There are now 200 confirmed Covid-19 cases linked to the coronavirus outbreak at a Welsh meat factory.
Public Health Wales (PHW) has confirmed 25 more cases at the 2 Sisters chicken processing plant, which employs about 500 people in Llangefni on Anglesey.
Three Welsh meat and food plants now have Covid-19 among its workers - 34 cases linked to Kepak in Merthyr Tydfil and 70 at Rowan Foods in Wrexham.
Wales' health minister said government will see if the sector should improve.
PHW have carried out more than 450 Covid-19 tests as a result of the Anglesey outbreak, which is the reason why schools will not open in the county on Monday.
The chicken processing plant in Llangefni, the smallest of food giant 2 Sisters' 12 plants across the UK, has temporarily closed as a result of the outbreak.
"Incidents like this are a reminder that coronavirus is still circulating, sometimes invisibly, and that we all need to be vigilant," said Dr Graham Brown of PHW.
Birmingham-based 2 Sisters is one of the UK's biggest food manufacturing companies, employing about 18,000 people across the country and with an estimated £3bn annual turnover.
2 Sisters supply major outlets like Marks & Spencer, KFC, Asda and Aldi - although the company say none of their major customers are supplied from the Anglesey plant.
'No evidence of wider community transmission'
Health Minister Vaughan Gething said there was no evidence of wider community transmission following the outbreaks at 2 Sisters and Rowan Foods - and did not see a need for local lockdowns in response.
Mr Gething said outbreaks in meat and food processing plants had been a feature of the pandemic around the world and food producers had been "generally good" at complying with Covid-19 workplace regulations.
However, he said: "We also know in the meat processing sector, operating margins can be very tight, many people are employed on fairly low pay and levels of statutory sick pay mean many people feel they have no choice but to carry on working when they are ill."
The minister said the government would look at the sector "within a very quick period of time" to understand if officials needed to do more.
Cases of coronavirus have generally fallen across Wales, Mr Gething said, with fewer than 100 cases each day in the first few weeks of June.
But he revealed on Tuesday that there had been 34 cases associated with Kepak in Merthyr Tydfil since April, with eight new cases since the start of June - on top of the 200 cases at 2 Sisters and 70 at the Rowan Foods outbreak in Wrexham.
A union official has written to Rowan Foods to express "extremely worrying and developing issues" at the plant, which the company has denied.
In a letter seen by BBC Wales, Unite regional officer David Griffiths says one of the workers who tested positive for Covid-19 returned to work after isolating for six days.
People who have tested positive must self-isolate for at least seven days from when their symptoms began.
He writes: "The reason for my letter/email is to raise specific and extremely worrying and developing issues at the Wrexham site.
"We have had many members contacting us in relation to the ongoing situation of colleagues being tested as Covid-19 positive that were in work immediately before their positive tests."
He added he had been told a manager "returned within six days of a positive Covid-19 test".
"This being a food manufacturer I am astonished at this happening," he wrote.
He said after two managers tested positive "no care or consideration" was made to workers who came into contact with those infected.
A statement from the Oscar Mayer Group, which runs Rowan Foods, said it had worked hard since March to implement measures to protect staff.
"We have reviewed potential risks of Covid-19 and have proactively made significant operational changes at the site to maintain social distancing, including various mitigations such as screens and visors," it said.
"In addition, we have implemented a behavioural safety system and social distancing champions throughout the factory to ensure colleagues are socially distancing."
What is happening at Kepak?
Jason Stevens, Usdaw union area organiser, said the priority at Kepak was to "put in place necessary safety measures and ensure that they are adhered to".
He added: "Risk assessments continue and along with our Usdaw reps on site we are holding regular meetings with the company seeking to improve safety on site."
Coronavirus regulations in Wales state workplaces must take "all reasonable measures to ensure that a distance of two metres is maintained between person on the premises and waiting to enter the premises".
A fresh lockdown has been ordered in the German state of North Rhine-Westphalia after a coronavirus outbreak linked to a meatpacking plant there.
The Food Standards Agency said it was "very unlikely you can catch coronavirus from food" as the virus is a respiratory illness.
Dr Brown, consultant in communicable disease control for PHW, said at Rowan Foods the "testing process is ongoing" and additional cases have been found.
"This does not mean that the company has been identified as the source of the infection, or that finding additional cases means the infection is increasing," he added.
"However, we are identifying previously asymptomatic individuals that work for Rowan Foods Ltd with the infection."