Can humidity help prevent spread of flu virus?

Tyler Koep
Mayo Clinic pre-doctoral candidate Tyler Koep, 24, holds a humidity sensor at Lincoln K-8 Choice School in Rochester on Thursday, Jan. 10, 2013. There are 30 of these little square sensors all around the school. For the last two years, Koep has used them to track the temperature and humidity levels inside the building. He's trying to determine if raising the humidity level inside the school during the dry winter months could decrease the flu's survival rate and transmission.
MPR Photo/Elizabeth Baier

A Mayo Clinic researcher is testing the theory that controlling indoor humidity levels can help control the influenza virus in transmission hotspots like schools, hospitals, daycare centers and churches.

The virus can spread quickly in those areas, especially in the winter time when low humidity levels help the influenza virus survive longer outside the human body.

At Lincoln K-8 Choice School in Rochester, Tyler Koep has placed 30 little square sensors all around the building. For the last two years, he's used them to track the temperature and humidity levels.

Koep is trying to determine if raising the humidity level inside the school during the dry winter months could decrease the flu's survival rate and transmission. And he's using standard store-bought humidifiers to raise those levels.

"How many humidifiers would it take to bring up the level of the whole school? Koep asked. "We know a room at a time is possible, but would a room and an adjacent room be possible? That's something we're not quite sure of."

Koep, 24, is a pre-doctoral candidate at Mayo Clinic's graduate school. Last year, when he raised the humidity level of a single classroom from roughly 15 to 60 percent, Koep projected the virus's survival rate would drop from 70 to 30 percent in one hour.

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Now, he wants to try to do that for the entire building by placing 25 humidifiers around the school. Mayo Clinic is funding his research with several grants, totaling $15,000.

Humidity monitor
Mayo Clinic pre-doctoral candidate Tyler Koep has placed 30 humidity sensors all around Lincoln K-8 Choice School in Rochester.
MPR Photo/Elizabeth Baier

"If these early humidity experiments continue to prove successful and follow our hypothesis, we'll go back and we'll actually do a trial where students are present, humidifiers are going either as part of our own humidification or school humidification, and then over time we can measure absenteeism rates, or reports of influenza-like illness and hopefully see those numbers go down," Koep said.

Koep doesn't yet have numbers that correlate the increased humidity with lower levels of flu in students and staff. He believes his early humidity experiments could represent practical, real-world solution to minimizing the flu at hotspots around the a community.


But adjusting atmospheric humidity levels is a tricky business because too much humidity is not a good thing.

Absolute humidity is the actual amount of water content in the air, regardless of temperature. Relative humidity is expressed as a percent and measures the current absolute humidity relative to the air pressure and temperature.

Jeffrey Shaman, an atmospheric scientist at Columbia University in New York and the lead author of a 2007 study that identified the link between influenza and absolute humidity, is working with Koep on his research with humidifiers.

"If you overly humidify a building you're going to get things like building rot in areas, you're going to get the build up of mold, some of which could be pathogenic," Shaman said. "Those are some of the adverse affects that you wouldn't want to engender through any of your efforts."

Shaman said it's hard to tell whether Koep's theory will just forestall the inevitable flow of the virus through the school, or if it can effectively slow an outbreak.

"But, if it worked really well, and that's a big if, then perhaps it would slow the outbreak a bit," Shaman said. "It might give the community a little extra time to go out and get vaccinated, perhaps a little more time to protect itself in other ways and deal with the outbreak as it's unfolding."


Teachers and school administrators are hopeful that lowering the lifespan of the flu could translate into fewer students passing the virus along to each other.

Corey Dornak, a science teacher at Lincoln, said that would be "huge."

"It'd be less kids hopefully absent, which would make my job easier," Dornak said.

Only a handful of students have come down with the flu at the school so far this year. But statewide, five schools had outbreaks of influenza-like illness last week.

And Dornak said once there's an outbreak, school officials have a hard time stopping the virus from spreading.

"It's hard to get kids caught up and when they miss school, obviously, even if you try to catch them up, they can never really replace, they never get the same lesson," Dornak said. "If we can figure out a way to control the humidity levels so that they're not getting sick, it's going to be beneficial to everyone."

Koep is still years away from determining conclusively whether his theory is correct.

But if future flu seasons are anything like this one, his research may prove to be useful in years to come.