I’ve been hearing a lot of people talking about how #coronavirus can survive on hard surfaces for DAYS, which I feel has created a lot of unnecessary fearmongering regarding how the virus spreads.

The main reason people say that is because of an article in the New England Journal of Medicine however, since nobody read the actual article (and only read news stories about it), there is a wide gap between the data and what people are saying.

First, the study showed that on surfaces such as copper, cardboard, stainless steel, and plastic, viruses that were capable of infecting cells could be found at up to 8 hours on copper, 24 hours on cardboard, and 72 hours on stainless steel and plastic. If you look at the graph below, the red dots = current SARS coronavirus and blue dots = SARS from 2002. Any dot above the dashed horizontal line means that there were infectious virus.

Screen Shot 2020-03-21 at 9.11.03 AM

That’s horrifying news you say? Viruses can live on surfaces for DAYS AND DAYS! OMG! Well, the issue with that is you have to pay attention to the Y-axis, which says “Titer (TCID50/ml of medium)” What the Y-axis tells you is HOW MANY infectious virus particles were able to be detected at a given time.

Why is that important? Because different viruses have different INFECTIOUS DOSES (essentially the number of virus particles you need to be infected with to actually get sick). While we don’t really know the infectious dose of the current SARS coronavirus the 2002 SARS virus may have had an infectious dose of ~16-160 viruses required for spreading SARS.

Assuming the current SARS coronavirus is anything like what was reported for 2002 SARS, we can ignore any of the dots below 101 (ie 10), which is below the low range (16) of virus particles required for spreading.

Again, the high end of the infectious dose range for 2002 SARS was 160 virus particles. Therefore, some patients required a lot more (>100) virus particles to be infected with SARS, and the dots below 102 (ie, 100) become less relevant for infection.

Looking back at the graph, if you draw a line at number of virus particles relevant for infection in most people (see teal line at 102), the current SARS coronavirus survives 1 hour on copper, 4 hours on cardboard, 8-24 hours on stainless steel, and 24 hours on plastic.

Screen Shot 2020-03-21 at 2.56.31 PM

You may be thinking: A whole day surviving on plastic is pretty bad! Well, this data assumes ideal laboratory settings (69.8-73.4° F and 40% relative humidity – which may only apply to Hawaii?), and the fact that surfaces are not wiped, which is unlikely these days.

I’m not trying to say you can’t get the current SARS #coronavirus from touching a surface – you definitely can. But let’s not excessively spread panic when we don’t need it.

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