Seventeen new cases of coronavirus have been identified amongst employees of a poultry processing plant on Anglesey.
It brings the total number of confirmed cases at the 2 Sisters Food Group in Llangefni to 175, with the Welsh Government unable to rule out the possibility of enforcing a strict local lockdown.
Over 400 members of staff have been tested since Thursday.
The First Minister Mark Drakeford said on Monday that any decision on further lockdown measures would not be "taken lightly", but stressed that the approach would be "proportionate and draw on the evidence."
Public Health Wales said the latest increase is the result of a "focused" track and trace programme, and "does not mean that the spread of infection is increasing."
Employees and contractors from the factory have been asked to self-isolate for 14 days to help limit the further spread of the virus, following confirmation of multiple cases in the workforce.
Dr Christopher Johnson, Consultant in Health Protection at Public Health Wales, said what's happened on Anglesey is a reminder that coronavirus is still circulating, sometimes invisibly.
Dr Johnson 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.
“We all have a part to play in preventing the spread of coronavirus by sticking to social distancing guidelines – that’s staying two metres away from others – and washing hands regularly.
“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."