Experts urge caution in reading rapid tests as variants drive sixth COVID wave

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Speedy antigen checks have turn out to be Canada’s major instrument to detect COVID-19 as mounting indicators level towards a sixth wave, however consultants warn that outcomes must be learn with warning because the unfold of variants raises questions on diagnostic accuracy.

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The pinnacle of Ontario’s science advisory panel forecasted a COVID-19 “tidal wave” as wastewater monitoring means that the province is seeing between 100,000 and 120,000 new infections every day.

That’s a far cry from the 4,224 instances formally reported Thursday due to restricted PCR testing.

Hospitalizations in Ontario are up 40% week over week, with 1,126 individuals reported hospitalized with the virus and 159 in intensive care.

In the meantime, Quebec well being officers reported 3,777 new COVID-19 instances based mostly on PCR testing, and 1,582 individuals in hospital with the illness.

Ontario and Quebec are among the many provinces which were reporting artificially low confirmed case counts since limiting entry to PCR testing throughout the first Omicron wave.

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Whereas fast antigen checks have been exhausting to come back by throughout the variant’s preliminary rise, provide has elevated as Omicron’s extra contagious sibling, the BA.2 subvariant, appears to gasoline one other surge.

Well being Canada mentioned 261 million fast checks have been distributed from Dec. 4 to Feb. 28, in comparison with practically 90 million within the earlier two months.

Whereas fast checks can assist Canadians make safer choices about the way to navigate this rise in infections amid loosening of public well being measures, consultants warn that they will additionally present a false sense of safety.

Dr. Christopher Labos, a Montreal heart specialist with a level in epidemiology, mentioned it takes multiple fast check to rule out an infection due to excessive charges of false negatives.

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Potential sources of inaccuracy embrace improper method and testing too early within the sickness for viral ranges to be detectable, mentioned Labos.

There are research that counsel repeated fast testing at frequent intervals can enhance detection, mentioned Labos. So in case your first fast check comes again destructive, check once more, he steered.

“Now that we’re into the ‘choose your individual danger’ part of the pandemic … I feel individuals want to appreciate that the chance of false negatives with fast checks could be very actual,” Labos mentioned, noting that proof suggests the speed of false positives is pretty low.

“If you happen to take your destructive outcome as a license to return to regular, you is perhaps inadvertently infecting different individuals, so I’d proceed to isolate, repeat the testing and make very positive you don’t have COVID.”

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There are additionally questions on whether or not fast checks are much less delicate to Omicron subvariants.

Well being Canada mentioned it’s monitoring rising variants carefully and present proof suggests agency-approved checks proceed to be efficient. Additionally, it mentioned, producers should notify Well being Canada if their checks are affected by a variant.

In February, the Ontario COVID-19 Science Advisory Desk printed findings from an evaluation of preprint research suggesting that the pooled sensitivity of fast antigen checks for detecting Omicron infections is about 37%, in comparison with 81% for the Delta variant.

The science desk’s director, Dr. Peter Juni, mentioned he hadn’t appeared into whether or not fast check sensitivity differs between the 2 Omicron subvariants, however he expects extra knowledge will quickly emerge.

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He supplied a rule of thumb for deciphering a fast check outcome: if it’s optimistic, consider you have got COVID-19, but it surely takes at the very least two destructive checks roughly 48 hours aside to substantiate you’re within the clear.

Whereas many fast check kits direct customers to solely take a nasal pattern, Juni mentioned swabbing the cheeks and the again of the throat beforehand might result in extra dependable outcomes.

However Omar Khan, a professor of biomedical engineering and immunology on the College of Toronto, strongly discouraged veering from the check equipment’s directions, noting that the units have been designed and accredited based mostly on the really useful methodology of use.

Khan mentioned fast checks are an vital, if imperfect, instrument to information particular person behaviour, however their public coverage purposes are restricted.

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Many provinces don’t have techniques to gather fast check outcomes, and those who do depend on voluntary reporting, which skews the information.

Khan mentioned authorities must bolster their efforts to trace how COVID-19 is spreading and mutating as a result of because the virus continues to evolve, our present screening strategies might turn out to be much less efficient.

“The targets of those fast checks are now not legitimate (if) genetically it’s modified an excessive amount of. And that’s going to be vital as a result of we need to ensure we’ve the precise instruments for surveillance and detection of the pathogen.”

Juni mentioned limits on PCR testing make it unclear how lengthy this wave will final as a result of we don’t understand how many individuals have been contaminated to this point and will have an additional little bit of immunity.

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His feedback come as all three of Ontario’s opposition events known as on the federal government to reinstate or proceed a number of public well being measures, together with obligatory masking and better entry to PCR testing.

Ontario Well being Minister Christine Elliott, citing the province’s chief medical officer of well being, Dr. Kieran Moore, mentioned the province needn’t reintroduce masks mandates as a result of an increase in instances was anticipated.

On the East Coast, Nova Scotia officers additionally mentioned there have been no quick plans to re-introduce measures equivalent to obligatory masking, regardless of a big soar in confirmed COVID-19 instances.

Alberta well being officers cautioned that COVID-19 transmission seems to be on the rise with positivity charges and wastewater knowledge trending upward. Well being Minister Jason Copping mentioned the province isn’t contemplating bringing again public well being measures.

Saskatchewan’s high physician mentioned the province is experiencing a resurgence of instances that might final till mid-Could or early June earlier than instances begin to degree off.

In the meantime, Manitoba’s chief public well being officer mentioned there are indicators of accelerating COVID-19 transmission, however extreme outcomes have plateaued.

— With recordsdata from Nicole Thompson in Toronto, Keith Doucette in Halifax and Steve Lambert in Winnipeg