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KANSAS CITY, Mo. (WDAF) – An unusual respiratory virus is affecting kids in the Missouri area by the hundreds.

Children’s Mercy Hospital is hospitalizing 20 to 30 kids a day with the virus that causes severe breathing trouble.

So far, the hospital has seen more than 300 cases in recent days in kids of all ages.

Preston Sheldon’s mother says he seemed fine when she took him to pre-school on Tuesday.

Minutes later, she got a call that her 3-year-old son was having trouble breathing.

“You could see his ribs and his stomach was pushing out really hard. I thought it was an asthma attack,” said Pam Sheldon.

However, it was actually enterovirus 68, which is inundating Children’s Hospital with patients.

“To be at winter census is quite unusual in August, obviously. To see a virus we’ve not seen before is unusual too,” said Dr. Mary Anne. Jackson, an infectious disease specialist.

Enterovirus 68 is well-known around the world but is relatively rare in the central United States, until now.

“We have about 10 to 15 percent who have severe illness from this virus, which actually acts like asthma exacerbations,” said Dr. Jackson.

Experts say about two-thirds of those hospitalized are children with a history of asthma or wheezing.

However, the virus will produce an ordinary cold in many healthy children as well.

“The difficulty breathing is a very obvious tip-off sign they need to come into the hospital,” said Jackson.

Children’s Mercy has posted signs, warning parents that children under the age of 12 should not visit patients.

There is no anti-viral medication for enterovirus 68 and no vaccine.

However, many patients require supportive care, like oxygen.

Preston’s mother says she is glad they didn’t wait to go to the emergency room.

“Cause it can hit really fast. And without medical treatment, it could get really bad,” she said.

Experts say enterovirus 68 can range in severity.

Medscape says the virus is associated with respiratory illnesses that are relatively mild to severe cases, which require patients to be in intensive care.

Three cases were actually fatal; two in the Philippines and one in Japan.