Wait - why is Jason talking about COVID-19? And why are these written like FaceBook posts? There’s a longer explanation here but the short version is that my day job for the past 15 years has been developing models of human health effects and medical response for chemical injuries and biological illnesses, including pandemics. I’ve been making these posts on FaceBook and I was asked to put them in a more shareable manner. I’m linking to the posts on the explanation page. These are the original, unedited posts. I’ll continue until I run out of things to say.
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Originally posted here on 3/19/2020.
Another COVID-19 post, this one on infectivity! Or, put a different way – when can others get you sick/when can you get others sick?
This is my fifth post on COVID-19. Once again, I’ve spent the past fifteen years developing models of human effects and medical response, particularly in mass casualty scenarios. I am not working COVID-19, but I’m leaning on my experiences from developing models of pandemic influenza, smallpox, and pneumonic plague. These are meant to be informative, honest, and non-political posts about the mathematics and science of pandemics. I am collecting all of my posts here: https://www.jasonrodriguez.com/…/covid-19-a-hopefully-brief…
First, let’s define some terms – an infectious person is a person who is actively shedding virus. What does it mean to “shed” virus? It means that as an infectious person is going about their day, they’re peppering the air and surfaces with viral particles that can in turn be picked up by susceptible people. A susceptible person is anyone who has not yet been exposed to the virus and can still become infected by the virus. An infectious person can shed the virus by a) coughing or sneezing and releasing particles into the air that contain the virus, b) doing that thing we do when our nose is running but we don’t have a tissue so we pinch our nose and wiggle it and then touch a surface immediately after, c) probably making out, TBH, d) picking a booger and wiping it underneath a table, maybe…essentially anyway you can imagine the stuff from your mouth and nose can get into the air or on the surface. PROBABLY NOT BREATHING, THO. That would be one hell of a disease…or a messy breather. You don’t want to be friends with that person.
Can a spit talker shed viral particles? Probably. I have to imagine a person who spit-talks would be expelling some pretty big spit particles, though. “Respirable particles” (particles that can enter your nose or mouth) tend to be less than 100-microns in diameter – that’s the size of 20 red blood cells placed sideways – not very big. The liquid part of the spit could certainly evaporate down to respirable viral particles, I’m sure. Spittle could certainly land on surfaces, too. But honestly the only place I’ve ever encountered a high-concentration of spit talkers is on Broadway and they closed Broadway down. Also, I should probably state that I know nothing about spit talkers. This is all conjecture.
Why am I talking about all of this? Well, because I think people should know a bit more about infectivity periods during this pandemic. If you listen to some folks, including some folks in the media, you start get the impression that AS SOON AS SOMEONE IS INFECTED WITH COVID-19 THEY ARE INFECTIOUS! I put that in all caps because that’s a scary as hell thought! It’s wrong, but it’s scary. It’s very wrong, but it’s still scary.
The point is, it’s wrong.
There has been one study so far that I’ve seen (“Serial interval of novel coronavirus (COVID-19) infections” by Nishiura, et al. if you want some hardcore math) that has looked at mean time to infectivity and they pegged it at about 4.6 days. The mean time to symptom onset is about 5 days. So everything being average, people start to become infectious about 0.4 days before they exhibit symptoms, according to a well-written paper that looked at a very limited data set (that may sound like shade, but it’s just some padding for my science peeps).
You may think 0.4 days doesn’t sound bad but let me put it this way: 9.6 hours. Still doesn’t sound bad? Well let me put it this way: that’s a work day plus commutes. That is bad! That means you can wake up, ride the train, spend the entire day at work, ride the train home, get home and say, “Oh…what’s this sour throat?” Every surface you interacted with could have YOUR viral particles on them, and every susceptible person who touched them could have picked them up.
In those early phases, it’s really predominantly a contact hazard, as in you are physically touching things after touching your nose or face and then touching a surface. You may even cough a little but not think anything of it (“Oh, it’s just allergies,” or, “Choked on some water,” are things we say more than we think). Once you transition to coughing and sneezing, though, look out boy – you are creating tiny aerosols of viral particles that can live for hours…not necessarily in the air, though. Particles settle, it’s what they do. You do not need to worry about virus clouds as you walk around. Seriously, go for a walk. You smell and your legs are atrophying. Please, for the love of your Quarantine Crew, go for a walk.
ANYWAY...those sneeze particles settle on surfaces, and a sneeze will cover a lot of area, for sure.
So this is really why it’s important to stay home. You could spend 8 hours in the world, thinking you’re fine, and that could lead to other people getting sick. Those folks can take it home and get other people sick several days later. And it goes on and on and on. The thing about this illness is the high fatality rate compared to other highly-infectious illnesses. You don’t want that on your conscious. Do what you can.
And if you do go out? Look, I’ll be honest, I’ve been wearing one disposable glove on my left hand. It doesn’t protect me, but it makes me conscious of the fact that I am outside in a pandemic. That’s my public hand – anything I don’t want to bring back to the house, I touch with that hand. Elevator buttons, ATM keypads, etc. Never my face! Who wants to touch their face with a rubber glove, anyway? And then it’s a reminder to wash the hell out of my hands when I get back. Do you need to do that? Probably not, but it’s my coping mechanism. It’s the string around my finger. But the most important part is that when I get home, I wash the hell out of my hands.
Inside the house, I’m protected. We’re not sick, and we’re not interacting with other people. At the end of our two-week self-quarantine, we can interact with folks in smaller groups who had the same quarantine measures as we did – true isolation, etc. Eventually, with enough people quarantining, we’ll flatten the curve enough so that we can go out and do other things.
Anyway, that’s our plan. I hope you all adopt similar plans.
Until next time, safe healthy and safe, my friends.
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These are my opinions and thoughts and analyses - I am not representing any government agency or my company. More disclaimers on the main page.