One of the worst flu seasons in a decade is putting further strains on an already sluggish U.S. economy as companies get slammed with increased health care costs and lower productivity from widespread worker absences.

On average, seasonal flu outbreaks cost U.S. employers $10.4 billion in direct costs of hospitalization and outpatient visits, according to the Centers for Disease Control. That doesn't include the indirect costs related to lost productivity and worker absenteeism.

But this year, that figure is expected to go much higher, as the flu virus has shown up in some 41 states with 29 of them reporting high or severe levels of sickness as thousands are flooding into hospital emergency rooms and doctor's offices.

"If this is a major influenza outbreak, like the Spanish flu of 1918, it could have a very significant effect on economic growth," said Timothy G. Nash professor in Free Market Economics at Northwood University. "If GDP is projected to be be 2 percent this year, the flu could cut that back to one half percent growth rate." (Read more: Vaccine Shortages Reported)

"A non-epidemic flu costs the U.S.economy with roughly 36,000 lives and causes more than 200,000 people to be hospitalized and costs our economy," Nash said. "We don't know if this is a like 1918 but we can't ignore the serious nature of what's going on."



"The last thing we need in a slow economy is a major flu epidemic," said Paul Mangiamele, CEO of the Bennigan's restaurant chain located throughout the U.S. "It's bad enough as it is without the flu taking even more customers away."

Mangiamele said his company is on "orange alert' to try and keep the flu impact to a minimum.

"We have basic high-end standards on hygiene any way but we're doing more work in making sure our utensils are extra clean and making sure the salt and pepper shakers have been rubbed down and every worker washes their hands. We're just ramping up our normal effort," said Mangiamele.