13 October 2020

Thoughts regarding the survival of coronavirus

Broadcast, print, and electronic media have carried quite a few reports recently regarding how long coronavirus will survive on various surfaces (paper mail, food packaging, doorknobs etc).  I have no special expertise in virology or viral biology, but my gut impression is that coronavirus primarily spreads like other respiratory viruses, via droplet nuclei and aerosolized particles, and that transmission by contact with fomites (physical objects) is a relatively unimportant factor in its epidemiology.

I no longer have access to the primary data on most medical articles, relying like everyone else on second- or third-hand interpretations of what a study discovered.  But yesterday I decided to chase one article down.  A report in LiveScience was titled "Coronavirus can survive on skin for 9 hours."  The study was published in Clinical Infectious Diseases, which I understand to be a reputable journal, and the original data is available in pdf form.

The image embedded at the top is Figure 1 from the article - a composite illustration of the methodology and the results.  I don't question the findings per se, but I have some concerns re the extrapolation to real life.  Note that the bar graph shows a decline in detectable virus (FFU=focus forming units, equivalent to colony forming units in bacterial studies) from about 10^5 at time zero to 10^2 one hour later.  Clearly the virus did survive that interval, but it incurred a 3-log-power decline in that time.

So how does this translate to real-life risk?  I don't know what constitutes a normal viral inoculum.  How many FFU are there in an aerosolized droplet?  On an infected person's hand when they touch a doorknob or someone else's hand?  The authors seems to acknowledge this in their discussion: "... since not only the virus stability but also the infectious dose and transmission route may greatly affect the risk of contact-transmission, future research needs to focus on factors other than virus stability."

After three decades spent writing and reviewing research grants and manuscripts for publication, I know that the main conclusion of most research is always that more research needs to be done.  Some of it may have been done already; if any readers know of relevant results, I'd be delighted to see the info in the comments section of his post.


  1. The problem in all of this is that many people think that getting the/a virus is a binary game. You get it or you don't. Like flipping a coin. But it's not like that. It's a probability game. Like playing the lottery.

    So the question is: How many times do you have to play before you "win" the lottery? There is no straight answer to this question. You can win by participating once, however unlikely. Most people never win, despite playing all their lives. And some people win anyway, because they play.

    So, if you don't want to get ill, the goal becomes to not play the lottery. This is where every individual has an influence. You don't play:

    * when you keep your distance
    * when you reduce human interaction, see less people
    * when you wash your hands
    * when you wear a face mask
    * etc.

    It would be really helpful if the public at large would not focus on the lack of logic in specific rules that governments put in place to get people to play the lottery less, and would focus more on not playing the freaking lottery.

    And please, share sad stories with your friends and family about COVID cases in your environment.

    I only got my parents to because serious about sticking to the rules, when a couple their age down the street died. Both. Before the test result came back. While they were following the rules "pretty well". Stayed at home. Let their kids bring the groceries. Their mistake? They hugged their daughter once, during the grocery drop-off. And their daughter was an asymptomatic carrier. They "won" the lottery upon playing once. And their daughter now has to live the rest of her live knowing that she "killed" her parents, despite not knowing she was infected.

    This virus is serious. By now, everybody know of someone who suffered or died. You don't want to be that person. Or their family.

    So don't play the damn lottery. You know the house always wins.

    1. I agree with this wholeheartedly. I haven't seen my father since March, I've only seen my mother from 6 feet away in a mask. My kids miss their grandparents terribly, and as hard as it is, I know it would be immeasurably harder for them to live with the idea that they were the cause of someone's death.
      That is the reason I always wear my mask when I go out, even when no one else does. I love my community and am doing my best to keep them all safe. Sometimes it feels like I'm swimming against the tide, but it's literally all I can do.

  2. Riddell et al. Virol J (2020) 17:145 https://doi.org/10.1186/s12985-020-01418-7
    The effect of temperature on persistence of SARS-CoV-2 on common surfacesShane Riddell*, Sarah Goldie, Andrew Hill, Debbie Eagles and Trevor W. Drew


    Don't know if this answers any questions

    1. This is a fairly relevant paragraph from your link:

      Tis study utilised a virus concentration of 4.97×10^7/
      mL diluted into a standard solution which mimics body
      fuid composition (fnal concentration of 3.38×105
      /10 ┬ÁL inoculum), which equates to a cycle threshold (CT) value
      of 14.2, 14.0 and 14.8 for N gene, E gene and RdRp gene
      real time RT-PCR, respectively (unpublished data). Previous studies have shown some patients with high viral loads have recorded CT values of between 13 and 15 [19–21]. van Doremalen et al. [5] described their test material(105TCID50/mL) as having a CT of 20–22, which compared similarly to CTs reported from clinical patients [5,22]. While the titre of virus utilised in this study is high it represents a plausible amount of virus that may bedeposited on a surface.

  3. I was under the impression that most viruses, even aerosol ones, were transmitted mainly nose picking.


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