Last Updated Sep 8, 2014 11:05 AM EDT
Hundreds of young children suffering from a for a respiratory illness that has symptoms similar to a common cold have been filling up intensive care units in several Midwest cities.
As the school year gets underway, a CDC official said in an interview Sunday that the large number of seriously ill patients being reported now could be "just the tip of the iceberg in terms of severe cases."
"We're in the middle of looking into this," Mark Pallansch told CNN. "We don't have all the answers yet."
Human enterovirus 68 is related to the common cold but within hours those affected can become severely ill.
"It is a rare strain of a very common virus," CBS News medical contributor Dr. Holly Phillips told "CBS This Morning." "The most important thing to pick up on is any difficulty breathing. Wheezing or a cough that just won't stop, those are the warning signs and parents should have a low threshold for heading to the hospital with that."
While it tends to affect sufferers of diseases like asthma worse, many parents have been left surprised that within just hours of relatively benign symptoms their children are left gasping for air and placed on a ventilator in the ICU.
Apparent sufferers of the illness are filling up intensive care units at hospitals around Colorado, CBS Denver reports.
Children's Mercy Hospital in Kansas City had reported treated about 450 cases in young children as of early last week.
More than 70 children complaining of respiratory virus symptoms visited the Blessing Hospital in Quincy, southwest Illinois, during the Labor Day weekend, according to Reuters.
St. Louis hospitals have also issued warnings about the disease's outbreak.
Hannibal Regional Hospital near the Missouri-Illinois border asked on its Facebook page "that children 16 and under and persons with the following symptoms refrain from visiting patients who are hospitalized at Hannibal Regional Hospital until further notice," due to the virus.
"I remember thinking I was going to die," said 13-year-old Colorado resident Will Cornejo. "Yesterday I felt like I couldn't breathe at all."
Will had to be placed on oxygen after visiting a Denver hospital.
"He was white as a ghost, his lips were blue, he was completely unconscious at that point," said Will's mother, Jennifer Cornejo.
His father, Matt Cornejo, said they felt "sheer terror."
In the ICU at Rocky Mountain Hospital for Children, Dr. Raju Meyappan said the virus hadn't shown up in Denver until now.
Now he is seeing how quickly this virus becomes life-threatening, especially in children with mild asthma.
"The onset of symptoms was very rapid, usually within hours," said Meyappan.
Since human enterovirus 68 is a virus, antibiotics don't work. Doctors can only treat the symptoms, helping kids breathe and trying to keep their airways open.