That CDC brief on surface transmission is annoying vague about certain things.
Note about your analysis: that's 1 in 10,000 *per surface touched*. If you touch 100 contaminated surfaces per day, the risk would appear to rise to 1% per day! Very few people eat 100 eggs per day. (I know of one toxicologist who did it at least once, but that guy used to do some weird stuff.)
Also, what's a "surface" for this purpose? Each door handle, each light switch, each chair back? You could reach 100 easily, if you're in an area with high incidence of infection.
OTOH, it actually says "less than" 1 in 10,000, so ... did I mention it's annoying vague?
Then again, maybe it doesn't take handwashing into account? It says things like, " Hand hygiene is a barrier to fomite transmission and has been associated with lower risk of infection." and "The risk of fomite transmission can be reduced by wearing masks consistently and correctly, practicing hand hygiene, cleaning, and taking other measures to maintain healthy facilities." It doesn't (as you wrote) make clear if its risk assessment does, or does not, include hand hygiene, but I have to think not. If it did, then would this not imply that it also takes into account mask wearing (How is that relevant to surface transmission), cleaning, and "other measures"? And isn't "other measures" ... annoying vague?
I do think it's relatively vague, yeah, but all of this is an approximation. We're never going to have great models for anything in this situation. Let's keep in mind, of course, that even my egg example is approximation based on expectation values, since really, given how randomness works, you'd need to go through about three times that many eggs to be almost guaranteed to get one contaminated egg. There's always some chance that you don't encounter the event within the expected number of iterations; anyone who has flipped a coin twice and gotten the same result has experienced a failure of expectation values to represent reality.
When I said I think it takes into account hand hygiene, I was basing it on the fact that the studies cited either considered the effects of cleaning agents or were conducted in real-world circumstances where cleaning agents might have been deployed. I'm questioning my assumption now, though. Regardless, it remains we have seen VERY few transmission incidents involving surfaces.
I think that all of these studies take into account human behaviors relatively well, because they are all at their heart based on real-world measurement of how much SARS-CoV-2 ends up deposited on various surfaces. So that endpoint, as measured, is going to be affected by all of the mitigation strategies in place to some degree. For example, mask-wearing will be relevant to surface transmission, because it will reduce the amount of output virus from an infected person. Reducing the output virus will reduce how much of it becomes deposited on surfaces.
It's a complex scenario, but ultimately, the proof of the low impact of fomite transmission comes out of the relatively low numbers of definitive fomite-transmitted cases that we have encountered in the wild. SARS-CoV-2 has been out in many environments, and you would think that by now we would have, at the very least, thousands of reports of cases where someone walked into a room that had been occupied by a COVID-19 patient an hour earlier, never had contact with that patient, and then became ill. We don't have thousands of such reports, which says to me that fomite (surface) transmission must be exceptionally rare.
The risk level of "less than 1 in 10,000" (it was estimated to range from 1 in 10,000 to 1 in 1,000,000 by the cited paper) is based on reconciling the above fact with information already known about how much virus deposits on surfaces. It's not a rigorous scientific fact, but rather a model based on two observations that have been made. We know that fomite transmission is rare, we know how much virus is likely to be deposited on surfaces, and in trying to reconcile those two things, the authors of the main cited paper came to their reported risk model.
Like most models, it's inadequate and vague, I have to agree, but I think it does help us to prioritize risk. All models are wrong, but some are useful--as the old saying in statistics goes.
Yeah, I never thought that was a thing. I don't think I encountered anyone professionally involved in ID who thought that was a really serious risk, or at least no one who thought it was so serious that you should take abnormal precautions. The one time I saw something about COVID-19 food safety, it was full of recommendations that were just things you should always do with food anyway, like not eat it if someone who was sick coughed into it.
That CDC brief on surface transmission is annoying vague about certain things.
Note about your analysis: that's 1 in 10,000 *per surface touched*. If you touch 100 contaminated surfaces per day, the risk would appear to rise to 1% per day! Very few people eat 100 eggs per day. (I know of one toxicologist who did it at least once, but that guy used to do some weird stuff.)
Also, what's a "surface" for this purpose? Each door handle, each light switch, each chair back? You could reach 100 easily, if you're in an area with high incidence of infection.
OTOH, it actually says "less than" 1 in 10,000, so ... did I mention it's annoying vague?
Then again, maybe it doesn't take handwashing into account? It says things like, " Hand hygiene is a barrier to fomite transmission and has been associated with lower risk of infection." and "The risk of fomite transmission can be reduced by wearing masks consistently and correctly, practicing hand hygiene, cleaning, and taking other measures to maintain healthy facilities." It doesn't (as you wrote) make clear if its risk assessment does, or does not, include hand hygiene, but I have to think not. If it did, then would this not imply that it also takes into account mask wearing (How is that relevant to surface transmission), cleaning, and "other measures"? And isn't "other measures" ... annoying vague?
I do think it's relatively vague, yeah, but all of this is an approximation. We're never going to have great models for anything in this situation. Let's keep in mind, of course, that even my egg example is approximation based on expectation values, since really, given how randomness works, you'd need to go through about three times that many eggs to be almost guaranteed to get one contaminated egg. There's always some chance that you don't encounter the event within the expected number of iterations; anyone who has flipped a coin twice and gotten the same result has experienced a failure of expectation values to represent reality.
When I said I think it takes into account hand hygiene, I was basing it on the fact that the studies cited either considered the effects of cleaning agents or were conducted in real-world circumstances where cleaning agents might have been deployed. I'm questioning my assumption now, though. Regardless, it remains we have seen VERY few transmission incidents involving surfaces.
I think that all of these studies take into account human behaviors relatively well, because they are all at their heart based on real-world measurement of how much SARS-CoV-2 ends up deposited on various surfaces. So that endpoint, as measured, is going to be affected by all of the mitigation strategies in place to some degree. For example, mask-wearing will be relevant to surface transmission, because it will reduce the amount of output virus from an infected person. Reducing the output virus will reduce how much of it becomes deposited on surfaces.
It's a complex scenario, but ultimately, the proof of the low impact of fomite transmission comes out of the relatively low numbers of definitive fomite-transmitted cases that we have encountered in the wild. SARS-CoV-2 has been out in many environments, and you would think that by now we would have, at the very least, thousands of reports of cases where someone walked into a room that had been occupied by a COVID-19 patient an hour earlier, never had contact with that patient, and then became ill. We don't have thousands of such reports, which says to me that fomite (surface) transmission must be exceptionally rare.
The risk level of "less than 1 in 10,000" (it was estimated to range from 1 in 10,000 to 1 in 1,000,000 by the cited paper) is based on reconciling the above fact with information already known about how much virus deposits on surfaces. It's not a rigorous scientific fact, but rather a model based on two observations that have been made. We know that fomite transmission is rare, we know how much virus is likely to be deposited on surfaces, and in trying to reconcile those two things, the authors of the main cited paper came to their reported risk model.
Like most models, it's inadequate and vague, I have to agree, but I think it does help us to prioritize risk. All models are wrong, but some are useful--as the old saying in statistics goes.
It occurs to me that this article doesn't even mention foodborne transmission, which I assume is now acknowledged to not be a thing.
Yeah, I never thought that was a thing. I don't think I encountered anyone professionally involved in ID who thought that was a really serious risk, or at least no one who thought it was so serious that you should take abnormal precautions. The one time I saw something about COVID-19 food safety, it was full of recommendations that were just things you should always do with food anyway, like not eat it if someone who was sick coughed into it.