They'll now self-isolate for seven days and their contacts will be traced by the NHS.
Kirklees Council have confirmed that 165 people who work at the Kober meat factory in Cleckheaton have now tested positive for coronavirus, following a local outbreak of the virus at the site.
They say the testing is likely to have identified people who had mild illness, or even some not showing symptoms who may have otherwise gone undetected and could have infected others.
These positive cases are now being followed up by the NHS Test and Trace programme and they are being advised to self-isolate for 7 days. Anyone identified as a close contact of a positive case is being advised to self-isolate for 14 days.
The authority say the detection of localised outbreaks of Covid-19 are now likely to become more common across the country, following the introduction of the NHS Test and Trace scheme.
The Kober site at Cleckheaton is owned by Leeds-based Asda, and supplies the supermarket chain with some of it's meat and bacon products.
Rachel Spencer-Henshall, Director of Public Health at Kirklees Council, said:
“I’d like to thank KOBER for acting quickly and working with us and Public Health England to help manage this outbreak.
“They reopened their factory on 23 June on a reduced capacity and only colleagues that have been tested and declared fit to return are on site.
“We’re satisfied with health and safety measures on site which include separation of colleagues on different shifts and as an additional precaution, checking the temperature of colleagues before they enter the site.
“Our advice to residents is to continue to socially distance, wash hands regularly for 20 seconds with soap and water and get tested if they have symptoms.
“Providing you have not been contacted and told otherwise, you can continue to leave the house following the latest government advice.”