LONDON - A technical glitch that caused nearly 16,000 Covid-19 cases to go undocumented in England was caused by some Microsoft Excel data files exceeding their maximum size, British Health Secretary Matt Hancock said.

The error "should never have happened", Mr Hancock told the House of Commons on Monday (Oct 5).

The health secretary was giving members of Parliament a rundown on how 15,841 positive coronavirus test results recorded between Sept 25 and Oct 2 were not reported in the country's daily figures - and, critically, were not passed onto the tracing programme.

Those who tested positive were informed of their results but were not then called by tracers - meaning anyone whom they had close contact with has also not received instructions to self-isolate. Scientific experts say that must happen within 48 hours for a test-and-trace programme to be effective.

Mr Hancock said there was a failure in the "automated transfer of files" from laboratories to Public Health England (PHE).

"This is a serious issue which is being investigated fully," he said. "This incident should never have happened. But the team have acted swiftly to minimise its impact."

PHE said the technical glitch, discovered overnight last Friday, had been fixed, and outstanding cases had been passed on to tracers by early Saturday.

But by Monday afternoon, around half of those who tested positive were still yet to be asked about their close contacts.

The Labour Party said the missing results were "putting lives at risk", with "thousands of people blissfully unaware they have been exposed to Covid".

HOW IT HAPPENED

The error was caused by some Microsoft Excel data files exceeding the maximum size after they were compiled, BBC reported.

PHE had set up an automated process to pull together text-based lists of data collected by commercial firms paid to carry out Covid-19 swab tests.

The data was compiled into Excel templates that were then uploaded to a central system and made available to the NHS Test and Trace team as well as other government computer dashboards.

But PHE developers picked an old file format, XLS, to do this. As a result, each template could handle only about 65,000 rows of data rather than the one million-plus rows that Excel is capable of.

Each test result occupied several rows of data, which meant that each Excel template was limited to only around 1,400 cases. When the total was reached, further cases were simply left off, according to the BBC report.

The technical error meant the number of new daily cases reported over the past week was lower than the actual number.

Daily figures for the end of the week were about 10,000 rather than the 7,000 initially reported.

BBC analysis found that the number of cases reported for the week to Oct 1 rose by around 93 per cent in the North West after accounting for the error - with similar rises reflected across England.

Britain's government coronavirus dashboard on Wednesday showed a total of some 530,000 Covid-19 cases reported to date and more than 42,000 deaths.

Additional reporting from Bloomberg