Seventeen new cases of coronavirus have been identified among employees at the 2 Sisters chicken plant on the Isle of Anglesey.
Public Health Wales (PHW), which carried out a rapid screening exercise at the weekend, said the total number of cases at the plant now stands at 175.
More than 400 samples have so far been provided during the screening process.
PHW said the increase is "as anticipated" when a focused track and trace programme is implemented, and does not mean the spread of infection is increasing.
Employees and contractors from the processing plant have been asked to self-isolate for 14 days to help limit the further spread of the virus.
Dr Christopher Johnson, consultant in health protection at Public Health Wales, said: "We have recorded an increase of 17 confirmed positive cases of coronavirus, bringing the total cases in the outbreak to 175.
"Since we commenced targeted testing last Thursday, over 400 members of staff have provided samples.
"The deployment of rapid test and trace facilities has helped identify this situation, and we will continue to keep control measures in place to bring the outbreak to a rapid conclusion.
"Incidents like this are a reminder that coronavirus is still circulating, sometimes invisibly, and that we all need to be vigilant."
Dr Johnson said everyone has a part to play in preventing the spread of coronavirus by sticking to social distancing guidelines and washing hands regularly.
He added: "Employees who test positive are being contacted through the 'test, trace and protect' process and provided with additional advice for themselves, household and other contacts.
"I wish to remind everyone that if you or a member of your household develop symptoms of cough, fever or change in sense of taste or smell, you must book a test for Covid-19 you should do so promptly to help control the spread of infection."
Public Health Wales said it continues to work in partnership with the employer, Anglesey and Gwynedd Councils, the Health and Safety Executive, the Food Standards Agency, and Betsi Cadwaladr University Health Board to manage the incident.
The Food Standards Agency has advised it is very unlikely that you can catch coronavirus from food. Covid-19 is a respiratory illness and it is not known to be transmitted by exposure to food or food packaging.
