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NEW YORK (CBSMiami) – Researchers have found that the deadly flu virus spreads more easily than previously thought.

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At least 240 schools across the country are closed Thursday to stop the virus from spreading. At one Wisconsin school, 30 percent of the students were absent this week because of the epidemic.

There have been more than 4,500 flu-related deaths this season, of those at least 53 were children.

Most parents know they need to closely monitor children under 5 for any signs that their symptoms are getting more severe. It’s important to pay even closer attention to babies and toddlers under 2, making sure they are getting enough liquids because they can easily become dehydrated.

The following symptoms in children with the flu call for immediate medical care, according to the Centers for Disease Control.

  • Fast breathing or trouble breathing
  • Bluish skin color
  • Not drinking enough fluids
  • Not waking up or not interacting
  • Being so irritable that the child does not want to be held
  • Flu-like symptoms improve but then return with fever and worse cough
  • Fever with a rash

To get a better handle on how the flu spreads, University of Maryland professor Dr. Donald Milton came up with a machine he’s dubbed the Gesundheit II.

“It just is pulling all of the air from around your face at a fast enough rate that we collect everything but not so fast that it feels like there’s a breeze,” said Milton explaining how it works.

Milton is using the device to collect and analyze the flu virus in an exhaled breath. With those virus samples, researchers are trying to track down how the flu spreads.

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“The focus has always been on telling people that coughing and sneezing are how it’s transmitted,” said Milton.

In 2014, MIT used high-speed imaging to study just how far cough and sneeze droplets, and therefore germs, can spread.

But earlier this year, a Centers for Disease Control study found that the flu virus can be transmitted simply by breathing.

“If we understand better how much of the infection is transmitted by air and what the dose in the air is, we can then figure out how to reduce your exposure,” said Milton.

Milton and his team are using student volunteers to study the mechanics of how the bug spreads by swabbing people who have come in contact with infected students.

If I can show that you got the flu from him and it didn’t come from his nose but it came from his lung then you’ve got it by the airborne root. We got the answer,” said Milton.

This year’s nasty flu season means workers are staying home and it’s costing employers a bundle.

Businesses can expect to take a hit of at least $15.4 billion in lost productivity due to this year’s flu season, according to a study released by outplacement firm Challenger, Gray & Christmas Inc.

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The CDC predicts that 18 million employed adults will miss four workdays due to the flu.