It’s truly amazing how much we know about COVID-19 and the virus that causes it (SARS-CoV-2), considering it was only identified a few months ago. However, there are still lots of basic things we don’t understand (yet).
One important question is whether the environment is a significant source of infection. When people breathe, cough, talk or touch surfaces, they can contaminate them with the virus – that’s obvious. But are those surfaces then important source of infection to others, an uncommon source, or not significant at all? Some people have stuck to the “There’s no evidence of…” line, but we need to bear in mind that “absence of evidence” isn’t the same as “evidence of absence.”
So, what is the evidence for the environment as a source of SARS-CoV-2 exposure?
One thing that is to our advantage here is that coronaviruses, including this one, are enveloped viruses. That means they have a fatty external coating that is relatively easy to disrupt. As a result, enveloped viruses tend to be pretty wimpy once outside their host. They generally don’t survive well in the environment (though there are exceptions) and they tend to be easy to kill with disinfectants, compared to non-enveloped viruses (like parvovirus, for example) that can live for a long time in the environment and be resistant to many disinfectants. So, long term survival of SARS-CoV-2 outside a host isn’t expected. However, the question remains whether short term environmental survival could be a problem.
A paper in the New England Journal of Medicine (Doremalen et al.) looked at the stability of the COVID-19 virus (and its cousin, the original SARS virus) in aerosols and on different surfaces. Some key points were:
- The virus remained viable in aerosols for up to 3 hours (which is as long as they tested). The infection load decreased but not substantially. (This isn’t the topic of this post, but this result has raised a lot of concern in the medical field.)
- SARS-CoV-2 survived better on plastic and stainless steel compared to copper and cardboard. While the viral loads decreased, viable virus was still present on plastic after 72 hours and on stainless steel for 48 hours.
- The estimated half live on steel and plastic were 5.6 and 6.8 hours, respectively. That is how long it takes for 50% of the deposited virus to die. So, after 12 hours, ~25% would be left, and so on.
The researchers concluded, “Our results indicate that aerosol and fomite transmission of SARS-CoV-2 is plausible, since the virus can remain viable and infectious in aerosols for hours and on surfaces up to days (depending on the inoculum shed). These findings echo those with SARS-CoV-1, in which these forms of transmission were associated with nosocomial spread and super-spreading events, and they provide information for pandemic mitigation efforts.“
We don’t know whether the environment is a problem, but we should assume that can be until proven otherwise. This also relates to animals as environmental sources. We should assume that SARS-CoV-2 deposited on a pet’s haircoat by an infected owner can survive for at least a few hours, so we’re accounting for that in our handling guidelines.
Wash your hands, stay home if you’re sick (or even if you’re not, if you can), cough/sneeze into your elbow, and practice good cleaning and disinfection. The basics of infection control are pretty… well… basic, but they are the mainstay of prevention.