
The Risks – Know Them – Avoid Them (COVID-19 infection event case studies) - mdturnerphys
https://www.erinbromage.com/post/the-risks-know-them-avoid-them
======
nkurz
_In order to get infected you need to get exposed to an infectious dose of the
virus; based on infectious dose studies with MERS and SARS, it is estimated
that as few as 1000 SARS-CoV2 viral particles are needed for an infection to
take hold._

As far as I know, this statement is somewhere between "completely wrong" and
"very misleading". There is no minimum number of viral particles necessary for
infection. Rather, there is a curve of probability of infection depending on
the number of viral particles. Going by the definition in the link[1] the
author provides, "The minimal infective dose is defined as the lowest number
of viral particles that cause an infection in 50% of individuals (or ‘the
average person’)."

Which is to say that there is no dose that is "safe", only doses that are less
likely to cause an infection. Very brief exposures to 100 contagious people is
just as likely to cause infection as a 100x exposure to one. Chance of
infection is not a linear function of number of viral particles (since one
can't be infected more than once) but can be approximated as linear at low
numbers of particles. I feel like this makes most of the rest of the article
moot.

Am I wrong? Is the risk of infection actually sublinear below some threshold
dose? Is there thus some "safe" exposure time that can be relied on? Or is the
article as wrong/misleading with regard to the risks to an individual as it
seems?

[1] [https://www.sciencemediacentre.org/expert-reaction-to-
questi...](https://www.sciencemediacentre.org/expert-reaction-to-questions-
about-covid-19-and-viral-load/)

~~~
londons_explore
I believe the theory is that if a virus multiplies with some exponential rate,
say doubling every 6 hours, and the immune system takes some fixed time to
respond, say 5 days, then the highest virus population in a person is directly
proportional to the starting dose.

Obviously the above is highly simplified, but are a model which would explain
any sublinear effects, if they exist.

~~~
nkurz
This is a good point, and would explain how there could be a threshold effect
on initial dosage. On the bright side, if this is true, it would make
inoculation against the disease fairly easy: give a measured light dose, and
reliably generate a mild case. On the not-so-bright side, while it is a
theory, I don't think it is anywhere near proven. If you've come across it,
I'd love to see more evidence that this theory is true.

I'm starting to double down on my "just plain wrong" interpretation. The
author of this article says repeatedly that one can be safe by simply avoiding
extended exposure: "Again, assuming every virus is inhaled, it would take ~5
minutes of speaking face-to-face to receive the required dose." "In these
situations there is not enough time to achieve the infectious viral load when
you are standing 6 feet apart or where wind and the infinite outdoor space for
viral dilution reduces viral load." "You would have to be in their airstream
for 5+ minutes for a chance of infection."

I think this article is full of bad, dangerous, and unproven advice. I think
the author has confused population level statistical risk (where reduced
exposure can reduce R0 below 1 thus preventing epidemic spread) with personal
risk (where exposure to a deadly disease can be deadly).

~~~
FabHK
> give a measured light dose, and reliably generate a mild case.

That’s how it used to be done, eg for smallpox. Inoculation or variolation:

[https://en.m.wikipedia.org/wiki/Variolation](https://en.m.wikipedia.org/wiki/Variolation)

------
taeric
This page keeps crashing on my phone. I can get down to the toilette flushing.

The idea seems solid, but a bit too alarmist, all told. Are there studies that
show this has the right vectors? (For that matter, the paper to go on a
toilette... There any evidence that is useful?)

~~~
yread
There was a infamous spreading event in an apartment block in Hong Kong where
due to faulty plumbing some sewage went "backwards" from the sewer to toilets
and a single person infected dozens. That was SARS

~~~
FabHK
There were suspicions of SARS-CoV-2 transmission as well, but don’t think
they’ve been confirmed.

[https://www.scmp.com/news/hong-kong/health-
environment/artic...](https://www.scmp.com/news/hong-kong/health-
environment/article/3075228/coronavirus-another-public-housing-estate-hong)

Here’s a paper on the 2003 HK SARS toilet event, and applications to COVID-19.
Gotta love science.

[https://www.thelancet.com/journals/langlo/article/PIIS2214-1...](https://www.thelancet.com/journals/langlo/article/PIIS2214-109X\(20\)30112-1/fulltext)

