Researchers see humidity as a weapon in the fight against airborne viruses


The continuing fight against the COVID-19 pandemic could be boosted if Canadians paid more attention to relative humidity levels in public and private spaces, according to a growing body of international research.

Doctors, scientists and engineers agree that sufficient humidity levels in indoor air can have a powerful but little understood effect on the transmission of airborne diseases. Although the new coronavirus that causes COVID-19 is currently being treated as the one that is transmitted by droplet rather than airborne infection, research is still ongoing on how it passes between humans.

However, most buildings are below the recommended 40-60% relative humidity threshold, especially in countries with colder and drier climates like Canada.

Tackling the problem now, they argue, could provide immediate short-term benefits and provide a powerful tool for warding off similar epidemics in the future.

“Transmission is higher in dry air, infectivity is higher in dry air, and a person’s ability to fight infection is impaired,” said Dr. Stephanie Taylor, graduate and lecturer at Harvard Medical School. “Any one of them would be important, but all three are at stake.”

Taylor concedes that the notion may seem counterintuitive, saying that the idea of ​​humidity conjures up images of foul swamps and disease-carrying mosquitoes. But she said that a growing body of research has suggested that much more comfortable relative humidity levels for humans offer a multitude of benefits.

She said airborne particles carrying viruses can travel further into air that is not sufficiently hydrated. For reasons the researchers are still probing, she also said that viruses also seem to be more infectious in these drier conditions.

Dr. Samira Mubareka, medical microbiologist at Sunnybrook Hospital in Toronto and member of a team that isolated the new coronavirus, previously helped conduct research on the effect of temperature and humidity on influenza strains .


The research, which evaluated the Toronto data over a period of about five years, found that higher humidity levels seemed to help create less favorable conditions for virus development, especially in colder global temperatures. .

“It’s in this 50 to 60 (percent) range that we have seen the least transmission,” she said.

The researchers also said that relative humidity levels have an effect on the body’s natural infection-fighting functions.

Karen Bartlett, professor at the University of British Columbia’s School of Population and Population Health, said that good hydration is necessary to keep everything healthy, from the mucous membranes to the eyes and skin.

“If we have between 40 and 60 (percent) of relative humidity, we also protect our buildings and make them more comfortable for us,” she said.


But according to the international body that sets standards for the built environment in many countries, including Canada, these benefits cannot be achieved in the majority of public and private buildings.

Robert Bean, a Calgary-based indoor climate consultant and distinguished speaker at the American Society of Heating, Refrigerating and Air-Conditioning Engineers, said Canadian buildings are asked to maintain humidity levels between 35 and 55%.

But he said that Canada’s relatively cold and dry climate can make it difficult to maintain these levels, especially in older buildings.

The larger the difference between indoor and outdoor humidity levels, he said, the greater the tendency for indoor air to flow outward and cause condensation, which in turn can cause mold and other potential hazards.

This trend is at its peak in older buildings such as schools, he said, but a misunderstanding of building standards is also a risk factor.

Bean said international research has shown that less than five percent of buildings currently meet the ASHRAE standard for environmental conditions for human occupancy, which includes relative humidity as a factor.

“If you had another industry with so little knowledge of their standards, that industry would collapse,” he said.

But Bean said the trend is slowly starting to change, in part due to a growing understanding of the overlap between the engineering and medical communities.

“This whole problem with the virus highlights the importance of the built environment,” he said. “It reveals the weaknesses we have in the relationship between the building sciences and the health sciences.”

Taylor said that individuals facing self-isolation or practicing physical distance could benefit from increased relative humidity levels in their own environment and called on public spaces to make these efforts a priority to move from the front.

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But Mubareka did not echo his recommendations, saying that too much is unknown about COVID-19 at this point.

“I wouldn’t be surprised if the conditions were very similar, but until they were properly tested, I would personally hesitate to recommend to the general public to start implementing things of this nature,” he said. she declared.

Mubareka said that all the evidence available to date suggests that protective measures against droplet infections remain the best line of defense against COVID-19, in particular regular hand washing, the use of masks for workers health and those with symptoms, and physical distance to the rest of the public.


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