Coronavirus testing has uncovered 170 positive cases of Covid-19 at a major pork processing site in Cornwall.
Five hundred workers at Pilgrim's Pride in Pool, near Camborne, have been tested as part of an NHS contact tracing exercise.
Most of the staff who tested positive for the virus did not exhibit any symptoms.
Pilgrim's Pride, a multinational processor which employs more than 50,000 people and operates in the US, UK and Europe, said that 'from the outset' the firm had 'worked conscientiously to do all we can to protect our workforce and the local community'.
Cornwall Council confirmed those staff members with Covid-19 were now isolating in line with government regulations.
"In total, almost 500 employees at the factory have been tested and the vast majority of the cases who tested positive were not displaying symptoms," the council said.
Rachel Wigglesworth, interim director for Public Health for Cornwall Council, added: "In finding people who weren't displaying symptoms we have potentially stopped much wider spread in our communities".
It comes as 18 factory workers at a Bernard Matthews turkey processing site in Suffolk tested positive for the coronavirus earlier this week.
Public health officials tested 100 members of staff who work at the plant, located in Holton, near Halesworth.
Bernard Matthews said those who tested positive for Covid-19 - from the Great Yarmouth and Lowestoft areas - were now self-isolating.
The turkey processor employs around 1,000 people at the Suffolk site.