Hospitals across the Denver metro area are on alert for a mystery respiratory illness that can leave children and teenagers with asthma debilitated. Doctors told 7NEWS they believe the illness is linked to human enterovirus 68, which is related to rhinovirus, which is a cause of the common cold. Patients often complain of a rapid onset of cold-like symptoms and then suddenly are unable to breathe. "My head started hurting and after that my lungs started sort of closing up. It felt different," said 13-year-old Will Cornejo, of Lone Tree. "He was in really bad shape. He came really close to death. He was unconscious at our house and white as a ghost with blue lips -- he just passed out," said Will's mother, Jennifer Cornejo. "To go from a cold to you know, minutes away from death is kind of scary," said his mother, Matt Cornejo. At Rocky Mountain Hospital for Children, physicians report about 10 of the 20 beds in their pediatric intensive care unit are young people battling the virus. "Our pediatric floor is full of patients with pretty severe respiratory distress," said Dr.Raju Meyappan, a critical care physician at Rocky Mountain Hospital for Children. Officials at Children's Hospital Colorado say they are also experiencing a surge in patients fighting the same virus -- up to 250 children a day since Wednesday. Doctors say the virus is extremely rare and they have yet to pinpoint when it first appeared in the Denver metro area, and why so many cases have sprung up recently. Since Aug. 18, more than 900 children have been treated for severe respiratory illness at Children’s Hospital Colorado emergency and urgent care locations in metro Denver; of these, 86 have been admitted into the hospital. Children’s Hospital officials said they started their usual wintertime visitation policy early this year due to the increase of respiratory viruses circulating since mid- to late-August. Because viruses cannot be treated with antibiotics, doctors said prevention is the best medicine.