Public health authorities have confirmed that 18 people have tested positive for coronavirus at a Bernard Matthews factory in Suffolk.
The company said over 100 tests have now been carried out at the plant in Holton, near Halesworth, with the majority returning negative results.
Testing will continue this week, and those who have tested positive have been instructed to self-isolate along with their contacts.
Most of the 18 live in Great Yarmouth and Lowestoft, according to a joint statement from Norfolk and Suffolk's public health teams.
David Edwards, health protection consultant for Public Health England East of England, said: "We are working closely with the organisation, local authority and NHS partners to provide public health advice and help stop the spread of the virus.
"Close workplace contacts have been identified and given self-isolation advice."
ITV Anglia spoke to Stuart Keeble, Suffolk's director of public health
It is the second outbreak at a poultry factory in the Anglia region, after over 100 staff tested positive at Banham Poultry in Attleborough at the end of August.
Bernard Matthews said they think the staff who tested positive caught the virus "in the community", and that they would continue to enforce their Covid-19 safety measures.
Suffolk County Council have praised the "speed and thoroughness" of the turkey producer's management in handling the outbreak.
The county's director of public heath, Stuart Keeble, added: "I’d like to reassure people that this is, at this stage, a relatively small number of cases and that the situation is being very carefully managed by all the partners working closely together."
Food production sites have been vulnerable to outbreaks during the Covid-19 pandemic; in August the Greencore factory in Northampton, which makes sandwiches and Sushi for Marks and Spencer, was forced to suspend production after over 300 staff caught the virus.
Norfolk County Council have offered their counterparts in Suffolk help via their locally-run contact tracing service.