Aerosol and surface stability of SARS-CoV-2 compared to SARS-CoV-1 – ABOUT MAG 2020

For the publisher:

A new human coronavirus that is now called severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (formerly called HCoV-19) emerged in Wuhan, China in late 2019 and is now causing a pandemic.1 We analyzed the aerosol and surface stability of SARS-CoV-2 and compared it with SARS-CoV-1, the most closely related human coronavirus.2

We assessed the stability of SARS-CoV-2 and SARS-CoV-1 in aerosols and on various surfaces and estimated their decay rates using a Bayesian regression model (see the Methods section in Supplementary appendix, available with the full text of this letter at NEJM.org). SARS-CoV-2 nCoV-WA1-2020 (MN985325.1) and SARS-CoV-1 Tor2 (AY274119.3) were the strains used. Aerosols (<5 μm) containing SARS-CoV-2 (105.25 Infectious dose of 50% of tissue culture[TCID[TCID[TCID[TCID50.]per milliliter) or SARS-CoV-1 (106.75-7.00 TCID50. per milliliter) were generated using a Collison nebulizer with three jets and fed in a Goldberg drum to create an aerosol environment. The inoculum resulted in cycle threshold values ​​between 20 and 22, similar to those observed in samples obtained from the upper and lower respiratory tract in humans.

Our data consisted of 10 experimental conditions involving two viruses (SARS-CoV-2 and SARS-CoV-1) in five environmental conditions (aerosols, plastic, stainless steel, copper and cardboard). All experimental measurements are reported as averages over three repetitions.

Figure 1. Figure 1. Viability of SARS-CoV-1 and SARS-CoV-2 in aerosols and on various surfaces.

As shown in Panel A, the titer of the viable aerosol virus is expressed in 50% of the infectious dose of tissue culture (TCID50.) per liter of air. The viruses were applied to copper, cardboard, stainless steel and plastic, maintained at 21 to 23 ° C and 40% relative humidity for 7 days. The title of the viable virus is expressed as TCID50. per milliliter of collection medium. All samples were quantified by endpoint titration in Vero E6 cells. The graphs show the means and standard errors (𝙸 bars) in three repetitions. As shown in Panel B, the regression graphs indicate the expected deterioration of the virus titer over time; the title is plotted on a logarithmic scale. The dots show the measured titles and are slightly unstable (that is, their horizontal positions are modified by a small random amount to reduce overlap) along the time axis to avoid plotting. The lines are drawn randomly from the joint posterior distribution of the exponential decay rate (slope negative) and intercept (initial virus titer) to show the range of possible decay patterns for each experimental condition. There were 150 lines per panel, including 50 lines for each replica plotted. As shown in Panel C, violin plots indicate further distribution for the viable virus half-life, based on the estimated exponential decay rates of the virus titer. The dots indicate the later median estimates and the black lines indicate a credible 95% range. The experimental conditions are ordered according to the median posterior half-life of SARS-CoV-2. The dashed lines indicate the detection limit, which was 3.33 × 100.5 TCID50. per liter of air for aerosols, 100.5 TCID50. per milliliter of medium for plastic, steel and cardboard and 101.5 TCID50. per milliliter of medium for copper.

SARS-CoV-2 remained viable in aerosols for the duration of the experiment (3 hours), with a 10% reduction in infectious titer3.5 to 102.7 TCID50. per liter of air. This reduction was similar to that observed with SARS-CoV-1, 104.3. to 103.5 TCID50. per milliliter (Figure 1A)

SARS-CoV-2 was more stable on plastic and stainless steel than on copper and cardboard, and the viable virus was detected up to 72 hours after application on these surfaces (Figure 1A), although the virus titer has been quite low (from 103.7 to 100.6 TCID50. per milliliter of medium after 72 hours in plastic and from 103.7 to 100.6 TCID50. per milliliter after 48 hours in stainless steel). The stability kinetics of SARS-CoV-1 was similar (from 103.4. to 100.7 TCID50. per milliliter after 72 hours in plastic and from 103.6. to 100.6 TCID50. per milliliter after 48 hours in stainless steel). In copper, no viable SARS-CoV-2 was measured after 4 hours and no viable SARS-CoV-1 was measured after 8 hours. On cardboard, no viable SARS-CoV-2 was measured after 24 hours and no viable SARS-CoV-1 was measured after 8 hours (Figure 1A)

