Hundreds of workers at food processing plants in Wales have tested positive for coronavirus with outbreaks in Llangefni and Wrexham.
More than 300 cases of the virus have been identified in people working in food processing sites in Wales.
There are now 200 cases of Covid-19 associated with the 2 Sisters chicken processing plant in Llangefni, Anglesey, including household contacts of staff, and 97 confirmed cases with the Rowan Foods factory in Wrexham.
More than 1,000 tests have now been carried out on workers at Rowan Foods on Wrexham Industrial Estate where an outbreak was confirmed this month.
An investigation is also underway at the Kepak meat processing plant in Merthyr Tydfil, which is not classed as an outbreak, where there have been 34 confirmed cases since April 25 including eight since June.
Why have there been so many outbreaks in food processing plants?
One theory is that the cold environment in these factories may be helping Covid-19 to spread.
The UK Government's chief scientific adviser Sir Patrick Vallance said the working environment in meat plants could be a factor.
"They are cold, and we know the virus prefers it in the cold, there's often difficulty in keeping people physically separated, so there is that whole problem of proximity," he said.
"So the environment itself is rather a difficult one in terms of the risk and the behaviours that need to be in place in order to reduce those risks," he added.
Wales' health minister Vaughan Gething said that many staff could also be reluctant to take sick leave if they become ill.
But at the moment these are all theories and investigations are continuing in a bid to find a definitive answer.
Can you catch coronavirus from food?
The Food Standards Agency has said it is very unlikely you can catch coronavirus from food, describing the probability as "negligible."
They say that since it is a respiratory illness it is not known to be transmitted by exposure to food or packaging.
While the risk is considered to be very low the agency does add "there are significant data gaps" and a number of their assumptions are based on "data relating to other coronaviruses."
What's being done to protect workers?
There is due to be a meeting later this week between the Welsh Government, unions and employers to discuss worker welfare issues.
Public Health Wales is working with the Food Standards Agency and the Health and Safety Executive to develop new guidance for the sector.
Until then the 2 Sisters site on Anglesey has been closed and will only re-open once effective controls have been put in place.
The Rowan Foods plant in Wrexham remains operational but a site visit will take place later this week.
Is this just a problem in Wales?
Outbreaks in food processing plants are being reported around the world, including the USA and Canada, with an outbreak in Germany affecting more than 1,300 employees.
Are communities at risk?
The Welsh Government says there are no signs the outbreaks at the two sites in north Wales have spread into the surrounding communities.
Speaking at the Welsh Government daily press conference Mr Gething said: "I want to repeat these are outbreaks centred on the plants themselves, and at present there is no wider community transmission.
"But we are, as you would expect, keeping these outbreaks under very close observation and management."
Darren Hughes, director of the Welsh NHS Confederation, said identifying the two outbreaks in north Wales provided "reassurance" that the country's track and protect system was working.
He said: "Over recent days we have seen localised outbreaks of coronavirus in Wales. This news is not unexpected and in some ways it provides reassurance that these cases have been found quickly and dealt with effectively.
"By finding these cases early, we can help to prevent transmission to the wider community. It is a testament to the track and protect system in Wales that we have been able to hopefully bring these outbreaks under control before more people were impacted."