A total of 75 workers at a poultry plant in Norfolk have now tested positive for Covid-19 as part of a new cluster at a food processing plant.
So far, 347 people tested at Banham Poultry in Attleborough.
As a result of the infection rate, which is at about 22%, Banham Poultry has voluntarily agreed to close part of their site following advice from Public Health England and Norfolk Public Health.
This means that all 350 staff who work in the factory's cutting room will be asked to isolate with their households.
Those who have tested positive will be asked to isolate for 10 days. Those who have tested negative will be asked to isolate for 14 days. The area of the factory affected will be deep cleaned.
Those who work in other areas of the plant will be able to continue working and the factory will remain open.
A spokesman for Breckland Council said: "If any employee is unsure whether they are affected they should contact Banham Poultry directly.
"This action has been taken because we believe it is the most effective way to protect the wider public from further transmission. We have carefully assessed the various levels of risk to come to this decision.
This has been an incredibly tough decision for Banham Poultry, whose management team has worked tirelessly today to make arrangements for this partial closure, balancing the protection of the public, their staff and their business.
"I'd also like to thank them for their significant endeavours in assisting us with contact tracing.
"The management team at Banham Poultry is continuing to work closely with us alongside other colleagues at Breckland Council, Public Health England and the Department of Health.
"We know the workers live mainly in the Breckland, Norwich, and Great Yarmouth districts. We will be working with partners across the county to support people to isolate.
"At this stage in our investigation, these cases of infection are in staff who work in Banham Poultry and their households.
There is no evidence of increased risk to the general public. The risk of infection from food products is very low.
"The advice to people concerned about contracting the virus is to remember the basics. Continuing to wash your hands regularly and practising social distancing is the best way to protect yourself.
"If you feel unwell, even if your symptoms are mild, you should isolate with your household and get a test."