Patients have been flooding emergency rooms across the country, as an early and fierce outbreak of the flu hits 41 states.
More than 2,200 people are in the hospital and staff are taking extra precautions. One hospital in Minnesota has even banned visitors.
Doctors across the nation say they're overwhelmed.
"It's epidemic," says Dr. David Rosenberg, a pediatric pulmonologist. "It's been huge and there's been a lot of admissions for flu more than ever."
Doctors in Illinois say they haven't seen this many cases since the swine flu outbreak in 2009.
18 children have died in the U.S. The Center for Disease Control (CDC) says 18 states are reaching epidemic levels.