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There are studies on the persistence of the SARS-CoV-2 virus on surfaces. These studies aim to find out how long a surface remains infectious to humans.

As far as I understand, it is not determined experimentally how long a surface remains infectious, or whether significant numbers of the viruses are present. Also, these tests do not identify the complete RNA of the virus, instead detecting the presence of fragments of viral RNA.

Now, some theorize that viruses in a droplet become inactive when the droplet evaporates. I think the expected effect depends only on the virus being dry, but maybe also the process of drying and the liquid.

That can't be right, because it would mean that a surface a person has sneezed on would be harmless after only a few minutes, and that's wrong.

We think surfaces are infectious for practical purposes. But is that established experimentally? Or do we only detect RNA fragments, and use this to infer the presence of viruses?

If so, this may imply infections attributed to touching dry surfaces are in fact caused by direct human interaction, or by touching wet surfaces. That problem could be undetected because the time between surface contact and symptoms is so long. Also, studies regarding the virus did not have much time until now.

Is it possible that droplet evaporation destroys SARS-CoV-2? Is it probable for practical purposes?

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    I suggest you read the papers that answer all these questions
    – Graham Chiu
    Commented Apr 1, 2020 at 8:05

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The work you’re likely referring to is Neeltje van Doremalen et al. (2020), which evaluates the surface stability of viable SARS-CoV-2 virus. In this experiment viable virus was found to survive for three days on plastic and stainless steel surfaces. This result has been widely reported in news media. You can read the methods appendix to understand exactly how viability is determined. See: https://www.nejm.org/doi/full/10.1056/NEJMc2004973

Fragments of viral RNA, which pose no risk of infection, remain detectable for much longer — at least 17 days per Leah F. Moriarty et al. (2020). See: https://www.cdc.gov/mmwr/volumes/69/wr/mm6912e3.htm?s_cid=mm6912e3_w

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  • My previous vague assumptions was something like "a few days" for a surface staying infectious, and I had heard of longer times, but never specifying the kind of test was used.I suspected it was often a PCR based test and looking for partial viruses also. Basically, I did not have that misunderstanding, and the second and third paragraph are a perfect answer. Thanks!
    – Volker Siegel
    Commented Apr 11, 2020 at 12:58
  • I was reacting to “It would mean that a surface a person has sneezed on would be harmless after only a few minutes,” which is a dangerous speculation to make publicly right now. I’d remove my first line if I had enough karma to edit because it doesn’t add anything to the answer — sorry for being rude.
    – goodside
    Commented Apr 11, 2020 at 14:48
  • I see what you mean - that sentence stands out, without obvious context, and is at least ambiguous. What I intended to say was: "The previous paragraph would imply that this impossible thing would happen, so it can not be true. " Now, I assumed "harmless after only a few minutes" is certainly not true. But that is not obvious. I'll clarify it. You were not rude, and thanks for pointing it out!
    – Volker Siegel
    Commented Apr 11, 2020 at 21:55
  • I understand better what you’re asking now and will expand my answer later. I’ve made some edits to your question for grammar and clarity.
    – goodside
    Commented Apr 11, 2020 at 23:05
  • Thank you for your edits!
    – Volker Siegel
    Commented Apr 15, 2020 at 23:56

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