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Much has happened in the past year, so you can forgive yourself for not having a clear memory of some of the top concerns at the start of the pandemic.
However, if you think back to the start of the pandemic, one of the major concerns was the role surfaces played in transmitting the virus.
As an epidemiologist, I remember spending countless hours responding to media inquiries answering questions about whether we should wash the outside of cans or disinfect our mail.
I also remember seeing teams of people walking the streets all day long, wiping down poles and cleaning public benches.
But what is the proof Actually say about surface transmission more than 12 months after the start of this pandemic?
Before we get into that, we need to define the question we are asking ourselves. The key question is not whether surface transmission is possible or if it can occur in the real world – it almost certainly is.
The real question is: what is the extent of the role of surface contact in the transmission of the virus? In other words, what is the probability of catching COVID via a surface, as opposed to other methods of transmission?
There is little evidence that surface transmission is a common way of spreading the coronavirus. The main way it is spread is through the air, either through larger droplets on close contact, or through smaller droplets called aerosols. By the way, the relative role of these two pathways in transmission is probably a much more interesting and important question to clarify from a public health perspective.
One of the best comments on COVID surface transmission has been published in the journal Lancet Infectious Diseases in July 2020 by Emanuel Goldman, professor of microbiology in the United States.
As he described, one of the driving forces behind the exaggerated perception of the risk of surface transmission was the publication of a number of studies showing that SARS-CoV-2 viral particles could be detected for long periods of time. long periods on various surfaces.
You probably saw these studies because they received huge publicity around the world and I remember doing a lot of interviews where I had to explain what these results really meant.
As I explained at the time, these studies could not be generalized to the real world, and in some cases the press releases that came with them tended to overestimate the importance of these findings.
The key problem is that, as a general rule, the time it takes for a population of microorganisms to die is directly proportional to the size of that population. This means that the greater the amount of virus deposited on a surface, the longer you will find viable virus particles on that surface.
So in terms of designing experiments that are relevant to public health, one of the most important variables in these studies is the amount of virus deposited on a surface – and how close that is to what would happen in the real world.
If you understand this, it becomes evident that a number of these virus survival studies have stacked the odds of detecting a viable virus by depositing large amounts of virus on areas far larger than one could reasonably expect. expect to find in the real world. Additionally, some of these studies personalized conditions that would prolong the life of viral particles, such as humidity adjustment and exclusion of natural light.
While there is nothing wrong with the science here, it was the real world relevance and interpretation that was sometimes wrong. Of note, other studies that more closely replicated real-world scenarios found less impressive survival times for three other human coronaviruses (including SARS).
Importantly, we are relying on indirect evidence to assess the role of surface transmission for the coronavirus. In other words, you can’t actually do an ethical science experiment that confirms the role that surface transmission plays because you would have to deliberately infect people. Although this is a seemingly simple question, it is surprisingly difficult to determine the relative importance of the different routes of transmission of this virus.
What we need to do instead is look at all the evidence we have and see what it tells us, including case studies describing transmission events. And if we do that, there isn’t much to argue that surface transmission is of major importance in the spread of COVID.
We need to put into perspective the risks of exposure to SARS-CoV-2 through the different modes of transmission, so that we focus our energy and limited resources on the right things.
This is not to say that surface transmission is not possible and safe in some situations, or that we should ignore it altogether. But we must recognize that the threat posed by surface transmission is relatively low.
We can therefore mitigate this relatively low risk by continuing to focus on hand hygiene and ensuring that cleaning protocols are more aligned with the risk of surface transmission.
By doing this, we can potentially save millions of dollars spent on obsessive cleaning practices. These probably provide little or no benefit and are done only because they are easy to do and reassure us to do something, thus relieving some of our anxieties.
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