CU researchers find airborne viral diseases survive longer in dry climates like Colorado’s

Colorado’s dry climate is ideal for airborne viruses to survive, according to a new study published in PNAS Nexus by researchers at the University of Colorado Boulder, potentially explaining why people who live in dry climates are more susceptible to such infections.

This study, which incorporated a live coronavirus that does not cause COVID-19 rather than bacteria or fungi, showed that airborne viral particles in artificial saliva remain infectious for nearly twice as long in a drier climate than in a humid one.

The research was conducted by watching how the virus in artificial saliva reacted to different relative humidity climates. The researchers set the humidity inside a bioaerosol chamber to 60%, 40%, and 25%. At 60% and 40% humidity, the number of virus particles in saliva dropped by half in an hour. At 25%, which is Colorado’s average relative humidity, it took two hours for the number of particles to drop by half.

“This study is very relevant to Colorado because we have such low relative humidity,” study coauthor Marina Nieto-Caballero said. “We were honestly not expecting that lower relative humidity would double the infectious potential of the virus. That was something that surprised us.”

The study also found that at lower relative humidity saliva has a significant protective effect on airborne murine coronavirus because the saliva formed a gelatinous shield around the particles, providing extra protection.

Mark Hernandez, the study’s senior author, operates a lab at CU Boulder known for its chamber that aerosolizes “bad stuff,” such as whooping cough and tuberculosis.

Hernandez got the opportunity to do this study in 2020, during the early stages of the COVID-19 pandemic. Philanthropists donated money to Hernandez to study the virus — not to work on developing a vaccine, but to research how the pandemic was spreading. While Hernandez donated some of the research money to provide Colorado elementary and secondary schools with air purifiers; most of it went to adapting his lab to the new study.

Hernandez said the study got two strokes of luck: a specialized instrument that is able to catch airborne microbes becoming available just in time for the study, and an Uruguayan virologist getting stuck in Colorado due to COVID-19, making him available to join the research team.

The new instrument improved the quality of the team’s research because it better protected the quality of the collected microbes for counting than previously available instruments. That quality helped improve the accuracy of the team’s findings on infectious levels.

Eddie Fuques Villalba, now studying for his PhD in microbiology at Oregon State University, was the “perfect addition to the team”, Hernandez said, pointing to his work with viruses during his undergraduate studies in Uruguay and working with earlier coronavirus strains and their effects on chickens.

Hernandez’s team also included three former CU students who returned to participate in the study, including Nieto-Caballero, now a researcher at Colorado State University.

To combat virus survival rates in dry climates like Colorado, the study suggests increasing the use of air filters and ventilation in rooms as much as possible.

“We need to learn to adapt. And you see it everywhere. Climate change, energy, health, right?” Hernandez said. “Civilization needs to learn to adapt to these major changes, the pandemic just being one of them.”

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