Coronavirus outbreaks are up to 20 times more likely to occur in large care homes, according to the biggest study of its kind in the UK.
Edinburgh University researchers examined infection patterns at nearly 200 homes and found the chance of clusters of cases tripled with every additional 20 beds.
For homes with fewer than 20 residents, the risk of an outbreak was as low as 5 per cent. But for homes with more than 60 residents it soared to between 80 and 100 per cent.
More visitors and a revolving door of care staff, often agency workers who do shifts at other homes, are thought to be the driving factor behind the increased risk.
The finding will pile more pressure on ministers to set out clear strategy for how they plan to protect care homes in the event of as second Covid-19 wave during winter.
A failure to do so during the first outbreak has seen nearly 30,000 care home residents die from the disease.
At the peak of the crisis, 25,000 hospital patients were discharged into care homes without being tested for Covid-19, allowing them to pass it to staff and frail residents.
Virus-free home: Temple Grove Staff and resident Karen Emery. Almost 30,000 more care home residents died in England and Wales during the pandemic compared to the same period in 2019, including a third who did not have the virus
In the latest study, researchers looked at infections at 189 care homes in the NHS Lothian area in Scotland where more than 400 people died from the disease in total.
The research is thought to be the broadest analysis yet of coronavirus cases in care homes in the UK.
They found that homes with fewer than 20 residents were at a 5 per cent risk of suffering an outbreak.
But in homes with between 60 and 80 residents, the chance of a cluster of cases spiked to between 83 and 100 per cent.
Large care homes inevitably have more staff, which increases the risk of infection being brought into the homes.
They also rely on agency workers who often work between different homes and therefore are exposed to a larger proportion of vulnerable residents.
Homes with a large number of residents also take in more visitors, who also drive up the risk of bringing the disease into the homes.
Professor Bruce Guthrie, director of the Advanced Care Research Centre at Edinburgh University and lead author of the report, told the Guardian: ‘More footfall will give you more risk of infection.
‘Although care home size cannot be altered without losing places for existing residents, there may be potential to create discrete units within care homes where smaller numbers of staff and residents are effectively cohorted to create self-contained units.’
The average care home in the UK houses around 35 residents. But HC-One, the largest British provider of private care homes, averages 50 beds, the Guardian reports.
Some 26 residents died at the firm’s 87-bed Melbury Court in Durham, while 22 passed away at the Highgate care home near Glasgow, which houses 80 residents.
HC-One admitted that high numbers of staff in larger homes increased the risk of infections occurring, but insisted it had highlighted ways to mitigate this.
Liz Whyte, the director of standards at the firm, said: ‘In a large service you can create smaller services, cohorting your staff and having a safe way of working with shared kitchen and laundry staff.
‘That is now in place. Until there is a cure, we have to work as if we are in an outbreak.’
It comes after Care England, which represents 4,000 providers, warned Boris Johnson must carry out his promise to fix the care crisis to prevent thousands of vulnerable residents being placed in danger.
In its letter, Care England states: ‘With a second wave on the horizon, it is imperative that the Government fixes the stark social care crisis now.
‘With such a large majority in Parliament, now is the time to put an end to all the past inertia and make changes.’
It is nearly a year since Mr Johnson promised to ‘fix the crisis in social care once and for all with a clear plan we have prepared to give every older person the dignity and security they deserve’.
Yet in the last 12 months neither Mr Johnson nor Health and Social Care Secretary Matt Hancock has revealed anything more about their plan.
Last week the Prime Minister provoked fury by implying care homes were responsible for their virus death toll by failing to follow correct procedures.
The letter insists: ‘It was outrageous to try to throw the blame for the tens of thousands of tragic care home deaths to the very people who have been striving to protect them. It is misleading and unfair to single out care providers when in reality the social care sector was abandoned to give priority to the NHS.
‘The failure to protect care homes has thrown the entire sector into disarray. There is no need for more consultation, inquiries, rhetoric and the like. We are fed up with procrastination; it is a crying shame that this pandemic has shown the nation just what an important sector we are, but we must seize this opportunity and make change or generations to come will never forgive us.’
Labour’s health spokesman Liz Kendall backed the letter from Care England, saying: ‘Boris Johnson promised to fix the crisis in social care and he must now step up to the mark.
‘Rather than blaming care homes and staff who have gone the extra mile to look after their residents, the Prime Minister should be taking responsibility for the Government’s actions and learning lessons from his mistakes.’
Caroline Abrahams, of Age UK, said the coronavirus crisis had exposed ‘the systemic failings that have bedevilled care for a long time’.
Fiona Carragher, of the Alzheimer’s Society, added that care homes and dementia sufferers had been ‘unforgivably abandoned’ during the pandemic.
A Government spokesman said: ‘We are doing all we can to support care homes.’ They stressed repeat testing had been introduced along with ‘significant’ funding, including £600million to boost infection control, and 156million items of personal protective equipment.’