Dozens of food processing plants across the UK are dealing with coronavirus outbreaks among their staff.
The Food Standards Agency (FSA) said there are around 40 food factories with active outbreaks in England, Wales and Northern Ireland, with many in meat plants.
Banham Poultry in Attleborough, Norfolk, has one of the most recent outbreaks, with 75 workers testing positive for COVID-19.
Bakery chain Greggs also had an outbreak in its Leeds distribution depot, with “fewer than 20” staff testing positive on Friday, a spokeswoman said.
The 2 Sisters factory in Couper Angus, Scotland, has had 157 staff test positive and 20 of their close contacts as of Friday.
Lawrence Young, professor of molecular oncology at the University of Warwick, said factories pose a complex mix of issues that can result in higher transmission.
The virologist said the virus remains on surfaces longer in the cold, it can be difficult to socially distance in factories and many of the workers may live together or not be keen to report symptoms as they need the work.
He told Sky News: “This virus survives longer in colder environments – both in the air and on surfaces, so there is an increased risk of transmission.
“These types of viruses have a fatty membrane that is very efficiently destroyed by soap but it stabilises at about 4C.”
When it gets to zero C, it is destroyed.
“This is the case for many respiratory diseases, influenza, the common cold.”
Prof Young said food processing plants have implemented even more stringent health and safety measures than usual since the pandemic started, but there are so many details that can be missed.
“You’ve got crowded areas and busy production lines – it’s difficult for people to socially distance,” he said.
“Busy machinery can mean workers shouting across production lines which can increase aerosols and virus-containing droplets which will hang around more in cold temperatures.
“What are you doing about tea breaks, lunch breaks, toilets? The virus is so infectious you can’t let your guard down anywhere.”
How workers are getting to and from work, whether they are living in communal housing together and whether they are being careful at home is essential to look at, he added.
He said the fact many workers are paid the minimum wage and by the hour may also be a factor.
“They may not want to report symptoms because they will lose money,” Prof Young added.
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He recommended signs all over factories reminding workers to be vigilant at work and at home, lots of handwashing stations and face coverings to “instil a certain psychology about protecting others”.
The FSA said not all of the outbreaks have been at meat plants and stressed that less than 0.25% of the more than 20,000 food processing plants have been affected.
It added that it is “very unlikely” someone can catch coronavirus from food or food packaging, with the most likely cause of the factory outbreaks human-to-human contact.
It said the use of personal protective equipment should continue to be used to protect workers and prevent food contamination, in line with current health and safety policies.