The health secretary has said a technical glitch that saw nearly 16,000 Covid-19 cases go unreported in England “should never have happened”.
The error meant that although those who tested positive were told about their results, their close contacts were not traced.
By Monday afternoon, around half of those who tested positive had yet to be asked about their close contacts.
Labour said the missing results were “putting lives at risk”.
Experts advise that ideally contacts should be tracked down within 48 hours.
The technical error was caused by some Microsoft Excel data files exceeding the maximum size, and issues in the transfer of data between NHS Test and Trace and Public Health England.
It meant 15,841 cases between 25 September and 2 October were left out of the UK daily case figures, according to PHE.
PHE said the error itself, discovered overnight on Friday, has been fixed, and outstanding cases had been passed on to tracers by 01:00 BST on Saturday.
But Health Secretary Matt Hancock told MPs the incident as a whole had not yet been resolved – with only 51% of those whose positive results were caught up in the glitch now reached by contact tracers.
He said it had “not substantially changed” the government’s assessment of the epidemic and had “not impacted the basis on which decisions about local action were taken”.
He also said outbreak control in care homes, schools and hospitals had not been directly affected, as they do not rely on the data in question.
“This incident should never have happened. But the team have acted swiftly to minimise its impact,” he added.
The BBC has confirmed the missing Covid-19 test data was caused by the ill-thought-out use of Microsoft’s Excel software. Furthermore, PHE was to blame, rather than a third-party contractor.
The issue was caused by the way the agency brought together logs produced by the commercial firms paid to carry out swab tests for the virus.
They filed their results in the form of text-based lists, without issue.
PHE had set up an automatic process to pull this data together into Excel templates so that it could then be uploaded to a central system and made available to the NHS Test and Trace team as well as other government computer dashboards.
The problem is that the PHE developers picked an old file format to do this – known as XLS.
As a consequence, each template could handle only about 65,000 rows of data rather than the one million-plus rows that Excel is actually capable of.
And since each test result created several rows of data, in practice it meant that each template was limited to about 1,400 cases. When that total was reached, further cases were simply left off.
Until last week, there were not enough test results being generated by private labs for this to have been a problem – PHE is confident that test results were not previously missed because of this issue.
And in its defence, the agency would note that it caught most of the cases within a day or two of the records slipping through its net.
To handle the problem, PHE is now breaking down the data into smaller batches to create a larger number of Excel templates in order to make sure none hit their cap.
But insiders acknowledge that their current clunky system needs to be replaced by something more advanced that does not involve Excel.
Labour’s shadow health secretary Jonathan Ashworth said the missing results were “putting lives at risk”.
He said the unreported cases meant as many as 48,000 contacts had not been traced and therefore not been isolating, with “thousands blissfully unaware they’ve been exposed to Covid, potentially spreading this deadly virus”.
On Monday afternoon, the government’s coronavirus dashboard said that there had been a further 12,594 lab-confirmed cases of coronavirus in the UK, bringing the total number of cases in the UK to 515,571.
Another 19 people were reported to have died within 28 days of testing positive for Covid-19.
The earlier technical error meant the daily case totals reported on the government’s coronavirus dashboard over the past week have been lower than the true number.
- Why using Excel caused Covid-19 tests to be lost
- What’s the danger of the missing 16,000 Covid cases?
BBC health editor Hugh Pym said daily figures for the end of the week were “actually nearer 11,000”, rather than the roughly 7,000 reported.
BBC analysis found the number of cases reported for the week to 1 October increased by 92.6% in the North West after taking in the missing tests – with similar rises reflected across England.
The increase, of 8,348 cases, is mostly down to the missing tests, but the figures also included some results which came back after 2 October.
About 10,000 new cases a day, a figure that has doubled in a fortnight
You can look at the case numbers two ways: we normally count them on the date they’re reported, which today would be 12,594.
But today’s news has shown how reporting lags can skew those trends.
If you arrange the figures by the date the tests were taken you can get a clearer picture.
In that analysis, we reached an average of 10,000 new cases a day towards the end of last week.
That’s about double what it was a fortnight ago.
It’s hard to say for sure what’s happened since then since it takes a few days for tests to be reported and for these figures to settle down.
But that pattern is consistent with other data: the number of people going into hospital or official surveys and symptom trackers.
They all paint a picture of an epidemic that’s growing – not doubling every week, but growing.
There’s hope in some parts of the data that the pace of growth may be slowing slightly, but there’s no evidence that it’s shrinking.
PHE said NHS Test and Trace has made sure there are enough contact tracers working, and is working with local teams to ensure they also have sufficient resources to be urgently able to contact all cases.
The number of call attempts is being increased from 10 to 15 over 96 hours.
From 25 Sept to 2 Oct
50,786 Cases initially reported by PHE
15,841 Unreported cases, missed due to IT error
8 days of incomplete data
1,980cases per day, on average, were missed in that time
48 hoursIdeal time limit for tracing contacts after positive test
Source: PHE and gov.uk
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