Large numbers of staff could have been unknowingly spreading coronavirus through care homes, according to the UK's largest charitable care home provider.
Data from MHA shows 42% of its staff members who recently tested positive were not displaying symptoms.
Nearly 45% of residents who had a positive test were also asymptomatic.
MHA operates in England, Scotland and Wales and has fully tested staff and residents in 86 of its 90 homes so far.
A Department for Health and Social Care spokesperson said: "Our priority is to ensure care workers and those receiving care are protected, and the latest statistics show over 60% of care homes have had no outbreak at all.
"We've set out a comprehensive support package for residents and staff, including a £600m infection control fund, testing regardless of whether you have symptoms, and a named clinical lead to support every care home.
"We recognise more must continue to be done, and have made £3.2bn available to local authorities to address additional pressures from coronavirus."
In total, 7% of MHA staff and 13% of residents received a positive test result.
Routine testing is not yet under way.
MHA CEO Sam Monaghan told BBC Newsnight: "It is not difficult to imagine that a lot of people may not have ended up dying if we'd had earlier testing and we'd been therefore better able to manage infection control in our homes."
In May, Professor John Newton from Public Health England said it would be "premature" to introduce weekly testing of care home staff and residents.
Instead, the government promised one universal test for everyone in care homes in England by early June.
Many social care providers have complained that hasn't happened.
Mr Monaghan continued: "I think it's very difficult not to see that the only real way that this can have come into our homes is through staff picking it up, just through the community contacts they would have had.
"I think that is what is so hard for all our staff, because they care. But if they don't know they've contracted the virus, how can you manage this?
"We lobbied right from the outset that routine testing was going to be absolutely vital in terms of us managing and doing effective infection control in our homes. The government still isn't offering that.
"What does it say to the valuable people who work and live in care settings that it's 'premature' to test them weekly when Premiership footballers are being offered a test, not once, but twice a week?"
ONS figures show more than a quarter of all coronavirus deaths in England and Wales have happened in care homes.
MHA has shared with Newsnight its log of suspected and confirmed cases.
It says 398 people have died in its care homes since the crisis began. Three MHA staff have also succumbed to the virus.
So far 930 people have recovered from suspected or confirmed Covid-19.
This data also shows less than half of the residents who died ever got a test.
Heather Grange care home in Burnley lost 10 residents. Only four were tested for coronavirus.
Manager Mark Quarmby said: "Once the virus took hold of some of our residents, it was relentless. We'd see cases where people literally showed some symptoms on a Friday and by Tuesday they'd passed away.
"There was no testing. I actually had a conversation with Public Health England and asked for tests. I was categorically told there was no testing for care homes in the North West. We were on our own.
"The early warning, that testing, could have changed outcomes. People could have lived the next two, three, four, five years. It makes me very sad."
Public Health England said it "worked with Heather Grange care home and local partners to provide appropriate guidance and support to minimise the spread of Covid-19. Testing was arranged in line with policy at that time".