Saliva test as accurate as the gold standard

Toronto scientists say they've developed a new, saliva-based test for the COVID-19 virus whose precision and ease of use could make it a “game changer” in combating the pandemic.

The antigen test requires subjects to simply spit out a sample, needs no health worker to administer an uncomfortable nasal swab and could be processed relatively quickly in a mobile laboratory, say the researchers at Mount Sinai Hospital's Lunenfeld-Tanenbaum Research Institute.

Perhaps most crucially, their initial trial run on saliva samples from known COVID patients suggests the test is as accurate as the gold-standard PCR technology used most commonly in Canada.

With an ability to test hundreds of people per hour using minimal staff — and producing results in one to four hours — it could be easily deployed to screen individuals without symptoms, such as school staff and students or employees at a factory, they say.

The test is still in the experimental phase, and the first small study was posted on a “preprint” site without peer review.

But if the early results are validated, it would offer a novel addition to the arsenal of non-PCR testing options that many experts say should be used much more widely to get ahead of the virus's spread.

“This assay can be a game changer,” predicted study author Eleftherios Diamandis, a Mount Sinai medical biochemist and University of Toronto professor.

“There is a big information gap, and we need tools to really address this gap,” said co-author Ioannis Prassas, a scientist in Diamandis's lab. “We don't have the amount of information required to maximize our responses to the pandemic.”

Meanwhile, a separate Canadian company is unveiling another testing innovation that it also predicts could have a significant impact.

Fredericton, N.b.-based Luminultra said its GeneCount system uses PCR technology, but the samples can be tested on site with mobile equipment, rather than needing a centralized lab. results are available in less than two hours, it said in a statement Wednesday.

The test will be used starting March 1 in a federal research project at Pearson International Airport.

So far in the pandemic, Canada has mostly employed polymerase chain reaction (PCR) tests, designed to detect genetic evidence of SARS -COV-2, the virus that causes COVId-19 disease. It's the most accurate technology available. but the assays require a health-care worker to administer a nasal swab and have to be processed in busy labs, sometimes with results delayed a day or more.

The chief alternatives now are rapid tests that seek out antigens, the virus proteins that trigger the body's immune system. They're less precise but can be administered almost anywhere and processed in as little as 15 minutes, though usually still require nasal swabbing.

Saliva tests have a key advantage, allowing individuals to readily and comfortably provide samples on their own. but saliva contains only small amounts of virus, and the accuracy to date has been relatively low, said diamandis.

A university of Ottawa study published last month found PCR testing using saliva samples was useful, though did not catch as many cases from the same group of subjects as swabbing.

diamandis and Prassas typically study cancer-related issues. but pivoting to COVID, they collaborated with Meso Scale diagnostics, a Maryland-based company, to develop a technique for antigen testing of SARS-CoV-2 that uses “electroluminescence” — light generated by a strong electrical current — to increase precision.

They assessed the system's effectiveness on saliva samples provided by 90 COVId patients from Toronto-area hospitals, and 15 controls not known to be infected.

The results of the blinded experiment were similar to that of PCR tests, they reported.

A larger study with 1,000 samples is underway and should be completed by mid-April, while discussions with companies interested in commercializing the technology are already underway, said diamandis.

The group's system would not be as fast as the current rapid antigen tests. The results now take three to four hours to complete, though the researchers hope to reduce that to one to two hours.

but a mobile lab could be taken to schools, nursing homes or workplaces in the back of a minivan, providing relatively quick and very accurate tests, said Prassas.

Other experts have said even less-precise rapid tests should be deployed widely to screen people without symptoms and proactively identify potential outbreaks. The federal government has provided 38 million rapid tests to the provinces, though relatively few have been used.