Covid-19 spreads like glitter

I’ve written a couple of pieces expressing evidence-based doubts about the value of general public mask mandates as an epidemic control strategy. In them, I acknowledge that we know masks work when Covid-19 is present, and encourage people to make and wear face coverings if that would make you feel safer. Let me add a third note: if government in your part of the world mandates wearing masks, I strongly encourage adherence. Epidemic control is not an opt-out endeavour.

My last piece expressed concern that debate over masks has been a distraction from the real drivers of the outbreak in Victoria — the networks of transmission among precarious workers and workplaces in aged care, child care, meatworks, fast food and freight. It’s very easy to focus on individual behaviours and whether people are doing the right thing, and much harder to think and talk about social structure and complex networks. Indeed, I have come to suspect Premier Dan keeps talking about individuals doing the wrong thing because it functions so well as a distraction from government failures. But I have been encouraged by the public conversation about precarity and the need for paid pandemic leave and other forms of job security. 

As I noted, mask advocates often claim that Covid-19 is airborne. The people who advocate masks are the same people who advocated ‘go hard, go fast’ on society-wide shutdowns. I am in two minds about how sincere they are, since there’s an important contradiction in their claims. If SARS-CoV-2 can be passed on via droplet nuclei, which are particles 1-5 microns in size that can hang in the air, then wearing a surgical mask or improvised face covering is not going to have any protective effect whatsoever. But there’s another effect in play, which I’ll call reverse reasoning. Let me give an example.

As a public health practitioner, I look carefully at the science on transmission routes, and then I consider what devices and practices could interrupt them. But members of the public don’t have the training or the time to engage in that kind of systematic consideration. I’m not an expert on the environment, for example. I encounter facts and recommendations in everyday life, and as a moderately curious person I try to work out the links between them. When my local council provides a recycling bin, with a detailed list of what can and can’t go inside it, I reason backwards from that to develop a mental model of recycling as an environmental practice. I assumed the contents of my recycling get sorted and returned to Australian packaging manufacturers. It was a big surprise to discover it gets shipped en masse to China and ends up as landfill.

Because the federal government made such a mess of explaining the rationale for its control recommendations early in the outbreak, many people have used reverse reasoning to fill in gaps in their understanding of Covid-19. The clearest example is the anxiety and rage people feel and express about momentary breaches of the recommendation to keep 1.5m physical separation in public. Reasoning backwards from this recommendation, they have concluded that Covid-19 must be easily transmitted via brief, casual contact in public places. We’ve known since early in the epidemic that this is not the case, but people don’t understand why not, leaving them open to competing explanations. The notion that Covid-19 is airborne is a perfect fit for that mental model.

In a crisis, a group of cranks can easily out-communicate a government. They have one issue and that affords them excellent message discipline, while the government has to communicate across a whole range of issues. They can just keep banging the drum, keeping their issue on the media agenda until the government gives in, precisely because it needs the airtime for other issues. A simple message will beat a messy, complex set of messages every time — just ask John Hewson or Bill Shorten. But we should ask why some people seem so determined to ‘beat’ government in the first place. The answers are not pretty. They include relevance deprivation syndrome, hunger for public profile, and feeling overlooked for a role in advising the government response. 

(But enough about me.)

The truth is always messier than a message. In the remainder of this piece, I want to explain the difference between airborne and droplet transmission. When you understand the basics, then you develop literacy that allows you to make sense of the more complex and uncertain aspects of the bigger picture. My hope is that enough people will read it and become the seeds of a diaspora, becoming informal educators in a culture of care around Covid-19. 

By contrast with formal education, which follows a plan of topics and activities, informal education has no curriculum. It happens spontaneously, when you spot a fleeting moment of opportunity in a conversation on equal terms, and you know just the right thing to say to tweak how someone understands the issue. It can’t be planned-for, but you can be prepared. And metaphor can be a powerful (albeit unpredictable) strategy for informal education.

So here’s the metaphor: Covid-19 spreads like glitter.

Airborne transmission is sometimes explained as involving droplets of respiratory secretions less than 5 microns in size, which can hang in the air and travel on air currents more than 1.5 metres from their source — even after the infected person has left the room. Droplet transmission is said to involve larger droplets that fall onto nearby surfaces, or get caught in our hands when we smother a sneeze and then transferred to another person when we shake hands or hug each other. This size distinction has been criticised. And, to be honest, this doesn’t seem enough to explain the incredible contagiousness of the condition, right? Surely it’s airborne.

Here’s how comedian Demetri Martin describes glitter:

Glitter is the herpes of craft supplies. 😘👌

People often think airborne transmission includes direct spatter from coughs and sneezes, but it doesn’t — that falls under droplet transmission. Glitter can fly through the air when propelled by a glitter cannon, and it can go everywhere after that, but it doesn’t hang in the air. Covid-19 is the same. 

And it’s still plenty transmissible. No matter how careful you are, if you use glitter in your craft project, you are going to spread it all over the place — by touch alone. If you air-kiss someone wearing glitter make-up, you are going to get it on you. If you get it on your hands, cuffs, phone cover, wallet, face mask, then you are going to transmit glitter to other people you meet and touch. And you’ll do all of those things unconsciously, even if you make a real effort to keep it contained and vacuum your craft space. Covid-19 is the same.

The finest glitter particles are 200 microns in size. That’s way bigger than the droplets that we create when we cough or sneeze (or snot all over ourselves). And yet they are highly, highly transferable.

We do not need airborne transmission to explain why Covid-19 is contagious.

Metaphors only go so far. One big difference is that glitter is forever — plastic glitter will take a thousand years to break down — whereas particles of SARS-CoV-2 will break apart with soap and water or hand sanitiser, and will be inactivated fairly quickly when deposited on surfaces. Another big difference is that glitter spread ceases when its point source is exhausted, whereas Covid-19 can keep infecting new hosts and creating new sources. But you can use this metaphor to understand and explain the considerable potential for spread via particle deposition and transfer.

This is why social distancing is so important. We know from studies of infection control in hospitals that medical staff require significant training and monitoring to use personal protective equipment correctly. To avoid catching glitter, your best strategy is to avoid dance parties indoor social gatherings, stay home as much as you can, and limit visits by people who could track it into your house.

Bonus for reading this far: enjoy this gorgeous track by NZ artist, Benee.

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2 thoughts on “Covid-19 spreads like glitter”

  1. One thing about masks is that many mistake them for sieve, one layer with holes. In many cases, masks are multilayered and therefore droplets of whatever sizes would have to navigate between layers and holes (stacked sieves). Then there is also electrostatic which tends to attract and ensnare anything passing by, making a direct comparison between virus size (which do not hang alone in the air BTW), droplets size and mask holes irrelevant.

  2. I used to do woodturning, which can generate a heap of invisible airborne particles smaller than 5 microns that float in the workshop for hours.
    Breathing in these particles is associated with nasopharyngeal cancer and so is best avoided. But the association isn’t strong and varies by industry and wood species so there are other things going on. We don’t know what but as with Covid-19 concentration is probably a factor.

    What I learned in investigating and implementing protections was this: no one method is 100% effective.

    Filtration standards specify the percentage of particles down to a given size that will be removed. Clean barrier filters don’t perform as well as slightly clogged ones and that’s intended. Multiple defences are advisable (and I implemented three). Complacency about rigorous use and maintenance can undo all your heavy spending on hardware. With masks the seal around the face has to be good, and that isn’t achievable by the bearded like me who should be wearing a filtered visor.

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