Living samples of the coronavirus have been detected on frozen food packaging in the east China port city of Qingdao, according to the Chinese Centre for Disease Control and Prevention (CDC).
The announcement came after a CDC investigation into an outbreak of Covid-19 in Qingdao, which started last month and was linked to two port workers who had been patients at the same hospital.
However, the agency has not shown conclusively whether the workers were infected by handling infected packages or contaminated the packages themselves after contracting the virus somewhere else.
The CDC said its researchers detected the live samples on a package of frozen cod that had been handled by the two workers.
“It is the first time in the world that living novel coronavirus has been isolated from the outer packaging of cold-chain food,” the CDC said in a statement published late on Saturday.
It did not identify the source of the cod but warned that people handling frozen objects could be at risk as the packaging showed the coronavirus could be “imported from a long distance”.
In earlier tests conducted across China on frozen food packaging and freight, just 22 out of 2.9 million samples tested positive for Covid-19. And in those instances, the viral load was low and no living samples were found, the CDC said.
Despite the new findings, Professor Ben Cowling, head of the epidemiology and biostatistics division at the University of Hong Kong’s School of Public Health, said the study did not prove that people could be infected through contaminated packaging.
“We already knew it was a theoretical possibility that infection could spread through contaminated objects, and this study does not change that,” he said.
“I still think it is an uncommon route of transmission. Whenever we can find virus RNA we assume there is a risk there was live virus there at some point,” he said, referring to the molecule that carries genetic codes in viruses.
“If it’s dead now, it must have been alive at some point, and we know viruses can survive freezing,” he said.
The two Qingdao dock workers tested positive for Covid-19 on September 24 despite not showing any symptoms. In the following days, a further 13 infections were confirmed in the city, most of which were linked to the same hospital the men had stayed in and, specifically, its CAT scan room, state media reported on Friday.
A five-day testing programme covering nearly 11 million Qingdao residents – including 20,000 workers at the port – was completed last week.
The Qingdao cluster ended China’s run of 55 days without any local transmission of the coronavirus, which has now infected almost 40 million people around the world.
In its latest statement, the CDC reiterated comments made earlier by the World Health Organization that there was no evidence to show the coronavirus could be transmitted by eating frozen food.