Covid-19 can survive on frozen meat and fish for up to three weeks, a study has found, as scientists warn that contaminated food may cause outbreaks.

Individual pieces of salmon, chicken and pork from supermarkets in Singapore were sliced into cubes then a sample of the virus was added to them.

The meat and fish was stored in conditions which simulate those used to transport food between countries - 4C (standard refrigeration temperature) and minus 20C (standard freezing temperature).

Scientists found that infectious Covid-19 was still present on the samples after 21 days.

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They are now warning that this may explain outbreaks in countries that have not had any coronavirus cases for long periods - and could lead to future spikes.

The study states: "An explanation is required for the re-emergence of Covid-19 outbreaks in regions with apparent local eradication. Recent outbreaks have emerged in Vietnam, New Zealand and parts of China where there had been no cases for some months.

"Importation of contaminated food and food packaging is a feasible source for such outbreaks and a source of clusters within existing outbreaks.

"While it can be confidently argued that transmission via contaminated food is not a major infection route, the potential for movement of contaminated items to a region with no Covid-19 and initiate an outbreak is an important hypothesis.

"An infected food handler has the potential to become an index case of a new outbreak. The international food market is massive and even a very unlikely event could be expected to occur from time to time."

Frequent hand washing and thorough cleaning of equipment at food processing sites is recommended by the researchers to reduce the chance of Covid-19 spreading this way.

Prof James Wood, head of the Veterinary Medicine department at the University of Cambridge, told The Sunday Telegraph: "The authors discuss, very sensibly, how it is important that factory workers must be incentivised not to go to work when symptomatic or in contact with Covid-19 cases."

The study, which is yet to be peer reviewed, was published on the bioRxiv website here.

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