A mysterious carbon monoxide leak at a Pennsylvania daycare sent dozens of children and staff to hospitals Tuesday morning, Allentown officials said.Some of the 19 patients treated by the Lehigh Valley Health Network had been discharged by Tuesday afternoon, but some had high carbon monoxide levels that “required more aggressive treatment,” and were transferred to Hospital of the University of Pennsylvania and Children’s Hospital of Philadelphia, Andrew Miller, the head of pediatric Emergency Medicine at the network, said in a statement.As of late Tuesday morning, firefighters were still at the daycare trying to “mitigate the problem and ventilate the structure,” Ortega said.Carbon monoxide can come from a variety of sources, such as gas stoves, generators and other gasoline-powered equipment, car exhaust, gas space heaters, fireplaces and gas water heaters, according to the U.S. Environmental Protection Agency.“It is important to provide quick treatment to replace the CO in the blood with oxygen as excessive inhalation of CO is associated with acute and long-term consequences, including damage to the brain and heart, which require a lot of oxygen,” Miller said."