March 18, 2020

expert reaction to correspondence looking at air and surface stability of SARS-CoV-2

A correspondence piece, published in The New England Journal of Medicine, reports on the air and surface stability of SARS-CoV-2.

Prof William Keevil, Professor of Environmental Healthcare, University of Southampton, said:

“This new work [1] is not surprising because we showed in the flagship journal of the American Society for Microbiology, mBio, long term survival of the similar human coronavirus 229E (HuCoV-229E) on plastics, ceramics, stainless steel and glass for 4-5 days. The virus was inactivated on copper in just minutes and its RNA destroyed [2].  Duan et al. [3] also showed SARS-CoV-1 survived 5 days on wood, paper, plastic and glass surfaces. Implications are that in a closed environment a potentially infectious aerosol of small particle size can remain suspended in air for some time before landing on surfaces – hence being outdoors or opening windows is probably a good thing. However, this all depends on droplet size – aerosols are typically very small in size while coughs produce typically larger particles which settle quickly, although there is a distribution of size range with some small particles being produced which are small enough to remain suspended for longer. This needs further research with COVID-19 patients to ascertain the extent of small particle production in their coughs. Survival of coronaviruses for days on touch surfaces (not the 2 hours regularly cited by some government advisers) is a hygiene risk, and it is difficult to avoid touching fomites such as door handles and push plates, bed and stair rails, public touch screens etc. It re-emphasises the need for good personal hygiene such as washing hands rigorously throughout the day, or using an alcohol hand gel, and avoid touching the eyes, nose and mouth. The latter being extremely difficult because humans are tactile people and touch their faces many times an hour.

“So why are the new data from the Doremalen et al. report showing survival on copper for 4 hours different from ours taking just minutes?  Clearly, they are using a different virus and culturing in Vero-E6 kidney cells while we culture HuCoV-229E in MRC-5 lung cells.  Our human cells were maintained in culture medium with 1mM GlutaMax-1; their cells appear to have been maintained in culture medium with 1 mM L-glutamine.  GlutaMAX-1 (L-alanyl-L-glutamine) is a dipeptide substitute for L-glutamine and can be used as a direct substitute for L-glutamine at equimolar concentrations in both adherent and suspension mammalian cell cultures with minimal or no adaptation. It is highly soluble, heat-stable, and improves growth efficiency and performance of mammalian cell culture systems. A benefit of using GlutaMAX-1 is that it eliminates problems associated with the spontaneous breakdown of L-glutamine into ammonia during incubation, allowing for longer lasting cultures.  Importantly, glutamine binds copper and its spontaneous break down at physiological pH to ammonia which reacts with copper to precipitate Cu(OH)2. This would give a partial passivation effect, making the copper surfaces less antiviral while our GlutaMAX™-1-fed viral cultures would not; hence explaining their longer time for copper inactivation.

“This is one of the reasons we decided GlutaMAX-1 was the better option to avoid potential copper binding problems when culturing coronavirus or other viruses prior to surface contact experiments.

“Nevertheless, our paper and the new one show copper alloy surfaces are better than other surfaces for inactivating coronavirus and preventing its spread via fomite contact. Our many laboratory studies describing the antibacterial, antiviral and antifungal properties of copper alloys have now been successfully translated into healthcare settings where worldwide studies have shown a 90% reduction in bioburden on touch surfaces in hospitals and a 58% reduction in infection rates in intensive care units [4]. This old fashioned material needs serious reconsideration for incorporation into our everyday environment.

1. Doremalen N, Bushmaker T, Morris D, et al.  Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. N Engl J Med.  DOI: 10.1056/NEJMc2004973

2. Warnes S, Little Z, Keevil C. (2015). Human coronavirus 229E remains infectious on common touch surface materials.  mBio 2015;6:e01697-15.       

3. Duan S, Zhao X, Wen R, et al. Stability of SARS coronavirus in human specimens and environment and its sensitivity to heating and UV irradiation. Biomed Environ Sci 2003;16:246-55.

4. Michels H, Keevil C, Salgado C, et al. From laboratory research to a clinical trial: copper alloy surfaces kill bacteria and reduce hospital-acquired infections. Health Environ Res Design J 2015;9:64-79.

Prof Paul Hunter, Professor in Medicine, University of East Anglia (UEA), said:

“The paper by van Doremalen and colleagues in the New England Journal of Medicine was focused primarily on the survival of SARS-CoV-2 and SARS-CoV-1 on a range of surfaces. Their conclusions have been broadly in line with what people have been saying for some weeks survival on surfaces tends to last at most about 72 hours (on plastic particularly), though this is not an absolute. On some surfaces the virus dies much quicker and on plastic small amounts can persist a bit longer.

“The authors also looked at survival in aerosols and the virus was able to survive in aerosols for a few hours, at least. However, this does not necessarily change our view of the risk from COVID-19. The authors used a nebulizer to generate aerosols of the virus. However, COVID-19 is primarily a droplet spread infection, so aerosols are not a particularly valid model of transmission. Droplets fall out of the air quite quickly compared to aerosols and so the risk remains from standing within about a meter or so of a case or from touching those surfaces onto which such droplets have settled. The advice remains not to get too close to possible cases and wash your hands regularly, especially after touching surfaces before touching your own face.”

‘Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1’ by Munster et al. was published in The New England Journal of Medicine.

All our previous output on this subject can be seen at this weblink: www.sciencemediacentre.org/tag/covid-19

Declared interests

None received.