Indoor Air Quaility & Era of Pandemics
Ecological destruction and unsustainable consumption have entered humanity into an “era of pandemics,” according to a report from the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, a global expert body advising governments.
There is no doubt that Covid-19 has catapulted our awareness of indoor air quality to the top of our priorities but according to experts, Covid-19 isn’t even ‘the big one’. We have to prepare ourselves for an even more devastating pandemic in the future.
“Without preventative strategies, pandemics will emerge more often, spread more rapidly, kill more people, and affect the global economy with more devastating impact than ever before,” says the same report.
The panel said that Covid-19 was the sixth pandemic since the influenza outbreak of 1918 – all of which had been “entirely driven by human activities”. Deforestation, agricultural expansion, urbanization, and other land-use changes are responsible for about a third of all new diseases since 1960. These activities put humans in increasingly close contact with wild and farmed animals and the diseases they carry. Seventy percent of emerging diseases, such as Ebola, Zika and HIV/AIDS, are zoonotic in origin, meaning they circulate in animals before jumping to humans. Around five new diseases break out among humans every single year, any one of which has the potential to become a pandemic.
Covid-19, caused by the SARS-CoV-2 virus, is a respiratory virus and is transmitted in several ways: Contact transmission is infection spread through direct contact with an infectious person or with a surface/article that is contaminated. Droplet transmission is infection spread through exposure to virus-containing respiratory droplets (i.e., larger, and smaller droplets and particles) exhaled/coughed/sneezed by an infectious person. Because droplets are too big to remain suspended in the air, transmission is most likely to occur when someone is close to the infectious person, generally within about 6 feet – hence our need to socially distance.
Airborne transmission is infection spread through exposure to those virus-containing respiratory droplets comprised of smaller droplets (aerosols). Aerosols are tiny in comparison to droplets and so can remain suspended in the air over long distances (usually greater than 6 feet) and for longer time (typically hours).
It is primarily this airborne transmission that has forced us to transform the way we think about our indoor air. Diseases that are spread efficiently through airborne transmission (TB, measles, chicken pox for example) tend to be very contagious as they can quickly reach and infect many people in a short period of time. It appears that SARS-CoV-2 is mainly spread by contact and droplet transmission, but more and more evidence is coming to light to suggest that airborne transmission is a more important form of spread than what was previously thought.
Airborne transmission of SARS-CoV-2 appears to be more likely in certain circumstances – for example, in enclosed spaces within which an infectious person either exposed people at the same time or to which people were exposed shortly after the infectious person had left the area. Or where there has been prolonged exposure to respiratory particles, often generated with expiratory exertion (e.g., shouting, singing, exercising) that increased the concentration of aerosols in the air space. Inadequate ventilation or air handling that allows a build-up of virus-laden aerosols also creates an environment ripe for the rapid spread of the virus.
What is not known is what proportion of SARS-CoV-2 infections are acquired through airborne transmission. Research is ongoing to help us understand how viral-laden aerosols and droplets behave in the air, how transmission occurs, how air cleaning/masks/other mitigation measures can reduce viral load in the air.
Although we are primarily concerned with SARS-CoV-2 in indoor air, aerosolized SARS-CoV-2 does not exist in isolation. Recognition of all airborne microorganisms and how they may interact with many of the chemicals in our indoor air needs also to be studied. It is clear that a greater understanding of airborne viruses and microorganisms in indoor air is needed to develop strategies to protect human health in this era of pandemics.