Rapid testing identifies 70 per cent of COVID-19 positive passengers within 48 hours of arriving at airport: study

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TORONTO — The interim results from a Canadian border study has found that 70 per cent of international travellers arriving by airplane who have COVID-19 can be identified within 48 hours through rapid PCR testing done the moment they arrive.

A very small percentage of travellers only tested positive for COVID-19 a full 14 days after arriving, with just under 30 per cent testing positive after seven days.

"We wanted to look at what the risk of travellers coming into Canada bringing COVID is," Vivek Goel, a professor with the University of Toronto and one of the study's principal investigators, told CTV News.

"We tested people on arrival, day seven and day 14. So as far as we know we're the only group to have data of this size -- over 10,000 travellers -- who have been tested at all three time points, and we can then determine if you reduce the quarantine with a test protocol, how many cases you might miss if you were to allow people out [of quarantine], say after seven days or after one day."

The study, run by McMaster Health Labs (MHL), was first launched in September at Pearson Airport in Toronto and continued until Nov. 14. Passengers arriving on Air Canada or select Star Alliance flights were asked if they were willing to participate in a study that involved taking a PCR test at the airport, and then two follow-up tests at home a week and two weeks later, while they were in the mandatory two-week quarantine.

Although the final report will be based on more than 16,000 participants, the interim results track the first month of the study, from Sept. 3 to Oct. 2, and involve more than 8,600 participants.

These results found that 99 per cent of participants tested negative for COVID-19. Of the one per cent who tested positive, 70 per cent tested positive after their very first test, and knew within 48 hours.

"A very small fraction are left and detected on day 14," Goel said. He said these individuals could be falsely positive or be residual cases who are not actually infectious, or could have failed to comply with quarantine and thus have caught COVID prior to leaving the airport.

"Or they could truly be people with the very long tail of the incubation period," he said. "But the key finding is that [a] testing strategy, particularly one that picks people up on day one, and day seven like Calgary is doing, will get the vast majority of people [who] are likely infectious."

Since the beginning of November, a pilot project being run through the Calgary International Airport has been offering rapid tests at the airports. The project gives travellers the option to get a test and isolate for 24 to 48 hours while waiting for their results. If they test negative, they do not need to self-isolate for the full two weeks, as long as they agree to stay within the province for that time period.

Goel pointed out that there are precautions in the Calgary pilot project.

"People are checked in every day by the local public health authorities, they're asked not to go to congregate living settings or visit peoples that are vulnerable to higher risk, but they're not asked to restrict themselves for 14 days either."

Many countries test people before they board an airplane in the first place, and some require tests upon landing, Dr. Marek Smieja, MHL scientific director and co-author of the study, told CTV News.

In Canada, there's no requirement for testing before getting on an airplane, and outside of pilot projects, no tests offered after you come off of one, Smieja said.

"Increasingly, especially for international flights there's an interest in screening people before they get on an airplane," he said. "And secondly, there's interest in asking, ‘Can quarantine be shortened if the testing shows that you have not developed COVID by perhaps seven days?'

"Our quarantine is 14 days and that's based on the maximum incubation time for COVID. Therefore we wanted to study it throughout the 14 days to ask the question, ‘Do we really need a full 14 days of quarantine?'"

International travel was how COVID-19 first entered Canada, but at this stage in the pandemic, most of the viral transmission is within the country. But that doesn't make it any less important to understand the risks of international travel and reopening the borders.

As Canada faces a second wave of COVID-19, nine months into the pandemic, the pressure to allow more travel builds for policy makers and officials.

"We can't not have any travel for prolonged periods of time, so it's a matter of trying to find how can we safely live with COVID for some period of time," Smieja said.

The two-week quarantine is a huge deterrent against traveling Goel said, adding that there are "economic, social and psychological costs from having to be in the quarantine."

Smieja pointed out that many two-week quarantine also can interfere with work for many.

"The ultimate message is that there are ways of reducing the quarantine requirement with testing protocols," Goel said.

The final report for the study will be available in January 2021.

SELF-ADMINISTERED TESTS

The study also proved the feasibility of using rapid PCR testing in an airport setting, researchers say.

The study used a cheek and nasal swab that could be self-administered, meaning that, crucially, a health-care worker was not needed and people could take the test at home, which they did on day seven and day 14 of the study.

"We had a courier go and pick it up from them," Goel explained. "So it shows that people can do self-collection, and we can get it done at the home."

Smieja said that the tests were processed in a laboratory after being retrieved, and "only about one to two per thousand were very low quality where we couldn't interpret it," showing the majority of people were able to follow the instructions to do the tests at home.

Goel pointed out that needing a healthcare worker to administer tests is part of the reason big lineups have been seen at testing facilities.

"Then those health care workers that are doing more testing at the assessment centres are being taken away from other parts of the healthcare system, and that PPE is being taken away," Goel added.

Testing is hugely important, and the testing capacity in Canada needs to be increased if we want to ever get control of COVID-19 again, Goel said.

"We should have more testing for health-care workers, should have more testing for grocery store workers and people on the front lines."

He said researchers believe that the rapid testing capable of being performed at home could be used in schools and workplace setting, for "surveillance testing."

If a person is displaying symptoms, it makes more sense for them to go to a healthcare worker to receive the standard test, he explained, but if we were able to test in other settings on a more efficient basis in order to find cases before people even suspect they have the virus, that could help reduce wait times for tests at hospitals, and also free up staff.

"If we'd have [had] more testing capacity in place back in late August, we would have not been, [where] we're at now," Goel said. "So what I would say is if -- when -- we come out of this next wave, we really have to think about building up testing capacity so we don't get back here. And then we'll have testing capacity to open up the border when we're ready.

"A number of provinces including Ontario [have] been experimenting with alternative selection methodologies," Goel said, adding that he's "hopeful" this type of testing could be used more in the future.