Metric loss

Number of self-reported Covid cases now ‘unreliable metric’ – epidemiologist

The rise of self-reported rapid antigen tests (RATs) for Covid-19 has rendered daily case count data almost completely unusable, according to University of Auckland epidemiologist Professor Rod Jackson.

“I think we’ve lost total control of the number of cases,” he said. “We have lost an important source of data that could help us in our planning. And I think it’s too late to get it back.

People who test positive for RAT should report their results on My Covid Record or by phone, but it’s impossible to know how many people neglected to do so.

There were 17,522 new community cases of Covid-19 announced by the Department of Health on Monday.

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Epidemiologist Professor Rod Jackson said the self-report RAT tests meant some data was less reliable.

RICKY WILSON/Stuff

Epidemiologist Professor Rod Jackson said the self-report RAT tests meant some data was less reliable.

This is down from the peak of more than 23,000 cases last week, it is possible that this is due to more people using self-administered RATs rather than PCR tests.

Jackson said the new self-reporting system meant daily case counts were no longer a reliable measure.

That meant it was much harder for modelers to track the spread of the virus and predict its peak.

“We just have no idea what that means. It would take a major jump in cases or a major drop for that to mean anything – many thousands. It would almost take [a change of] five to ten thousand for it to make sense,” he said.

Chief Health Officer Dr Ashley Bloomfield said the vast majority of new cases came from self-reported testing.

ROBERT KITCHIN/Stuff

Chief Health Officer Dr Ashley Bloomfield said the vast majority of new cases came from self-reported testing.

This means hospitals and other healthcare providers have a much less effective warning system in place to help them prepare for a surge of patients.

“It’s very, very helpful to have this data to help you plan. And when we switched to self-administered RATs, we lost that signal.

He said he would have preferred the Department of Health to put in place a system where RAT tests were readily available but administered and recorded by trained professionals, like in a pharmacy.

At a press conference last week, Chief Health Officer Dr Ashley Bloomfield played down the risks of inaccurate RAT test numbers.

People can order RATs from a website set up by the Department of Health if they meet certain criteria.  (File photo)

LIBBY WILSON/Stuff

People can order RATs from a website set up by the Department of Health if they meet certain criteria. (File photo)

He said about 85% of newly reported cases are identified from RAT tests.

“My feeling is that if people are motivated enough to go out and take a RAT test, they’ll generally be motivated to record that result,” Bloomfield said.

Professor Michael Plank, of Te Pūnaha Matatini and the University of Canterbury, said broader trends could still be determined from the numbers, but it was becoming more difficult.

“If we start to see an upward trend in cases or a downward trend in cases that is consistent over a period of a week or more, that tells you something about the growth or decline in cases,” said he declared.

A clearer picture of the current number of cases could emerge by the middle of the week.

“We know that fewer people generally go out and get tested on the weekends, so the numbers for Sunday and Monday largely reflect people who were tested on the weekends, so we expect them are down. We have to wait for the numbers from Tuesday and Wednesday to get anything out of it. »

How to self-report RAT test results

Anyone in New Zealand aged 12 or over can connect to the My Covid file website and select “Self-report a Rapid Antigen Test (RAT) result” or “Report a test result”.

You will then be asked to enter your mobile number, and to indicate which lines are visible on your test.

You can also report a test result yourself over the phone by calling 0800 222 478 and choosing option 3.