Coronavirus
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Maintaining indoor humidity levels key to fighting the virus
The concept of airborne transmission is intimidating, but we can help control it by keeping the relative humidity in our breathing zone or in our buildings in the magic zone of 40-60 per cent. Existing regulations on indoor air quality should be updated to reflect the significant body of scientific evidence that 40-60 per centRH is the ideal indoor humidity for health. These improved humidity standards would have numerous positive effects on human health and well-being. Not only would it reduce the burden on society of COVID-19 disease and other upcoming seasonal viral illnesses, but research shows that it would also reduce With much in the news covering the social impact of the absenteeism and improve productivity in coronavirus outbreak, Dr. Stephanie Taylor discusses the need offices and schools. A recent study of a nursery to ensure public buildings, such as schools and hospitals, have a school found that fewer children missed school when the classroom humidity was maintained humidity level so that viruses cannot spread above 40 per centRH. (Rieman J, ‘Humidity as a non-pharmaceutical intervention for influenza A’, 2018 ASHRAE To manage the spread of COVID-19, we are humidity is not maintained, it becomes abstract). Studies support all working as a global collective to manage harder for our immune systems projected reduction of our behaviours responsibly, such as through to defend against respiratory Among absenteeism by at meticulous attention to hand hygiene and viral infections even if we t h e indoor least 20 per cent by social distancing. As individuals, these are maintain high personal v a r i a bles that inc simply maintaining undeniably key steps for us to protect ourselves hygiene standards. Public rease th likeliho healthy humidity and each other as we fight the current buildings like schools, e o levels in buildings. pandemic. However, individual behaviour is just workplaces and hospitals from ha d of infection , nd hyg one factor in our efforts to contain the virus have undoubtedly been iene to room c and limit subsequent disease. The environment hotspots for the spread of surrounding us plays a lesser-known, yet the COVID-19 outbreak, astoundleaning, one in essential role in the degree of viral spread and not just because of viral factor s g common in the severity of COVID-19 illness. Since we cross infection via physical ta spend most of our lives in buildings – such as contact, but in large part due dry ind nds out: oor air schools and workplaces and our homes – we to the airborne transmission of could and should be doing more to ensure infectious droplets, aggravated the conditions of these indoor environments by low indoor humidity levels. are optimal for human health. The simple Despite this, there are currently no factor of maintaining healthy levels of indoor regulations on minimum indoor humidity humidity is something that would benefit our levels in the UK and many other countries. In health through reducing the burden of COVIDfact, regulations focused on reducing energy 19 as well as other seasonal viral illnesses. consumptions in buildings have resulted in In my practice as a paediatric oncologist, the lowering of permitted minimum indoor I was alarmed by how many of my young humidity levels, unfortunately at the expense patients came down with infections during of occupant health. A lack of humidity their hospitalisation despite our best medical standards means that building occupants, treatments. It was at this time that I became like the hospital workers who have been on concerned that there might be another factor the frontlines of the COVID-19 pandemic at play; the indoor climate and the hospital and patients with compromised immune building itself. After years of work, including systems, have limited defence against further obtaining a master’s degree in architecture, respiratory viral infection, despite hand reviewing numerous studies of patient washing and social distancing measures. infections and the built environment and undertaking my own research, my suspicion Airbourne transmission was confirmed. Among the indoor variables It is long-established knowledge that that increase the likelihood of infection, from viruses can be spread through short hand hygiene to room cleaning, one astounding distance droplet splashing. But the common factor stands out: dry indoor air. transmission pathway we must now take into serious consideration is distant spread Indoor relative humidity of infectious aerosols travelling through An abundance of data from research in the air. When droplets are released into infection control, microbiology and building the air by an infected person sneezing, science show that maintaining indoor relative coughing, or simply breathing, dry air humidity between 40-60 per cent improves causes these droplets to shrink and human health through several mechanisms. desiccate to reach a moisture equilibrium. This relative humidity zone optimises the ability We now know that viruses carried in of our immune system to fight viral infections, those tiny desiccated particles can travel decreases the bio-burden of infectious particles through the air into an HVAC system and in our breathing zone (the air) and actually re-infect people from a distance, despite decreases the infectivity of many viruses and having had no immediate contact. bacteria floating in the air and settled on This transmission route is one of the factors surfaces. When this optimal range of relative that makes this virus particularly alarming.
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