Outbreaks of coronavirus have been reported at meat factories around the world, including at multiple sites in the UK.
In October, 75 workers tested positive at a turkey plant in Norfolk, while 72 cases were confirmed at a food processing facility in Suffolk.
Weeks before, more than 170 infections were recorded at a meat plant in Cornwall.
Elsewhere in Europe over summer, lockdown measures were tightened in a German county that had seen a large increase in Covid-19 cases linked to a slaughterhouse, where more than 1,500 workers contracted coronavirus.
And meat factories in the US have also shut over Covid-19 and seen hundreds of workers fall ill with the virus.
Staff working in close proximity to each other, poor employment contracts and cold temperatures are some of the theories behind the outbreaks, but industry representatives in the UK insist the reason for them is a “mystery”.
“There is no proof in science that a meat factory is any different to a chilled food factory doing other work,” David Lindars from the British Meat Processors Association (BMPA) told The Independent.
“Nothing has been said about our working environment in particular that causes any of these outbreaks that we know of from a science point of view. It is a mystery as to why.”
Mr Lindars, the trade body’s technical operations director, added: “You must not forget we never stopped as an industry. The car industry stopped and lots of other industries stopped.
“We have kept going and, to date, we have been pretty good at feeding the nation and ensuring red meat is on the shelves to retailers without mass closures that has happened in other countries.”
But the Unite union says it has repeatedly warned that outbreaks at meat factories in the UK were likely.
Experts believe the unique conditions at meat factories could be partly behind the outbreaks.
Professor Rowland Kao, a professor of veterinary epidemiology and data science at the University of Edinburgh, said that “low temperatures have also been shown to result in higher rates of transmission of influenza in experimental studies, and to improve the survival of other coronaviruses such as MERS-CoV. While this is not proven for Covid-19, similar mechanisms may apply.”
And Lawrence Young, a professor of molecular oncology at the University of Warwick, agreed that the environment inside factories and slaughterhouses would be perfect for coronavirus to linger and spread.
“The virus survives on cold surfaces and, in the absence of ventilation and sunlight, virus-containing droplets from infected individuals are more likely to spread, settle and stay viable,” he said.
“Meat factories and slaughterhouses are locations where people are engaged in higher levels of physical activity, and where maintaining physical distancing in internal spaces will be difficult, and difficult to monitor,” added Prof Kao. “Both these factors may increase the likelihood of transmission.”
Professor James Wood, an infectious disease epidemiologist at the University of Cambridge, told The Independent it also might be difficult to social distance “on a fast moving slaughter line”, and the “substantial air movement that exists in or across many slaughterhouses and meat plants” could be another possible explanation.
“That having been said, many meat plants do have established practices that involve standard use of PPE [personal protective equipment] which they should find relatively easy to extend,” Prof Wood added.
“As soon as the button was pressed at the end of March, our industry spent quite a few million pounds putting in Perspex screens, extra PPE etc,” Mr Lindars from the BMPA told The Independent. “We were very fast to react to government advice.”
He said some factories have “reduced their capacity and efficiency” by spacing sheep carcasses out more on the slaughter line to make it easier to social distance.
But Bev Clarkson, national officer at Unite, said that close working conditions were “no excuse” for the outbreaks.
“While it is true that there are difficulties in maintaining staff distancing at many sites, this is no excuse – especially since similar outbreaks in the US and other countries have been widely reported on,” Ms Clarkson said.
She said “low wages” and “poor employment contracts” could also play a role in outbreaks at meat-processing factories.
“Many employers are refusing to provide any financial support for those presenting with symptoms, so it is inevitable that some staff will simply hope they don’t have it and go into work,” Ms Clarkson said. “Employers have a duty to treat their staff better and stop the spread of the disease.”
Workers can get statutory sick pay of £95 a week if they are ill or have to self-isolate because of coronavirus.
When outbreak centred on the Kober meat-processing plant in West Yorkshire was confirmed by owner Asda in June, the company said colleagues needing to self-isolate would “receive full pay”.
Additional reporting by agencies