area.