The illness is also causing a low blood supply at Mercy Hospital St. Louis.
"This time of the year we can see with the influenza season where a lot more patients are affected," said Dr. John Finnie, who workers in the hospital's cancer care unit.
"It's a time where we don't see perhaps as many people coming in who are helping with blood donations, so that's the one thing we want to get out there," he said. "It's a level-one trauma center in a really busy facility, so it's a nice opportunity where people want to come in help out."
The hospital, like several others across the area, is opening up extra rooms to treat the sick.
"We have been so busy," said Christina Bunton, who is a registered nurse with the hospital.
"We have opened up areas just in the emergency room," she said. "We opened up hall spots, we put patients in every available spot where we can put them."
SSM Health St. Clare Hospital is also experiencing an increase in the number of patients with the flu and has temporarily expanded its emergency room to accommodate.
According to the Centers for Disease Control, more than 40,000 cases of the flu have been reported in the state and this year the illness has caused more than 600 deaths.
Bunton said that while the hospital won't turn anyone away, not everyone with the flu has to make a trip to the emergency room.
"If you're managing fluids, if your medication is responsive and if you're not having any respiratory stress, if you're not becoming dehydrated then there's really not a need to put yourself out there or expose others," she said.
Doctors said it's not too late to get your flu shot but check with your physician first.
If you would like to donate blood, call ahead or visit MercyBloodDonor.net.