Humidification and Virus

The Environmental Health Journal published an article this past month titled, "Modeling the airborne survival of influenza virus in a residential setting: the impacts of home humidification".  The results of the research taken from the article are, "The presence of a portable humidifier with an output of 0.16 kg water per hour in the bedroom resulted in an increase in median sleeping hours AH/RH levels of 11 to 19% compared to periods without a humidifier present. The associated percent decrease in influenza virus survival was 17.5 - 31.6%. Distribution of water vapor through a residence was estimated to yield 3 to 12% increases in AH/RH and 7.8-13.9% reductions in influenza virus survival." 

What the article states that a slight rise in relative humidity in the room caused a slight drop in the influenza viruses in the air.  I have a couple of criticisms about the article, though.  The authors derived this conclusion based on limited data using modeling instead of actual sampling of the virus.  The lack of data does not really show how the trend would go for humidity versus virus concentrations.  Without data from actual virus, the question also exists whether the model is realistic or whether the results are repeatable.  I cannot really fault them because sampling for viruses is difficult at its least, particularly infectious viruses and research is expensive.

But, I am still concerned about whether the risks of a humidification system are worth the beneficial effect on virus.  Other studies have shown that hygiene--hand washing and avoiding sick people--are quite effective in preventing or minimizing virus-related illnesses.  Flu shots are also effective in preventing flu for which the sera are developed.  I can personally attest to that fact.  I also tend to believe that flu shots, even past ones, may help minimize the effects of other virus.

I will confess, though, that I am not a big fan of some humidification systems, particularly central humidification systems.  I have observed too many issues with them from basic design to maintenance-related issues.  In future blogs, I am going to go into more detail about humidification systems and their pros and cons, as I see them.  I even got off on that tangent writing about those issues for this blog.  I decided to reign in this post to stick with the topic of humidity and virus.

What can be drawn from this and other research.  I believe that humidity levels could have an effect on virus levels in the air.  I have known for a long time that when those sloppy wet infectious particles that are sneezed into the air, or fomites as the medical gang call them, they have a better chance of drying in low-humidity air.  Drying of the particles means that they become smaller and lighter, which in turn means that they can stay afloat in the air longer.  They can also be breathed deeper into the respiratory system where they can more easily set up shop.  The weird thing is that some virus actually survive better in the dried out state.   (Here are a couple of examples of research pointing to that conclusion:  "Dry air might boost flu transmission" and "Flu Mystery Solved? Why It Flourishes in Winter".)  Elevated humidity is a good thing.  My dispute is with the way to humidify, and that will be the subject of other posts.