Cautious welcome for rapid antigen tests to control Sydney Covid outbreak, despite reliability concerns
Reviews of rapid Covid-19 tests in Australia have found markedly different results in their effectiveness, but experts say the New South Wales government’s decision to employ them in schools and essential workplaces will help to control the virus.
As NSW recorded 177 cases of Covid-19 and extended its lockdown for another four weeks on Wednesday, the premier, Gladys Berejiklian, indicated that rapid antigen testing was likely to be used in schools by the middle of August to allow year 12 students to begin returning to classrooms before end-of-year exams.
The premier indicated the state’s health department would also work with business with a view to introducing the rapid tests in workplaces such as construction sites.
Rapid antigen testing, which has been widely used in countries such as the UK, are able to return results within 15 to 30 minutes. They are already used in a limited form in some Australian workplaces, such as film production.
But their widespread use has been restricted because they are not as reliable as the polymerase chain reac
tion (PCR) tests which have formed the backbone of Australia’s response to Covid-19.
Part of the resistance to their use has come from the Royal College of Pathologists of Australasia, which last week issued a statement reaffirming their opposition to the use of rapid testing in low prevalence settings of the virus.
“We are becoming increasingly concerned at the level of commentary that promotes rapid antigen tests for the detection of Covid-19, despite the evidence,” Dr Michael Dray, president of the RCPA, said in a statement.
“When put into real-world settings, the evidence shows that there are significant differences between the actual performance of rapid antigen tests and manufacturers’ claimed test performance.”
Rapid tests had “a relative increased chance of giving both false negative and false positive results” compared with PCR tests, the statement said.
Catherine Bennett, an epidemiologist at Deakin University, said results from rapid antigen tests were “quite variable depending on which tests you’re looking at”, ranging from 60% to 90% reliability.
Last month the US Food and Drug Agency found that the tests used by the million in Britain’s mass testing program were a risk to health and should be thrown away, or returned to the manufacturer.
NSW Health has not said which tests would be used in its program, but Melbourne University’s Doherty Institute has analysed the reliability of a series of rapid tests approved by the Therapeutic Goods Administration throughout the pandemic.
In April last year an analysis of two different rapid testing products approved for use found their performance was “below that reported by the manufacturer” and the report recommended they “should not be used in the diagnosis of acute Covid-19”.
Another report, in September last year, found the effectiveness of the tests reviewed “vary markedly depending on the point-of-care tests assessed, and most often fall below that reported by the manufacturer in the instructions for use”.
However by February this year, another study of five tests suggested all “demonstrate specificity similar to that reported in the manufacturers claim”.
And as Sydney’s outbreak worsens, epidemiologists and politicians have begun to call for the use of the tests in certain settings.
Bennett said that at the beginning of the pandemic rapid testing was “just not accurate enough to play a role”. While the accuracy of the tests was “still quite variable” depending on the product, she believed they could be used in contexts where testing was “targeted and repeated”.
“The idea is if you need really quick tests and you’re going to do it often, they offer one possibility because it’s easy to screen people and get that result,” she said.
“You do run the risk that you will miss cases [but] if you target them to the areas you want most – so at schools and work sites every day – if you miss one, you’re more likely to pick it up the next day.
“As with everything we talk about in this space nothing is a guarantee and so you put partial guarantee over partial guarantee and you get layer upon layer of certainty.”
Support for the tests has gained support across the political spectrum. Coalition backbencher and paediatrician Katie Allen has expressed her support for their increased use, as has the Labor MP and doctor Mike Freelander.
This week Freelander wrote to the federal health minister, Greg Hunt, and NSW health minister, Brad Hazzard, calling on them to adopt rapid testing in places such as workplaces and schools.
“Such a system would have bipartisan support and would be an important tool in management of the pandemic,” he wrote.
In her press conference on Wednesday, Berejiklian acknowledged the tests were “not as accurate” as PCR.
“We accept that it’s not as accurate as other types of testing but at least it does give us an indication of where cases might be,” Berejiklian said.
“I understand it is more likely to provide a positive test than not, which is not a bad thing.”