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Stability of SARS-CoV-2 in different environmental conditions

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  • Stability of SARS-CoV-2 in different environmental conditions

    To the Editor,

    We previously reported the detection of SARS-CoV-2 in different clinical samples1 . This virus can be detected on different surfaces in a contaminated site2 . Here, we report the stability of SARS-CoV-2 in different environmental conditions. We first determined the stability of SARS-CoV-2 at different temperatures. SARS-CoV-2 in virus transport medium (VTM; final concentration: ∼6.8 log TCID50/mL) was incubated for up to 14 days and then tested for its infectivity (Table A).

    The virus is highly stable at 4°C, but sensitive to heat. At 4°C, there was only ∼0.7-log unit reduction of infectious titre on Day 14. With the incubation temperature being increased to 70°C, the time for virus inactivation was reduced to 5 minutes. We further investigated the stability of this virus on different surfaces. In brief, a 5-µL droplet of virus culture (∼7.8 Log unit of TCID50/mL) was pipetted on a surface (Table B; ∼1cm2 per piece) and left at room temperature (22°C; Relative humidity: ∼65%).

    The inoculated objects retrieved at desired time points were immediately soaked with 200 µL of VTM for 30 minutes to elute the virus. No infectious virus could be recovered from printing and tissue papers after a 3-hour incubation, whereas no infectious virus could be detected from treated wood and cloth on Day 2. By contrast, SARS-CoV-2 was more stable on smooth surfaces.

    No infectious virus could be detected from treated smooth surfaces on Day 4 (glass and banknote) or Day 7 (stainless steel and plastic). Strikingly, a significant level of infectious virus could still be detected on the outer layer of a surgical mask on Day 7 (∼0.1% of the original inoculum). Interestingly, a biphasic decay of infectious SARS-CoV-2 could be found from samples recovered from these smooth surfaces (Appendix).

    Representative negative samples were tested positive by RT-PCR3 (N=39; data not shown), demonstrating that non-infectious viruses could be recovered by the eluents. We also tested the virucidal effects of disinfectants by adding 15 µL of SARS-CoV-2 culture (∼7.8 Log unit of TCID50/mL) to 135 µL of various disinfectants at working concentration (Table C). With the exception of a 5-min incubation with hand soap, no infectious virus could be detected after a 5-minute incubation at room temperature.

    In addition, we also found that It is made available under a CC-BY-NC-ND 4.0 International license . author/funder, who has granted medRxiv a license to display the preprint in perpetuity. medRxiv preprint doi: https://doi.org/10.1101/2020.03.15.20036673.

    The copyright holder for this preprint (which was not peer-reviewed) is the SARS-CoV-2 is extremely stable in a wide-range of pH values at room temperature (pH3-10; Table D) Overall, SARS-CoV-2 can be highly stable in a favourable environment4 , but it is also susceptible to standard disinfection methods.

    “Addressing chronic disease is an issue of human rights – that must be our call to arms"
    Richard Horton, Editor-in-Chief The Lancet

    ~~~~ Twitter:@GertvanderHoek ~~~ GertvanderHoek@gmail.com ~~~

  • #2
    Tweets from the author:

    This preprint looked at the effect of temperature. Bad news: in virus transport medium, infectious titer (amount of infectious virus), was pretty stable, with <1 log reduction over 14 days at 4 degrees C. (4 C is the temperature of your refrigerator)
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    Dr. Angela Rasmussen

    @angie_rasmussen
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    However, it confirmed that heat can inactivate the virus. When temperature was increased to 70 C, the virus was inactivated in 5 minutes. This has implications for disinfection methods and may be especially relevant for reusing PPE.
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    Dr. Angela Rasmussen

    @angie_rasmussen
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    In this study, the ambient conditions were room temp (22 C) with 65% relative humidity (that's fairly high). Under these conditions, no infectious virus on printer or tissue paper could be recovered after 3 h. On treated wood or cloth, no virus could be recovered after 2 days.
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    Dr. Angela Rasmussen

    @angie_rasmussen
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    The authors assert that surface textures are important. Under these conditions, no infectious virus could be recovered from glass or paper currency after day 4 or plastic/stainless steel after day 7.
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    Dr. Angela Rasmussen

    @angie_rasmussen
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    (Aside: not sure if the bank notes tested were HKDs fresh from the mint. I wouldn't go so far to say that the USDs in my wallet are "smooth" surfaces. This could have an impact on the risk presented by handling money, but it's hard to say what that is. Keep washing those hands!)
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    Dr. Angela Rasmussen

    @angie_rasmussen
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    For all the mask-lovers out there: 0.1% of the inoculum could be detected on a surgical mask after a week. The inoculum was ~600K TCID50/mL (units of the dose required to kill 50% of the Vero E6 cells in a tissue culture dish per milliliter). That's 600 TCID50/mL.

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    Dr. Angela Rasmussen

    @angie_rasmussen
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    We don't know what the minimum infectious dose is for people (the minimum # of infectious units needed to infect a human), but 600 TCID50/mL after a week suggests that infectious virus can at least persist on surgical masks for a week. Thus masks are a potential exposure risk.
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    Dr. Angela Rasmussen

    @angie_rasmussen
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    The virus also was stable over a broad range of pH, meaning that it's more tolerant to both acidic (low pH) and basic (high pH) conditions. The good news is that they also tested disinfectants, which were all very effective in inactivating virus in short periods of time.
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    Dr. Angela Rasmussen

    @angie_rasmussen
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    A note of caution: this is a preprint so it hasn't undergone peer review. However, it is from Malik Peiris and Leo Poon's groups, and they are highly regarded virologists who were the first to isolate SARS classic and have extensive experience studying coronaviruses.
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    Dr. Angela Rasmussen

    @angie_rasmussen
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    The take-home is that SARS-CoV-2 is stable on many surfaces, including surgical masks, for days under specific environmental (temp/humidity) conditions. The virus is sensitive to changes in temperature and can be inactivated rapidly by disinfectants, just like other coronaviruses
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    Victoria Moore
    @PlanetVictoria
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    Als antwoord op
    @angie_rasmussen
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    @DocBazac
    Which disinfectants were effective?
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    Dr. Angela Rasmussen

    @angie_rasmussen
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    Bleach, povidone/iodine, 70% ethanol, chloroxylenol, chlorhexidine, benzalkonium chloride, and hand soap. Hand soap took longer (still virus after 5 minutes), but inactivated virus after 10 min. This doesn't mean hand soap doesn't work, because washing hands also rinses virus off
    “Another pre-print is out looking at #SARSCoV2 #HCoV19 #COVID19 #coronavirus stability in different environmental conditions. (Thanks, @DocBazac, for the tip!) https://t.co/rhxscH4VMU”
    “Addressing chronic disease is an issue of human rights – that must be our call to arms"
    Richard Horton, Editor-in-Chief The Lancet

    ~~~~ Twitter:@GertvanderHoek ~~~ GertvanderHoek@gmail.com ~~~

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