What's All This Buzz About Humidity and preventing infections...

I came across an interesting article recently, thanks to my alert friend Leisa. The title of the article was “Is low indoor humidity a driver for healthcare-associated infections?” written by Stephanie Taylor, MD, M Arch from Harvard Medical School and reviewed in Forbes Magazine by Leah Binder. (October 17, 2019). I was interested because it sounded like maybe there was a non-pharmaceutical method that might prevent influenza like illnesses and hospital infections and I’m all for that! Dr. Taylor reminded me of a modern day medical detective in the way she investigated this question. As a scientist, when we see something that doesn’t make sense, we ask ourselves why? What are the factors contributing to the increased incidence of infection in hospitals? Ineffective hand washing? Room cleaning procedures? Contamination in the ventilation system? She did an extensive evaluation of a hospital building and looked at millions of data points and concluded that DRY AIR was a big contributor that had not been previously considered or studied. Dry air!! Why would that be?

If you are a germaphobe, you might want to stop reading now. The truth is, there are microbes everywhere around us. Every time we breathe, bacteria and viruses from our mouths are expelled into the air around us. When the air is dry, the droplets that carry microbes are small, travel further through the air, are able to penetrate more deeply into our respiratory tract and are more virulent. With increase in the relative humidity(RH) of the room, the droplets become bigger and heavier and fall to the ground more quickly. There are also microbes in the air from skin flakes that become airborne, especially with dry air. When Dr. Taylor’s team looked at the data, there was a significant decrease in the rate of infections that correlated strongly with relative humidity in the 40% to 60% range. So during the colder, dryer winter months when the RH was below 40%, the incidence of healthcare infections increased. This included influenza as well as other hospital acquired infections. Not only are microbes more virulent in rooms with lower RH, our bodies are more susceptible to infection when our nasal mucosa and respiratory mucosa are dry from the lower RH. More research is needed to sort out what the mechanisms are for this increased incidence of infection, but the indication is that the RH plays a significant role.

Another study done by the Mayo Clinic had similar findings. (PLoS One 2018 Sept 25:13(9) Humidity as a non-pharmaceutical intervention for influenza A) In this study they used a preschool setting in the community and had one classroom that was humidified to an absolute humidity (AH) of 9.86mb compared to a control classroom with an AH of 6.33mb. (There is a difference in RH compared to AH that I had to look up to understand, but basically one room was humidified and the other wasn’t) From Jan25-March 11, 2016 10 influenza-like illnesses (ILI) from absent students were recorded by school personnel. Seven were from the control room, three were from humidified room. Both sets of rooms had the same number of absences due to illness overall, but there were more ILI in the control classroom.

The study monitored the presence, genomic copy number and infectivity of influenza A virus in the preschool classrooms during the dry winter months. This correlated with peak respiratory virus infections in Minnesota. Increasing AH from 6.33mb in the control room to 9.89mb in the humidified room was associated with a significant decrease in Influenza A virus presence in fomite and air samples in the humidified room compared to the control room. And virus positive samples from the humidified room had lower infectivity than samples from the control room.

Fomite is a funny word that means an object (such as a cup or a doorknob) that may be contaminated with infectious organisms such as viruses or bacteria, and allow their spread. You can imagine all the potential fomites in a preschool classroom-light switches, toys, tables, used kleenexes etc. And don’t forget cell phones, computer keyboards, and remote controls in other settings. Viruses have been shown to live and remain infective for several days on bank notes! Your Mother was right! Money is dirty stuff! Wash your hands please.

Now that you know about relative humidity and prevention of infections, what do you do next? I ordered a hygrometer from Amazon to see what the RH was at my daughter’s house where I am visiting. It was 52%-phew! No dry air for me. But it isn’t winter yet, so I will keep monitoring. I remember winters in Virginia when the inside RH was below 20%! Should you get yourself a personal humidifier to carry with you to school or work? Talk your kids preschool into humidifying the classroom? I plan on finding a good humidifier for the winter and see if it keeps the household healthier. Looks like more research is in order!

Unrelated fun fact: Fear of Halloween is called Samhainophobia.

And another one I never heard of: Fear of long words: Hippopotomonstrosesquippedaliophobia. I seriously did not make this up!

For more information on the work that Dr. Taylor is doing, there is a Youtube video called “Better Health is Just a Breath Away”, as well of many other studies relating the effects of humidity on incidence of infections.