This study describes “detecting viable virus” as having a threshold of 10^0.5 TCID50/mL, and they assume exponential decay of viable virus particles.
I’m really confused by their numbers, tho; it looks like cardboard has a hundred-fold reduction in 23 hours, from 10^2.5 to their detection threshold of 10^0.5, which I can’t square with the 8.5 hour half-life. [Edit: it looks like I’m potentially confused about what TCID50/mL means?]
I also don’t know how to compare their detection threshold with the point at which I should be willing to handle a cardboard box (with varying levels of cleaning and PPE). Is their test basically as sensitive as my immune system (in that I shouldn’t handle something where they could see a viable virus, and can handle something where they can’t)? Or should I be letting boxes sit for 3 days?
I had the same confusion over the half life ratings.
TCID50/mL is how much you can dilute a sample and still have it kill half of the cells in a sample. This suggests that the natural reading of those graphs is correct.
I estimated some numbers off the graph and it looks like what they are calling half-life is actually 1/5th life, so either we’re both missing something important or there is an error somewhere.
[UPDATED, thanks to various people who caught errors in V1 and pointed out V2] New NIH study of COVID half-life in aerosol or on surfaces V1 with errors: https://medrxiv.org/content/10.1101/2020.03.09.20033217v1 , V2 hopefully error free: https://www.medrxiv.org/content/10.1101/2020.03.09.20033217v2.full.pdf (H/T @AndyBioTech)
2.4-5.11 hours on copper, in contrast to 10.5-16.1 on steel or 13-19.2 on plastic
This study describes “detecting viable virus” as having a threshold of 10^0.5 TCID50/mL, and they assume exponential decay of viable virus particles.
I’m really confused by their numbers, tho; it looks like cardboard has a hundred-fold reduction in 23 hours, from 10^2.5 to their detection threshold of 10^0.5, which I can’t square with the 8.5 hour half-life. [Edit: it looks like I’m potentially confused about what TCID50/mL means?]
I also don’t know how to compare their detection threshold with the point at which I should be willing to handle a cardboard box (with varying levels of cleaning and PPE). Is their test basically as sensitive as my immune system (in that I shouldn’t handle something where they could see a viable virus, and can handle something where they can’t)? Or should I be letting boxes sit for 3 days?
I had the same confusion over the half life ratings.
TCID50/mL is how much you can dilute a sample and still have it kill half of the cells in a sample. This suggests that the natural reading of those graphs is correct.
I estimated some numbers off the graph and it looks like what they are calling half-life is actually 1/5th life, so either we’re both missing something important or there is an error somewhere.
I’ve emailed the author; we’ll see if she has time to respond (or if the code goes up on Github; I can’t find it yet).
Looks like v2 of the paper has corrected the error.
See here: https://www.lesswrong.com/posts/B9qzPZDcPwnX6uEpe/coronavirus-justified-practical-advice-summary?commentId=LuJRfhrNhu4aBanQn