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Coronavirus: B.C. positivity rate ‘concerning’, but threshold for restrictions not useful, says SFU epidemiologist

Click to play video: 'Vancouver data analyst believes B.C. COVID-19 positivity rate closer to 10%' Vancouver data analyst believes B.C. COVID-19 positivity rate closer to 10%
WATCH: B.C.'s top doctor stands by the BC Centre for Disease Control data when it comes to the province's COVID-19 positivity rate but as Aaron McArthur reports, mathematicians say one industry's mass testing may be throwing the numbers off balance – Nov 16, 2020

A mathematician and epidemiologist at Simon Fraser University says she’s watching BC’s COVID-19 positivity rate closely — but it may not be a good comparison against places like New York, which has implemented harsh restrictions, including closing schools, after crossing a threshold of 3 per cent positivity.

B.C.’s seven-day rolling average positivity rate has been hovering around 6.6 per cent as of Nov. 17, with Fraser Health at 9.4 per cent and Vancouver Coastal Health at 4.8 per cent, according to data from the BC Centre for Disease Control.

Caroline Colijn told Global News those numbers are definitely cause for concern, but it’s tough to compare with places like New York, which has been testing people at a far higher rate than B.C.

“If they’re testing far more asymptomatic individuals than we are, then 3 per cent might be sort of high for them and it may not be as high for us,” she said.

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Read more: While COVID-19 surges, health officials cautiously optimistic seasonal flu cases dropping

And Colijn doesn’t think B.C. should follow suit in implementing a positivity threshold to induce more restrictions.

“I just don’t think you want to put too much weight on it. You don’t want to have it under political pressure to go down,” she said.

“Because we know ways to make it go down, right? We can start including vast armies of people who have a low likelihood of testing positive and it will go down, but that’s not what we want to do.”

Read more: Multiple B.C. film and television productions paused amid COVID-19 testing crunch

In fact, Colijn said that’s actually happening in one way already — with private tests conducted for members of the film industry in B.C. being concluded in daily provincial numbers. Colijn said people in those industries are being tested multiple times a week and are far more likely to test negative.

But that drives our positivity rates lower than they should be, Colijn said.

Click to play video: 'Vancouver data analyst believes B.C. COVID-19 positivity rate closer to 10%' Vancouver data analyst believes B.C. COVID-19 positivity rate closer to 10%
Vancouver data analyst believes B.C. COVID-19 positivity rate closer to 10% – Nov 16, 2020

“We should be separating those out, and I think there’s useful information there. Because if there are groups that are testing routinely in the general population, we could use that data to figure out the prevalence,” she said.

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“So, how many people in an area actually have COVID today. That would be really useful for all sorts of things — for capacity planning, for modelling, and just for understanding COVID and knowing how many of the cases we’re detecting via our normal testing route.”

Colijn said the positivity rate in B.C., even with those tests from the film industry, is concerning.

Read more: Coronavirus: Case count, positivity rate climbs in B.C.’s Southern Interior

“I think we should be acting to reduce transmission, and we should be doing it… well three weeks ago would have been a great time, maybe four. Maybe the second best time is two weeks ago, and the next best time is today.”

She said one way to break B.C.’s chains of transmission would be to make changes to the province’s testing strategy, by testing all close contacts of confirmed COVID-19 cases as soon as they’re identified.

Failing that, Colijn said there needs to be stronger restrictions on social interactions in the province.

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