The Covid positive test rate in New South Wales has risen to 6.5%, the highest since the pandemic began.
The positivity rate is up from 1.73% a week ago and 0.71% a fortnight ago, a figure some epidemiologists say is likely to mean a proportion of cases are going undetected.
In the 24-hour period to 8pm on Sunday, 97,241 tests were conducted, with 6,324 cases detected, resulting in a positive test rate of 6.5%.
Prof Alexandra Martiniuk, an epidemiologist at the University of Sydney, said: “Early in the pandemic, the World Health Organization set 5% test positivity and below as the marker of having infections and transmission relatively under control.”
After the easing of restrictions in mid-October, the positive test rate hovered at 0.5% or below while testing numbers remained relatively high.
“Around 15 December our test positivity started to depart from the [roughly] 1% which we typically have in NSW,” Martiniuk said.
The timing of the uptick in test positivity corresponded with the lifting of restrictions in conjunction with the arrival of the Omicron variant and holiday socialising.
“When there is a high test positive rate, the number of confirmed cases is likely to be only capturing some of the true number of cases.”
Provided testing turnouts are consistent, the higher the positive test rate climbs, the greater the extent of undetected spread of Covid.
While the state has recorded its highest positive test rates since the start of the pandemic, Martiniuk said it was important to keep in mind the slightly lower testing numbers over the Christmas weekend.
Head of the University of Melbourne’s school of population and global health, prof Nancy Baxter, said while the increased positive test rate did indicate a level of undetected viral spread, it was difficult to know the extent.
“It does however mean people are using the service appropriately. The increase in positivity is not consistent with the narrative that inappropriate or unnecessary testing is what’s driving the long lines,” Baxter said.
Baxter also said an increase in the positive test rate could be due in part to rapid antigen tests having detected asymptomatic cases, which were then confirmed by PCR tests.
Testing facilities across the state have been overwhelmed in the face of the outbreak; patients are routinely waiting 72 hours to receive results, with some reporting waiting times of well over 100 hours.
100 hours down & still waiting for a result. Entire household in lockdown attempting to do the right thing. But 4 days+ and no result and no answer at the only number provided. Hey #Histopath@Dom_Perrottet@NSWHealth@BradHazzard does this look like a system that works to you?
— Princess Mattie (@PrincessMattie1) December 27, 2021
119 hours! 4cyte results are n.e.g.a.t.i.v.e #covid#allowedoutpic.twitter.com/iBLueiPXVj
— OFoibles (@nat_ofoibles) December 27, 2021
On Sunday it was revealed that more than 400 patients who had been swabbed from 22 to 23 December had been mistakenly sent negative test results. St Vincent’s hospital in Sydney was forced to issue an apology; the medical director of SydPath, the hospital’s pathology service, prof Anthony Dodds, attributed the mistakes to human error.
On Monday the pathology lab announced another 995 people had been prematurely sent negative test results while the actual results were yet to be determined. The hospital said the additional results would be delivered by Monday night.
Despite the increased positivity rate, Martiniuk says NSW’s testing levels are “very good”. In Malawi, where Martiniuk has worked, test positivity has remained “comparatively high” due to lower testing levels.
In Ontario, Canada, with a population double that of NSW, about 70,000 tests are being carried out a day, or roughly half of NSW’s tests before Christmas Day. There, the positive test rate is 18.7%.
Martiniuk emphasised the ongoing importance of testing in slowing and reducing the spread of Covid infections.
“Testing will help us understand the potential load on hospitals and primary care.”
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