A large contingent of coronavirus carriers in Manitoba is undiagnosed and unknowingly spreading the contagion in the community as test positivity rates reach heights never before seen in the province’s pandemic curve.
On Thursday, the five-day test positivity rate for the province was 14 per cent, a figure that has grown rapidly during the past 10 days, after steadily climbing since early October.
Considering the high positivity rates, Tara Moriarty, an infectious diseases expert and associate professor at the University of Toronto, said Manitobans should be extremely careful. They should consider that everyone they come into contact with in the community — and even themselves — could be carrying the virus.
"It’s not possible right now for these public health response systems to accurately identify cases and there are probably an enormous number that are being missed," Moriarty said Thursday.
"So the best thing people can do right now is through their own behaviour, limit their contacts with other people as much as possible, and that’s the best thing for slowing down the epidemic."
In the past seven days, the province has reported more than 2,600 new infections, including 475 on Thursday.
Meanwhile, public health officials say that at least 500 cases in the past week have no known transmission chain, meaning the infection can’t be linked to a specific person, event or place.
Through seroprevalence surveys, which look for COVID-19 antibodies in blood, Moriarty said jurisdictions that reported high test positivity rates in the first wave of the pandemic estimate the actual number of infections to be much higher than initially reported.
"It would be universally acknowledged that at 14 per cent (test positivity), you are absolutely not capturing probably at least 80 to 90 per cent of infections," Moriarty said.
"The epidemic is much bigger than you think," she said. "Right now, I would guess that the only option — whether they call it a circuit-breaker or a lockdown — you just have to stop people being close to each other as much as possible."
Chief provincial public health officer Dr. Brent Roussin unveiled stricter public health measures on Thursday, as he announced that eight more Manitobans had died. Just a week earlier he had put in place critical-level restrictions.
"The test positivity is too high. We can’t sustain this," Roussin said.
"When you have a high test positivity, that means it’s increasing the likelihood that when you’re in a group of people, someone in there is infectious."
As of 12:01 a.m. Friday, retailers deemed to be critical will no longer be permitted to sell non-essential goods in-store and people will be prohibited from having others over to their house, with exceptions for health-care, home care, child care, tutoring, deliveries, and for those who live alone.
Daniel Coombs, a professor of mathematics at the University of British Columbia and an epidemic modelling adviser to the British Columbia Centre for Disease Control, said when a test positivity rate hits double digits, it raises questions about testing capacity and access, and should be taken as a warning that testing is limited.
"There’s always people who have COVID but they don’t seem to have any symptoms. They don’t feel unwell, or their symptoms are super mild and they don’t get tested," Coombs said. "We know that testing is always an underestimate and it can be by a pretty good fraction.
"Back when testing was really limited here in B.C., the estimate was more like we were catching maybe one in five, or one in 10 of the actual true infections through the testing," he said.
On Thursday, 3,269 swabs were processed at labs in Manitoba and for the time being, testing is being prioritized for people who have symptoms of COVID-19.
The Winnipeg Regional Health Authority said community screening sites in the city haven’t reached capacity since Oct. 6. A spokesperson for the province said as of Thursday, with the exception of the drive-up site at 1181 Portage Ave. in Winnipeg, all testing sites across the province were able to offer tests that day.
James Blanchard, a professor in community health sciences at the University of Manitoba, said it is hard to say just how many cases may go undiagnosed, as little information about testing patterns is shared by the province.
"But I would reiterate that 14 per cent is high — whichever way you slice it," Blanchard said.
"The test positivity rate has been going up for quite some time now. The issue is, once it’s been going up, it really indicates that there’s quite a bit of epidemic momentum, and it’s much harder to slow that down and reverse that."
Roussin said capacity for COVID-19 screening is good at the moment, but too much transmission of the virus continues to occur.
The World Health Organization says the test positivity rate should remain below five per cent for at least two weeks before governments should consider relaxing restrictions.
"The effectiveness of the orders in place thus far, they may have been effective, we may have seen numbers much higher than this but for them," Roussin said. "But they’re certainly not taking us to where we need to be, and that’s why we had to put these additional measures in."
Danielle Da Silva
Danielle Da Silva is a general assignment reporter.