A respiratory virus has stricken more than 1,000 children across 12 states, causing many to wind up in the hospital and prompting concerns of a wider outbreak.

The CDC has identified the culprit as a rare respiratory virus known as Enterovirus D68, or EV-D68, that’s part of the family of viruses that includes the common cold.

EV-D68 is largely responsible for two clusters of respiratory illness in Kansas City, Mo, and Chicago, Assistant Surgeon General Dr Anne Schuchat, director of the US National Center for Immunization and Respiratory Diseases, said during a Monday news conference.

A CDC lab found that 19 of 22 specimens from Kansas City and 11 of 14 samples from Chicago tested positive for EV-D68, Schuchat said. The virus has targeted children, infecting kids from 6 weeks to 16 years old, she said.

About 15 percent of more than 300 children treated for respiratory illness in Missouri have ended up in an intensive care unit, according to a health alert from the Missouri Department of Health and Senior Services.

Children’s Hospital Colorado reports that 86 kids have been hospitalized out of more than 900 treated for severe respiratory illness since Aug. 18.

The number of hospitalizations reported so far could be “just the tip of the iceberg in terms of severe cases,” Mark Pallansch, director of the U.S. Centers for Disease Control and Prevention’s Division of Viral Diseases, told CNN.

The CDC is asking doctors and public health officials to consider EV-D68 a potential suspect if widespread respiratory illnesses start occurring in their communities, she said.