A local lockdown could be enforced to get the coronavirus outbreak at a food factory under control, Public Health Wales has said.
Giri Shankar said “aggressive control measures” were being used on Anglesey to stop the infection.
So far 158 workers at 2 Sisters in Llangefni have tested positive for Covid-19.
All staff are self-isolating and the factory has closed as workers continue to be tested.
Dr Shankar told BBC Radio Wales local lockdowns could be something “we need to consider”.
“At the moment the outbreak is localised to members of staff working in that particular factory,” he said.
“There is no evidence of widespread community transmission, but therefore I think at this point of time we need to weigh all the options carefully before going into a blanket lockdown.
“It is a possibility, providing there is enough evidence to support such an action.
“We need to see how the outbreak progresses.”
An outbreak team was established last week.
“That has been meeting daily and advocating aggressive control measures so that we can halt the spread of the infection,” Dr Shankar said.
“At the moment all the employees at that particular factory have been offered testing.”
“Of the remaining tests that are still out in the lab we still expect to see a further increase but all the control measures are in place, the staff are self-isolating and the factory is temporarily closed,” Dr Shankar said.
He was confident the outbreak could be contained if people followed self-isolation advice.
“As we begin to ease lockdown in society, such clusters of outbreaks will occur and we do expect these,” he said.
“And these will uncover a pocket of asymptomatic infection that existed.
“So we shouldn’t be surprised, but we should be concerned and take swift action.”
Economy Minister Ken Skates has said it is essential to keep the Anglesey outbreak “as local as possible”.
On Sunday he did not rule out restrictions remaining in place on Anglesey.
He said: “That will help contain the virus, and that, in turn, help Anglesey open up its economy sooner, and that is something I think the island will welcome and I think the entire population of Wales will welcome.”
2 Sisters has said “the health, safety and well-being of our colleagues is ultimately the thing that matters most”.
It said it would not tolerate unnecessary risks to its workforce at the plant.