A number of cases of COVID-19 transmission suggest that contaminated surfaces may play a role in spreading the disease.

This week, Reuters reported that the virus was detected on meat products in eastern China imported from New Zealand, Argentina, and Brazil.

A lift button at the Rydges Hotel, a bus in Auckland, and a bin in a Christchurch managed isolation facility have also been identified as possible sources of coronavirus infections.

The SMC asked experts to comment on the spread of coronavirus via surfaces.

Professor Nigel French, Professor of Food Safety and Veterinary Public Health, Massey University, comments:

What have we learned about the survival of the virus on surfaces?

“A small number of published studies have addressed this question. One study examined survival of infectious virus on different surfaces at 22°C and a relative humidity of approximately 65%.The data showed that infectious virus was detected on nonporous surfaces for 2 to 4days, compared with detection on porous surfaces for only 30min to 2days. More specifically, the virus remained infectious for at least 30 minutes on paper, 1 day on wood and cloth, 2 days on glass and banknotes and for at least 4 days on stainless steel or plastic. These findings are supported by another article that also showed SARS-CoV-2 was more stable on plastic and stainless steel than on cardboard and copper (which is known to have antimicrobial properties).

“Evidence from a recent study of the stability of SARS-CoV-2 in simulated saliva showed survival decreased with increasing humidity and temperature. However, the authors only examined ranges from 20 to 80% relative humidity and 24 to 35°C temperature. There is a need for experimental studies that examine survival on surfaces over a wider range of environmental conditions, including freezing temperatures.”

What practices are in place to minimise the risk of spread via surfaces in food production?

“Standard food hygiene practices already in place in the food industry minimise the risk of contamination of surfaces and food from potentially infected workers. In New Zealand, these were further enhanced during the early stage of the pandemic, following advice from the New Zealand Food Safety Science and Research Centre and strict protocols and guidance developed with the Ministry for Primary Industries (MPI). These include on-site health checks, use of appropriate PPE, enhanced physical barriers and distancing, hand hygiene, cleaning and disinfection of high-contact surfaces, and ensuring any workers showing signs of infection stay at home.”

How could the spread of the virus be tracked and traced along the food supply chain?

“The presence of virus can be detected using standard molecular tests applied to swabs taken from surfaces, including food packaging. However detection alone does not indicate that the virus remains infectious, the source of contamination or the risk of transmission to people, which is generally considered to be extremely low from contaminated surfaces. The World Health Organization advises that transmission by airborne droplets and aerosols is the dominant pathway for COVID-19 infection.”

Conflict of interest statement: “I’m Chief Scientist for the New Zealand Food Safety Science and Research Centre.”

Dr John Taylor, Senior Lecturer in Virology, School of Biological Sciences, University of Auckland, comments:

What have we learned about the survival of the virus on surfaces?

“Several studies have addressed this issue under laboratory conditions. This usually involves spotting a small droplet containing infectious virus on a sterile surface, leaving it to dry and later washing off the virus into sterile liquid and then measuring the infectivity in cells grown in a laboratory. Most studies indicate that virus can remain infectious for between 2 – 4 days although on some hard surfaces like plastic, stainless steel or glass this can be extended to anywhere from 4-7 days.

“It’s possible that these lab studies overestimate the duration that the virus can remain infectious in the environment when it gets onto surfaces via respiratory droplets – where the virus is contact with antimicrobial chemicals found in saliva, sweat or other bodily secretions. Outside of laboratories, viral RNA, the genetic material that is detected by the standard clinical test, can be found in a high proportion of surfaces in hospitals and quarantine facilities housing symptomatic or asymptomatic patients. But very few of these studies test for infectious virus, suggesting that although the virus leaves behind a chemical calling card in its RNA, it loses infectivity rapidly.”

How does the risk of transmission via surfaces compare to other modes?

“It’s difficult to know this exactly because most people contracting infections are exposed to both direct and indirect sources of the virus. There is a real risk of transmission via contaminated sources but direct person-to-person transmission via respiratory droplets is likely to be more important.”

What are the best ways to minimise the risk of spread via surfaces?

“This virus is very sensitive to chemical inactivation by detergents and other common sterilants and also to heat, so rigorous cleaning of quarantine facilities is probably the most important thing we can do while we’re free of community transmission.”

No conflict of interest.

Geoff Willmott, Associate Professor of Physics and Chemistry, University of Auckland and Deputy Director for Commercialisation and Industry Engagement at the MacDiarmid Institute for Advanced Materials and Nanotechnology, comments:

What have we learned about the survival of the virus on surfaces?

“The viability of SARS-Co-V2 on surfaces has been studied by a relatively small collection of labs which are able to work with the live virus. Typically, the virus persists for a couple of days on common surfaces like stainless steel and plastics, including PPE materials. In extreme cases, the virus has remained viable for 3-4 weeks, but in a recent Australian study this was only observed when using high viral loads (equivalent to the most infectious patients) with samples kept in the dark – the virus is rapidly inactivated by UV radiation in sunlight. These results are broadly consistent with studies of influenza and the coronaviruses SARS and MERS prior to the pandemic.”

Does the surface material matter?

“By April, a US study had established that copper surfaces produced much lower Covid-19 viability than stainless steel or plastic. This isn’t a surprise – copper has known antimicrobial and antiviral properties, which is one reason why it is favoured for touch points like taps. Due to the pandemic, technologies are emerging such as new copper-based alloys with proven antiviral performance, and a method to cold-spray copper on to stainless steel surfaces. Surfaces which absorb droplets (cardboard, cotton) also seem to reduce viability.”

What are the best ways to minimise the risk of spread via surfaces?

“Directly studying the viability under controlled conditions is only one part of a broader and much more complex problem. Viability falls with rising humidity and temperature, and will depend on the size and composition of a droplet which lands on the surface. This in turn depends on generation and size distributions of droplets, how droplets travel to and land on the surface, how they evaporate, and environmental factors.

“Each of these topics can be studied in isolation (and this is happening), but in the ‘real world’ they are all linked together. As a result, at the moment it is not always clear whether (or in which circumstances) surface transmission is more significant than direct or airborne transmission. That’s a problem worthy of further study, but should not distract from the well-known practical first steps which are known to combat all transmission paths, such as regular hand-washing and wearing masks in public.”