A respiratory virus has stricken more than 1,000 children across 12 states, causing many to wind up in the hospital and causing doctors to sound the alarm that this will probably become a nationwide epidemic.

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.

Doctors expect the number of places and people affected to increase, too.

"Viruses don't tend to respect borders," ABC News Chief Health and Medical Editor Dr. Richard Besser said. "It is only 10 states now, but it's going to be across the country. So if your state doesn't have it now, watch for it, it's coming."

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.

Public health officials from many of these states have requested assistance from the CDC, according to Pallansch, and many fear the beginning of the new school year could allow the virus to gain momentum. Although the illness associated with the infection typically lasts about a week with cold-like symptoms, all children who have had the sickness so far have recovered completely, health officials said.

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 U.S. 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.

Children infected with this virus will appear to have a severe cold, with runny nose, sneezing and cough, according to Children's Hospital Colorado. But the illness can escalate quickly in some cases, and the child may start to have trouble breathing.

Doctors advise that if a child has a cold, and then starts wheezing or struggling to breath in any way, seek medical health immediately.

Doctors advise paying special attention to children who already have breathing issues like asthma. Without proper treatment, the sickness could be deadly in some cases.

Missouri, Colorado, Georgia, Illinois, Iowa, Kansas, Kentucky, North Carolina, Ohio and Oklahoma have sent samples to the CDC for analysis, according to news reports.