Coronavirus can spread on surfaces, scientists say, but people remain biggest infection risk

Jennifer Rigby
·4-min read
New Zealand has seen no local coronavirus cases for more than 100 days, and has suggested that freight could be the source of a new outbreak - Getty Images
New Zealand has seen no local coronavirus cases for more than 100 days, and has suggested that freight could be the source of a new outbreak - Getty Images
Coronavirus Article Bar with counter
Coronavirus Article Bar with counter

Scientists have said that getting coronavirus from another person remains by far the most likely route of infection, despite claims that new outbreaks in New Zealand and China are linked to surfaces. 

In New Zealand, the authorities are investigating whether the country's first local cases in 102 days come from imported freight, as one of the four infected family members works in a cool store in Auckland. 

In China, officials have again pointed to frozen fish as a potential source of transmission after the virus was found on seafood packaging in the city of Yantai. The product had come from the port city of Dalian, which has seen a recent surge of cases. Another city found the virus on imported shrimp from Ecuador, state media said on Wednesday.  In June, China also said a new outbreak in Beijing was linked to traces found on a chopping board used by an imported salmon vendor. 

However, the World Health Organization website states there are currently no confirmed cases of coronavirus transmitted through food or food packaging. However, it does note that studies have shown that the virus can survive for up to 72 hours on plastic, and surface or fomite (contaminated surface) transmission is 'likely'.

Professor Jonathan Ball, a virologist at the University of Nottingham, said: "The most likely explanation in truth is always that it has come in from an infected person, because firstly the virus can't survive for long periods of time on surfaces and also because you need a reasonable level of contamination for there to be an efficient survival and transfer of the virus for somebody handling it, and for them to get infected." 

A study in the Lancet in April found that while infectious coronavirus could be detected days on some surfaces – particularly on smooth surfaces like plastic and stainless steel – several days after being introduced, it remained unclear whether a person could actually be infected by touching that surface. 

Coronavirus New Zealand Spotlight Chart - Cases default
Coronavirus New Zealand Spotlight Chart - Cases default

"The salmon in China – few of us really believe that," said Professor Ball. "But in theory, there is nothing to stop somebody heavily contaminating a surface and for that surface to potentially spread the virus if it travels. So you can never rule it out." 

He said sequencing the virus to find out what strain it was could be helpful in tracing transmission, as it could give an indication of where in the world that strain of the virus came from. 

However, he said it was true that cold temperatures – as in the refrigerated freight in New Zealand and frozen fish in China – might help the virus survive. 

New Zealand's Director General of Health Ashley Bloomfield also suggested that the cold may have played a part in the freight transmission, if it is proven. 

"We know the virus can survive within refrigerated environments for quite some time," he said during a televised media conference on Wednesday.

Coronavirus China Spotlight Chart - Cases default
Coronavirus China Spotlight Chart - Cases default

Cold temperatures have also been blamed for outbreaks at meat processing plants around the world earlier this year, including in the UK and Germany, alongside other factors that made the factories perfect incubators for the virus, including close working conditions.

Calum Semple, professor of child health and outbreak medicine at the University of Liverpool, said at the time: "If I wanted to preserve a virus, I would put it in a cold, dark environment or a cool environment that doesn't have any ultraviolet light – essentially a fridge." 

He added: "The perfect place to keep a virus alive for a long time is a cold place without sunlight." 

The same Lancet study, from the University of Hong Kong in April, found that the virus could remain stable for long periods at 4 degrees C.

Professor Ball said that if the cases are confirmed to be linked to surface transmission, it could lead to greater checks of disinfection measures at ports to help stop the spread. However he cautioned that it would still be about relative risk as to whether that was worth doing, considering that person-to-person transmission was still the leading cause of infection.  

"If this is a one-in-a-billion chance episode, it is probably not worth worrying about too much," he said. 

"It is the same with all of these things – everything is possible but it is about how possible it is. And then we have to adopt behaviours to take into account that relative risk." 

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