A Covid-19 outbreak at a turkey processing plant may have links to car sharing, the company affected has said.
Public health officials were brought in on Monday to test about 100 staff at the Bernard Matthews site in Holton, near Halesworth, Suffolk.
The firm, which employs about 1,000 people at the site, has revealed 25 people tested positive for coronavirus.
It said there were cases from a limited number of homes in Lowestoft and Great Yarmouth from which people shared cars.
In correspondence with the Unite union, Andrew Sherwood, Bernard Matthews' human resources director, wrote: "At present, there are 25 positives and 54 are self-isolating.
"Many of those self-isolating have now been tested at home and are negative, but must remain self-isolating for 14 day as per Government guidelines."
He said there was no clear link between any of the cases "at site and the cases appear to have come from a limited number of addresses in Lowestoft/Great Yarmouth from which people car shared".
"Each case is tracked and traced looking at key information such as address, transport, work location, smoker, family/social links to other Bernard Matthews personnel," Mr Sherwood added.
"This information enables us to quickly identify colleagues that need to self-isolate."
On Monday, a joint statement from Bernard Matthews and Norfolk and Suffolk public health officials said food production and safety were unaffected at the plant.