A lot has happened over the past year, and you can be forgiven for not having a clear memory of what the biggest concerns were at the beginning of the pandemic.
However, if you think back to the beginning of the pandemic, the role that surfaces played in the transmission of the virus was one of the biggest concerns.
As an epidemiologist, I remember spending countless hours responding to media requests to answer questions about whether we should wash the outside of lunch boxes or disinfect our mail.
I also remember that at all times I saw teams of people walking around in the streets wiping poles and cleaning public banks.
But what does the evidence do? actually say about the transfer of the surface more than 12 months after this pandemic?
Before we address this, we need to define the question we are asking. The key question is not whether the transfer of the surface is possible, or whether it can take place in the real world – it can be almost certain.
The real question is: what is the extent of the role of surface contact in the transmission of the virus? That is, what is the probability of capturing COVID via a surface, as opposed to other transmission methods?
There is little evidence that surface transfer is a common way the coronavirus is spread. The main way it is distributed is through the air, either through larger droplets via close contact, or through smaller droplets called aerosols. As a side issue, the relative role that these two pathways play in transmission is likely to be a much more interesting and important question to explain from a public health perspective.
One of the best comments on COVID Surface Transmission was published in the magazine Lancet Infectious Diseases in July 2020 by Emanuel Goldman, a professor of microbiology of the United States.
As he describes, the publication of a number of studies indicating that SARS-CoV-2 viral particles could be detected on different surfaces for long periods of time was one of the drivers for the exaggerated perception of the risk of surface transfer.
You have probably seen these studies because they have received enormous publicity worldwide and I remember conducting numerous interviews in which I had to explain what these findings actually mean.
As I explained at the time, these studies could not be generalized to the real world, and in some cases, the media statements that accompanied them overestimated the importance of these findings.
The most important issue is that the duration for the population of microorganisms as a general principle is directly proportional to the size of the population. This means the greater the amount of virus deposited on a surface, the longer you will find viable viral particles on the surface.
Thus, in terms of designing experiments relevant to public health, one of the most important variables in these studies is amount virus laid on a surface – and the extent to which it approaches what would happen in the real world.
If you understand this, it appears that a number of these virus survival studies have increased the chances of detecting viable viruses by depositing large amounts of viruses on surfaces that are far more than would reasonably be expected in the real world. What’s more, some of these studies have adapted conditions that would extend the life of viral particles, such as adjusting the humidity and excluding natural light.
Although there was nothing wrong with science here, it was sometimes the right relevance and interpretation. It is noteworthy that other studies that closely replicate the actual world scenarios have found less impressive survival times for three other human coronaviruses (SARS included).
It is important to note that we rely on indirect evidence to assess the role of surface transfer for the coronavirus. That is, you can not actually do an ethical scientific experiment that confirms the role of surface transfer because you have to deliberately infect humans. Despite the fact that it is such a seemingly simple question, it is surprisingly difficult to determine the relative importance of the different transmission routes for 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, there is not much to support the transfer of the surface area of great importance in the spread of COVID.
We need to put the risks of exposure to SARS-CoV-2 into perspective via the different transmission methods, so our limited energy and resources focus on the right things.
This does not mean that the transfer of the surface is not possible and that in certain situations it poses no risk, or that we should disregard it completely. But we must admit that the transfer of the surface is relatively small.
We can therefore mitigate this relatively small risk by continuing to focus on hand hygiene and ensuring that cleaning protocols are more in line with the risk of surface transfer.
By doing so, we can save millions of dollars spent on obsessive cleaning practices. It probably offers little or no benefit and is only done because it is easy to do and gives the assurance of doing something, thus alleviating some of our worries.