Norfolk's director of public health has said it is "very difficult" to say whether supermarkets are serving as hot spots for the spread of coronavirus.
Supermarkets have stayed open throughout the Covid-19 pandemic, as the government defines them as "essential" retailers.
Bosses are responsible for making them Covid-safe, with Tesco, Asda, Sainsbury's, Morrisons, Aldi and Waitrose among those saying they will deny access to people not wearing masks, unless they have a valid medical reason.
But, at a meeting of Norfolk County Council's scrutiny meeting, Conservative county councillor John Timewell said he was concerned measures were not as rigorous as they could be and questioned the role of supermarkets in spreading Covid-19.
Dr Louise Smith, Norfolk's director of public health, said: "In terms of the role of supermarkets in transmission, that is a very difficult question to answer.
"We do see significantly high numbers of reports of people who have been to supermarkets as part of contract tracing, but that reflects how supermarkets are one of the places that everybody does go.
"It is hard for us to unpick whether that's 'noise' in the system or whether they have been infected in a supermarket.
"It's something that, nationally and locally, we need more analysis of."
She said it was the responsibility of supermarket bosses to ensure their stores were Covid-safe.
But she said she would feed Mr Timewell's concerns back to district council environment health teams, which had responsibility for enforcement.
It comes as a convenience store worker, who received complaints for asking customers to wear masks, hit out at the "disrespectful" people who "refuse to follow the law".
Joanna Wright, who works at the East of England Co-Op's food store on Beresford Road in Great Yarmouth, claimed "around a third" of customers refuse to wear face coverings, with many becoming defensive and aggressive when challenged.
Coronavirus case numbers in Norfolk have fallen after a rise over Christmas and early January.
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