Both viruses had an exponential deterioration in virus titer under all experimental conditions, as indicated by a linear decrease in the log10TCID50. per liter of air or milliliter of a half over time (Figure 1B) The SARS-CoV-2 and SARS-CoV-1 half-lives were similar in aerosols, with median estimates of approximately 1.1 to 1.2 hours and credible 95% intervals from 0.64 to 2.64 for SARS-CoV-2 and 0.78 to 2.43 for aerosols. SARS-CoV-1 (Figure 1Cand Table S1 in Supplementary appendix) The half-lives of the two viruses were also similar for copper. On cardboard, the half-life of SARS-CoV-2 was greater than that of SARS-CoV-1. The longest viability of the two viruses was stainless steel and plastic; the estimated average half-life of SARS-CoV-2 was approximately 5.6 hours for stainless steel and 6.8 hours for plastic (Figure 1C) The estimated differences in the half-lives of the two viruses were small, except for the cardboard ones (Figure 1C) The individual replicated data was noticeably “noisier” (that is, there was more variation in the experiment, resulting in a larger standard error) for cardboard than for other surfaces (Figs S1 to S5), so we advise caution when interpreting this result.

We found that the stability of SARS-CoV-2 was similar to that of SARS-CoV-1 under the experimental circumstances tested. This indicates that the differences in the epidemiological characteristics of these viruses are likely to arise from other factors, including high viral loads in the upper respiratory tract and the potential for people infected with SARS-CoV-2 to eliminate and transmit the virus while asymptomatic.3.4 Our results indicate that the transmission of SARS-CoV-2 aerosol and fomite is plausible, since the virus can remain viable and infectious in aerosols for hours and on surfaces for days (depending on the inoculum released). These findings echo those with SARS-CoV-1, in which these forms of transmission have been associated with hospital spread and over-spread events,5 and provide information for pandemic mitigation efforts.

Neeltje van Doremalen, Ph.D.
Trenton Bushmaker, B.Sc.
National Institute of Allergy and Infectious Diseases, Hamilton, MT

Dylan H. Morris, M. Phil.
Princeton University, Princeton, NJ

Myndi G. Holbrook, B.Sc.
National Institute of Allergy and Infectious Diseases, Hamilton, MT

Amandine Gamble, Ph.D.
University of California, Los Angeles, Los Angeles, CA

Brandi N. Williamson, M.P.H.
National Institute of Allergy and Infectious Diseases, Hamilton, MT

Azaibi Tamin, Ph.D.
Jennifer L. Harcourt, Ph.D.
Natalie J. Thornburg, Ph.D.
Susan I. Gerber, M.D.
Centers for Disease Control and Prevention, Atlanta, GA

James O. Lloyd-Smith, Ph.D.
University of California, Los Angeles, Los Angeles, CA, Bethesda, MD

Emmie de Wit, Ph.D.
Vincent J. Munster, Ph.D.
National Institute of Allergy and Infectious Diseases, Hamilton, MT

Supported by Intramural Research Program of the National Institute of Allergy and Infectious Diseases, National Institutes of Health and Advanced Defense Research Projects Agency contracts (DARPA PREEMPT N ° D18AC00031, for Drs. Lloyd-Smith and Gamble), National Science Foundation (Lloyd-Smith) and the Strategic Environmental Research and Development Program of the Department of Defense (SERDP, RC-2635, to Dr. Lloyd-Smith).

Disclosure forms provided by the authors are available with the full text of this letter on NEJM.org.

The findings and conclusions of this letter are the responsibility of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention (CDC). The names of specific suppliers, manufacturers or products are included for public health and information purposes; inclusion does not imply endorsement of suppliers, manufacturers or products by the CDC or the Department of Health and Human Services.

This letter was published on March 17, 2020, on NEJM.org.

Dr. van Doremalen, Bushmaker and Morris also contributed to this letter.

  1. 1 Coronavirus disease status reports (COVID-2019). Geneva: World Health Organization, 2020 (https://www.who.int/emergencies/diseases/novel-coronavirus-2019/situation-reports/)

  2. 2) Wu A, Peng Y, Huang Bet al. Genome composition and divergence of the new coronavirus (2019-nCoV) originating in China. Cell host microbe 2020; 27:325328.

  3. 3) Bai Y, Yao L, Wei Tet al. Presumed asymptomatic carrier transmission of COVID-19. JAMA 2020 February 21 (Epub before printing).

  4. 4) Zou L, Ruan F, Huang Met al. SARS-CoV-2 viral load in upper respiratory samples from infected patients. N Engl J Med 2020; 382:XXXXXX.

  5. 5) Chen YC, Huang LM, Chan CCet al. SARS in the hospital’s emergency room. Emerg Infect Dis 2004; 10:782788.

Paula Fonseca