McMaster study shows one per cent of air passengers test positive for COVID within 14 days
Preliminary results from a large Hamilton-led study show that one per cent of air travellers who landed at Toronto's Pearson airport from international destinations in September tested positive for COVID-19 within 14 days.
The study by McMaster HealthLabs found 89 passengers out of 8,644 who took part tested positive for COVID either immediately upon arrival, at the seven-day mark, or at the 14-day mark. It's the largest study of its kind conducted in the world.
About 70 per cent of the positive results - roughly seven out of every 1,000 passengers - were detected upon arrival at the airport. Most of the remaining cases were detected at the seven-day mark of quarantine. Just five of the 89 positive cases were detected at the 14-day mark of quarantine.
The study's findings could have implications for the amount of time international air passengers have to spend in quarantine when they arrive in Canada.
In Ontario and most of Canada, travellers arriving in the country from international destinations must quarantine in-house for 14 days.
What we're trying to understand is whether developing COVID after day seven is common enough that it justifies everybody going into 14 days of quarantine," said Dr. Marek Smieja, scientific director of McMaster HealthLabs and a professor of pathology and molecular medicine at McMaster University.
The bad news is that there are some people where we first detect COVID after day seven," he said. The good news is that's a pretty rare event."
McMaster HealthLabs is a non-profit organization created by the university for COVID-related research.
Participants in the study were shown how to conduct their own oral-nasal swabs and agreed to test themselves three times - upon arrival at the airport, seven days into quarantine, and 14 days into quarantine.
The results are from tests conducted from Sept. 3 to Oct. 2, the first month of what was a two-month study.
There were a number of dropouts during the study, which is not unusual for a longitudinal experiment that tracks people over time. From the original 8,644 participants, about 6,600 submitted tests at the seven-day mark and about 5,500 tested themselves at the 14-day mark, which raises the possibility there may have been other positive COVID cases that weren't captured.
The study also makes the assumption the infections detected after seven and 14 days were acquired prior to travel and not picked up after the travellers landed in Canada.
By law they're in 14 days of quarantine so they're not meant to be going out," said Smieja. Of course, there could be a family member who's not in quarantine."
Smieja said he hopes the data will lead health experts to consider shortening the quarantine period to seven days for international air travellers.
Alberta has tried a smaller pilot study where air travellers were tested on arrival and after seven days.
The other question we pose is if seven people in 1,000 are travelling with detectable COVID, is there a better way of detecting those people before they get on an airplane?" Smieja said. Should people be tested prior to international flights? Would that make flying safer or not?"
Final results from the study, with a total of more than 16,000 participants, will be released in January.
Steve Buist is a Hamilton-based investigative reporter at The Spectator. Reach him via email: sbuist@thespec.com