A further 18 workers at a Bernard Matthews turkey plant have tested positive for coronavirus, bringing the total to 36.
Food production at the processing facility in Holton, near Halesworth in Suffolk, has not been affected by the outbreak.
The staff who tested positive are self-isolating at home, and 123 workers have so far been tested or are due to be tested.
Most have returned negative results.
As with the 18 positive cases announced on Monday, most of the 18 new positive cases announced on Wednesday concern workers who live in the Great Yarmouth and Lowestoft areas.
Stuart Keeble, Suffolk's director of public health, said: "The swift and thorough work of our local contact tracers and staff, working alongside Bernard Matthews, has quickly identified these additional cases and we've been able to advise them to self-isolation straight away."
Bernard Matthews has had controls in place since March to manage and reduce Covid-19 infections, including regular temperature checks, staff working in bubbles, Covid marshals, masks and visors and social distancing throughout the site.
A spokesperson for Bernard Matthews said: "We are grateful for the help of all local agencies and we fully support their objectives to protect the local community.
"We believe a number of cases were initiated in the community, but nevertheless we will continue to enforce our robust Covid measures as we enter into our busiest period of the year."