Recent research from CU Boulder may have finally revealed why humans tend to get sick from airborne viral diseases more often in drier environments.
Published in December in PNAS-Nexus, the study found that airborne particles carrying a mammalian coronavirus closely related to the virus which causes COVID-19 remain infectious for twice as long in drier air, in part because the saliva emitted with them serves as a protective barrier around the virus, especially at low humidity levels.
The study carries major implications for not only the current COVID-19 pandemic but potentially for all infectious diseases transmitted by saliva-coated viruses. The research also further emphasizes the importance of managing indoor air filtration and ventilation to mitigate airborne disease spread, especially for buildings in arid states such as Colorado, dry enclosed environments such as airplane cabins and during dry winter months in temperate climates worldwide.
"The physics of the air in our buildings and the climate in which we live affect things that can make us sick and how long they persist. Now we have conservative indications of how long coronaviruses like the one that causes COVID-19 can stick around in the air and be an infectious disease threat," said Mark Hernandez, senior author and S. J. Archuleta Professor of Civil and Environmental Engineering.
In 2020, Hernandez had a hunch that both relative humidity and saliva were important factors in the transmission of the novel virus sweeping the globe. He also happened to run the Environmental Engineering Microbiology and Disinfection Lab, one of the country's only full-scale bioaerosol labs ready and able to take on the challenge at the start of the pandemic.
Professor Mark Hernandez and doctoral graduate Marina Nieto-Caballero stand inside a bioaerosol chamber in the Environmental Engineering disinfection laboratory at the Sustainability, Energy and Environment Complex (SEEC). Photo by Patrick Campbell/CU Boulder.
Civil engineers design and operate buildings in the U.S. to maintain an indoor relative humidity between about 40% and 60%. In the real world, however, these percentages vary more widely. In San Francisco for example, where Hernandez grew up, the relative humidity pushes a dewy 60%. In comparison, Colorado hovers at an arid 25%.
