“Try and know your body, don't let things go. You know whenever you have a fever, and you have it multiple days, just don't let it go. Get it taken care of,” Todd Baughman said tearfully.

He never imagined he'd lose his active, seemingly healthy son, Kyler, to complications from the flu.

“We noticed he wasn't feeling well. Looked like he was run down,” Kyler's mother Beverly Baughman explained.

When they saw Kyler on Christmas he had a runny nose. He was also coughing and complaining of chest pain.

The 21-year-old aspiring personal trainer died just a few days later in Pennsylvania. The cause was organ failure due to septic shock caused by influenza.

More than a thousand miles away in Texas, 37-year-old Nita Negrete tested positive for the flu that quickly turned to pneumonia. The mother of three also passed away.

“It doesn't seem real. We're just waiting for her to walk in the door. She was just so young,” said Jazmyn Garza, Negrete's niece.

So how do you know it's time to seek medical attention? Doctors say it's not uncommon to experience a fever with the flu for as long as a week.

However you should be on the lookout for prolonged high fevers associated with bad headaches, coughing up fluids, and overall feeling terrible.

So far this season, more than 40,000 cases of the flu have been reported. That's three times as many as the same period last year.

It's never too late to get a flu shot. Those who have been hit the hardest are warning everyone take the virus seriously.

“I just think he ignored it and thought, 'oh, it will go away' like most people. And I think people need to pay more attention to their bodies,” Beverly Baughman said.

Doctors said usually people who do poorly with the flu have other medical issues with heart, lungs, kidneys, etc.

But with any illness, it's somewhat a case by case basis.