The Risks – Know Them – Avoid Them (COVID-19 infection event case studies) | Hacker News Reader

The Risks – Know Them – Avoid Them (COVID-19 infection event case studies)

erinbromage.com

72 pointsmdturnerphys12 comments

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...

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.

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).

> 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

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?)

regrettably the toilet infection vector is a known thing in epidemiology. it's called a "fecal plume" or "toilet plume".

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4692156/

https://www.cdc.gov/niosh/nioshtic-2/20043244.html

Toilets vary more than you would expect around the world. Some countries have mostly high pressure, fast moving water designs, which I presume leave a lot of droplets in the air, while others have far slower more "swirly" designs that I suspect transfer less into the air.

It would be good to see research on this...

If you can get further down there are links to papers about specific infection instances, but none about toilets.

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

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...

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...

What part or parts did you find to be too alarmist?

The only part I could get to before a big banner blocking me was about toilets. Which, still seems overly frightening.

That all said, thanks to all for summarizing and giving links! Still not sure why the page wouldn't load, and happy/weirded out to get challenged on some of these.

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