It took a long time for air cleaning to be recognized as a powerful tool for reducing the risk of Covid-19 transmission, and it should be embraced more thoroughly during this pandemic and to reduce flu cases. Ventilation and filtration are two proven techniques for physically removing viruses from the air, so that people are exposed to fewer of them. Poor ventilation was a factor in many coronavirus superspreading events, such as the outbreak at a choir practice in Skagit Valley, Wash.
There are some simple ways to improve ventilation, like opening windows and doors. A recent small study, which has not yet been peer-reviewed, showed that the amount of coronavirus in the air was substantially lowered when ventilation was significantly increased by running an exhaust fan that removed stale air from a room, pulling in outside air through an open window. Other effective options can require more effort. Ultraviolet treatment is another approach used in hospitals to kill viruses in the air. This technique could be more broadly applied in crowded public areas, although it must be properly installed to be effective and avoid the potential for harm. The initial cost is higher than other approaches, but it is worth considering as part of a cost-benefit analysis of different technologies.
Increasing humidity may also be helpful for reducing transmission. The evidence isn’t as strong as for the other tools, but some data show that humidifying the air in the range of 40 to 60 percent — but not higher because that promotes mold growth — could help. In this range, certain flu viruses, the new coronavirus and other viruses don’t survive as well, and our immune response is stronger than when the air is drier. This effect is still not fully understood and should be researched further.
I’ve long believed, based on years of research, that the role of aerosols in the spread of many respiratory viruses is underappreciated by the medical community. I hope that Covid-19 has catalyzed a shift in thinking about the air we breathe. You wouldn’t drink a glass of water full of pathogens, chemicals and dirt. Why should we put up with breathing contaminated air?
There are still some unknowns: How much respiratory virus transmission is attributed to inhaling aerosols versus being sprayed with large droplets versus touching contaminated surfaces is unclear. How do we grow that knowledge and design buildings to minimize disease transmission? That’s a question that governments and scientists should address.
It will be a challenge to rethink the design and operation of buildings to account for air quality, but it is not insurmountable. Around the turn of the 20th century, the proliferation and modernization of water and sewage treatment systems helped make common waterborne diseases such as typhoid and cholera a rarity in the United States and Europe. The results of investments in water infrastructure are considered one of the greatest public health achievements of the 20th century. Making air quality healthier as a way to cut down on disease should be a public health focus for this century.
Linsey Marr is an engineering professor at Virginia Tech, where she studies the airborne transmission of viruses.