What can we learn from COVID superspreaders?
In the late 1800s, an Italian economist named Vilfredo Pareto observed that 80% of the wealth in Italy was owned by 20% of the population. This concept - that some inputs disproportionately drive outcomes - was subsequently christened the Pareto Principle, or the 80/20 principle.
We see these types of asymmetric distributions everywhere we look. Health care costs. Wealth distribution. Business sales.
So it’s not surprising that the spread of COVID follows an asymmetric distribution as well.
I’m sure you’ve heard of the terms superspreaders or superspreading events. What that means is that a small number of people and events have an outsize impact on the spread of SARS-CoV-2.
Distinguishing between the trivial many and the vital few is important in all aspects of life. It’s important in COVID because it let’s us calibrate our own personal risk and make decisions accordingly.
When I think about superspreaders of COVID, I think about two different buckets - superspreading people and superspreading events.
Who are the superspreading people?
I’ll keep this short: it could be anybody.
You can’t tell from looking at someone how likely he or she is to spread the virus.
Ability to spread the virus doesn’t have to do with the symptoms that you have, how sick you get, or whether or not you die.
As of right now, it’s not completely clear why the majority of people don’t spread COVID-19 but some spread it to many.
It’s estimated that between 10-20% of people account for 80% of COVID spread.
I suspect that the difference between superspreaders is less about biology and more about circumstance. In other words, it’s not that some people are genetically predisposed to shed more virus and infect more people, it’s more about the circumstances surrounding the period of time when someone is infected and contagious.
Of course, that’s not to say that there aren’t genetic differences among different individals that may dictate some of the kinetics around spread, it’s more to say that there’s no obvious relationship we can really learn from to reduce overall public health risk.
The much more important issue: superspreading events
Massive clusters of disease seem to emerge from circumstances where many people congregate together indoors in close contact with poor ventilation.
Like the nursing home clusters from New York or Japan, the Biogen conference in Boston, or a choir practice in Washington.
Clusters of infections have also come out of prisons, food processing plants, cruise ships, dorms, and shopping areas. I’m sure there are many other examples.
The commonalities that we seem to have identified among these events or places can be summed up with the 3 C’s:
Closed spaces with poor ventilation
Crowded spaces
Close contact settings
You minimize these things and you minimize spread of the virus. It’s the clearest path forward from a public health perspective, and it’s depressing that we’ve known this in some form for months.
Since a huge amount of spread occurs when people are asymptomatic, and only a small porportion of people who are symptomatic have fevers, the temperature screenings that many of us are subject to are theater rather than safety (I do one everyday at work, for reasons that are totally unclear to me).
Superspreading is a dynamic property
The spread of the virus isn’t a fixed property of SARS-CoV-2. It’s only partly related to infectivity. The R0 in this pandemic - the quantitative measure of spread - it malleable based on our behavior.
I’m not advocating to stay on lockdown and avoid all public indoor spaces. The social isolation and economic stress have been terrible, and, for some, as bad as the direct effects of the virus itself.
I’ve said before in this newsletter that I’m not a public health expert and I’m not in charge of policy - I’m a doctor and I believe that my role is digesting this information and describing risk to my patients.
So I think that the message to send is one of prudence and managing risk.
If you can avoid crowded indoor spaces, then you absolutely should. It’s the best way to reduce your personal risk and the possibility that you are a public health hazard.
If you can’t avoid a crowded indoor space - we all need to go grocery shopping, after all - then wear a mask and don’t stay super close to anyone. Minimize the time you’re in the store.
Spread of the virus isn’t driven by viral particles on surfaces, it’s driven by airborne transmission. So focus less on Lysol wipes and more on keeping your mask over your nose.
I suspect that indoor restaurant dining carries quite a bit of risk. So if you can eat outside, you should. If you can’t, I don’t think you should go. To support local businesses, order takeout or delivery.
And if you think you might be sick, don’t go into public places, unless you want to make things worse for everyone.
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