Airborne disease transmission: Something’s in the air
Blog post summary of Episode 3 by Anika S.
You know the Greek myth of Icarus? The boy who flew too close to the sun with wings made of wax and feathers? The wings melted and he tumbled into the sea. That’s kind of what happened to public health.
Globally, public health had done its job to stamp out diseases like smallpox, and we had largely eliminated tuberculosis, measles, and polio in many regions. For those of us with access to clean water, sanitation, vaccinations, and health education, things were pretty good overall. But, like Icarus, public health grew arrogant—and hubris kills.
Despite these advancements, we’re currently in the midst of a pathogen palooza of tuberculosis, measles, norovirus, H5N1, influenza, walking pneumonia, and the persistent presence of COVID-19.
While all of this is a loud funeral knell for the field of public health, there were a lot of nails in the coffin that got us here–one of the largest: fumbling airborne disease transmission, which may be one of the greatest public health failures in recent history.
For most of modern public health’s existence, airborne transmission has been feared, mocked, or outright dismissed. This skepticism is partly rooted in the legacy of miasma theory, a longstanding belief that putrid smells or “poisonous emanations” could waft on the breeze, enter the body, and cause disease. While it’s true that bad-smelling air can’t actually make us sick, the physics that allows tiny particles to hang in the air holding microscopic pathogens that do cause disease is sound.
Our public health leaders have clung to a droplet-centric view of disease transmission, based on the flawed assumption that diseases spread only through droplets expelled while talking, coughing, or sneezing. The idea is that these droplets then land directly on mucous membranes in the mouth, nose, or eyes, or get transferred there via our hands.
This belief shaped public health guidelines early in the COVID-19 pandemic, causing leaders to tout measures like hand-washing over airborne transmission protection strategies, like masking and ventilation, and prevented them from properly investing in preventative testing initiatives.
Even if public health officials weren’t fully convinced about airborne transmission, they were aware that similar diseases, like SARS-1 and influenza, can be airborne. To minimize harm, they could have acted as though airborne transmission was a possibility, while scientists took a closer look—this is called the precautionary principle.
In Episode 3 of Public Health is Dead, Dr. Katie Randall, a medical rhetorician and historian, explains the confusion surrounding droplet versus airborne transmission, which primarily hinges on the 5 micron particle size error.
Dr. Randall’s rigorous citation excavation work found that in the 1960s, people working in public health conflated the size of the largest particle that tuberculosis is infectious in (5 microns) and the largest particles that can enter and cause damage deep in our lungs (also 5 microns), with what is transmissible in the air.
This critical mixup meant that particles over 5 microns were categorized as droplets, while those smaller than 5 microns were labeled airborne.
The thing is, in the 1930s, researchers William Wells and Mildred Weeks-Wells showed that particles up to 100 microns have the capacity to carry infectious agents and remain airborne. We’ve been operating on a 20-fold misunderstanding of how big particles can be and still be suspended in the air!
This also means the early pandemic guidance to stay six feet apart is not as helpful as we thought. Being more than six feet apart does give some distance and time for larger droplets or particles to sink, but it doesn’t mean we get a magical force field of protection in front of us from airborne aerosols.
Despite Dr. Randall pulling the rug out from under public health guidance and infection control as we know it today, public health leaders kind of just…shrugged. It’s possible their apathy stems from a difficulty admitting they have been wrong and acknowledging that their decisions have contributed to significant damage, death, and suffering, including issues related to Long COVID and other post-COVID health problems.
It’s also much easier for public health officials to tell people to wash their hands and stay at home because these are individual behaviours. If you get sick, it’s your responsibility. It’s not possible to tell people they are responsible for choosing which cubic meters of air they breathe. This would require the government to take on the responsibility of ensuring that workplaces and buildings have clean air.
Still, things did start to shift a little after Dr. Randall’s discovery. Since 2021, the WHO website has said in no uncertain terms that SARS-CoV-2 spreads between people through airborne transmission, but the WHO and other public health organizations didn’t clearly correct this information for the public. They kind of whispered and mumbled it pretty late in the game when it was impossible to deny; if you weren’t paying attention, you probably wouldn’t know.
Public health leaders have been making decisions on the assumption of droplet spread for many diseases, which doesn’t actually hold up against what aerosol scientists see and doesn’t line up with the scale and speed of transmission for many diseases, including COVID-19. Having droplets repeatedly land on mucous membranes accurately enough to produce this much sickness seems quite unlikely.
Dr. Al Haddrell, an aerosol scientist, studies aerosol generation during normal activities like talking and breathing, which releases respiratory fluid from our lungs into a plume of aerosol when we exhale.
He stresses that transmission risk is high even when people are not visibly sick, such as in asymptomatic and presymptomatic cases, which is why measures like masking or staying home only when you’re sick don’t fully address the problem.
Everyday situations like attending a doctor’s appointment or riding a crowded bus provide ample opportunities for disease to spread. It’s also why masking is such an effective preventative measure–respirators, tight-fitting masks designed to block aerosols, work incredibly well when they’re worn properly and consistently.
Driven by the Cold War and the fear of airborne bioweapons, scientists in the 1950s were interested in airborne transmission, but the methods they used to answer questions about how long biological agents could live in the environment don’t translate very well to questions about quick transmission of pathogens, like SARS-CoV-2.
So, Dr. Haddrell and his team designed a new way to investigate airborne disease transmission and viral infectivity called CELEBS (Controlled Electromagnetic Levitation and Extraction of Bioaerosols onto a Substrate). Using this highly-controlled method, they discovered that CO2, in the form of bicarbonate, plays a striking role in viral transmission.
Since SARS-CoV-2 requires a low pH to infect cells, they observed that by increasing the concentration of CO2 in a room, less CO2 escapes from an infected droplet, keeping the pH low and effectively increasing the risk of transmission.
Paired with ventilation measures, we can use this knowledge to reduce transmission cheaply and effectively.
Unfortunately, climate change is slowly chipping away at how useful some of these findings are–if the CO2 in air is high outside and inside, then ventilation is a less potent strategy.
So…what now?
If we want to tackle ongoing pandemics and avoid new ones, we must address climate change. Ending climate change is ending pandemics is ending systemic racism is ending ableism. These things are connected! We can only survive if the planet survives, and the various forms of systemic oppression that exist in our world are in direct opposition to a thriving planet.
Like Dr. Randall advocates, we also need to depoliticize giving a sh*t about the health of the people around us so we can build resilient communities.
If we want to start to fix the COVID problem, we need:
Education: People need to know about and understand the basics of airborne transmission.
Advocacy: Public health leaders need to clearly explain to decision makers and the public why and how to use ventilation and air filtration. They also need to provide accurate information about respirators and normalize their use as a preventative tool.
Infrastructure: We need clean air in public buildings–especially hospitals and schools–to reduce population-level disease transmission. We need better rapid tests so people can use them to know if they’re infectious before they show symptoms. We need better COVID vaccines that work to create long-lasting immunity and block infections.
But the first thing public health leaders could do is take accountability and be honest that, in this instance, they made a mistake about airborne transmission. COVID, and many other diseases, are not spread only by droplets.
Acknowledging and correcting their errors wouldn’t mean that public health isn’t valuable; it’d buy back public trust.
Perhaps there’s a version of the Icarus story where he doesn’t drown and instead gets pulled ashore by a group of people who care that someone is stranded and fighting for their life…maybe they build a few rescue boats together, set up a lifeguard team, and put on free swimming lessons so nobody drowns again.
The solutions to airborne transmission are in our hands–and it’s not handwashing.
The best time to act on airborne transmission would have been five years ago.
The next best time is now.
