Motorists wait to enter a Fraser Health COVID-19 testing facility, in Surrey, B.C., on Monday, November 9, 2020. THE CANADIAN PRESS/Darryl Dyck

Motorists wait to enter a Fraser Health COVID-19 testing facility, in Surrey, B.C., on Monday, November 9, 2020. THE CANADIAN PRESS/Darryl Dyck

COVID-19: What do rising positivity rates mean for B.C.? It’s not entirely clear

Coronavirus cases are on the rise but the province has not unveiled clear thresholds for further measures

If you’ve been watching the news, you’ve probably seen it: an exponential increase in COVID-19 cases, as well as a recent spike in deaths.

But a less-reported number is the positivity rate, which the B.C. Centre for Disease Control “has increased steadily and steeply” in recent weeks. In the week of Nov. 8-14, it rose to above six per cent according to a situation report released by the organization, hitting a level that is above anything seen during the first wave of COVID-19 this spring.

The maximum positivity rate during the first wave hit five per cent in April, but occurred when testing was much less widespread and targeted at high-risk individuals. The number of tests at the time was about nine times lower than it was during November, at only 7,500 tests compared to about 70,000 currently. For context, the positivity rate in the first half of October was under two per cent.

“That rate is the fraction of the number of positive tests that come back divided by the total number of tests,” said Daniel Coombs, a mathematics professor at the University of B.C. Positivity rates are typically more accurate when more people are being tested.

B.C.’s increasing positivity rate in recent weeks is doubly concerning because the number of weekly tests has stayed between 60,000 and 70,000 even as the positivity rate rose from 1.82 per cent to six per cent.

B.C.’s positivity rate has reached record highs in November 2020 as the province struggles with the second wave of the COVID-19 pandemic. (B.C. Centre for Disease Control)

“If you suddenly have more positive people and the number of tests stayed the same, then [the rate] would go up,” Coombs told Black Press Media by phone.

“You don’t want this number to test rapidly unless your testing policy is also changing rapidly, and that’s not the case, so having it go up is probably a bad sign. It’s indicating we are finding more.”

The positivity rate backs up what the daily case count and rising hospitalizations are saying: the number of people with COVID-19 in B.C. is on the rise, with health officials attributing much of the spread to private social gatherings and high-risk exercise classes. B.C hit a record 762 cases cases Wednesday (Nov. 18) and recorded its deadliest day of the pandemic on Tuesday with 11 deaths.

To put B.C.’s six per cent positivity rate into context, Coombs points to Stockholm in Sweden which has a positivity rate of about 20 per cent, or one in five people testing positive. Sweden, which has refused to bring in lockdowns, has an overall positivity rate of above 10 per cent.

Canada’s overall rate has about 6.6 per cent of tests coming back positive.

But what B.C.’s rising positivity rate means is hard to tell. B.C. imposed region-specific restrictions for the Lower Mainland on Nov. 7, which heavily limited gatherings of any size in public or private, and expanded those restrictions – and brought in a mask mandate – province-wide on Thursday (Nov. 19). However, the preliminary positivity rate reported on the B.C. CDC COVID dashboard for Thursday (Nov. 19), the last day public data was released prior to an expected drop this Monday afternoon, was even higher than it was prior at 6.7 per cent. The Fraser Health positivity rate reported Thursday is at 9.6 per cent, in line with the region having a disproportionally high number of new cases. But positivity rates are rising in other regions too, with Vancouver Coastal Health at 5.1 per cent and Northern Health at 5.3 per cent as of Thursday. Interior Health was at a 3.5 per cent positivity rate, while Island Health is at 1.4 per cent.

READ MORE: 6 things you need to know about B.C.’s latest COVID-19 health orders

READ MORE: Masks now mandatory in all public indoor and retail spaces in B.C.

B.C. has not publicly linked any particular positivity rate to levels of COVID-19 restrictions like other regions. In Ontario, positivity rates are tied into the COVID-19 response framework, the plan that sets out when certain restrictions will come into place. At above 2.5 per cent, Ontario would enter the most restrictive level of COVID-19 measures short of a full lockdown. In New York City, schools shut down last week because the city’s positivity rate reached its three per cent threshold. In May, the World Health Organization recommended that the rate remain below five per cent for at least two weeks before governments consider reopening.

Provincial health officer Dr. Bonnie Henry said that rate is being monitored, but not what higher rates could lead to.

“Per cent positive is something we watch,” said Henry. “It’s one of those metrics that if it’s above five per cent… that tells us there’s transmission in the community that is concerning. We’d like to see it lower.”

READ MORE: B.C. education minister wants to avoid school closures completely

READ MORE: B.C. records 516 more COVID-19 cases, 10 new deaths

READ MORE: More COVID-19 testing needed for senior home staff, B.C.’s advocate says


@katslepian

katya.slepian@bpdigital.ca

Like us on Facebook and follow us on Twitter.

Want to support local journalism during the pandemic? Make a donation here.

Coronavirus

Get local stories you won't find anywhere else right to your inbox.
Sign up here

Just Posted

Interior Health has declared the Cariboo Chilcotin a community cluster. (Angie Mindus photo)
Interior Health declares Cariboo Chilcotin region a COVID-19 cluster, 215 cases since Jan. 1

Most cases are related to transmission at social events and gatherings in Williams Lake

A vial of the Moderna COVID-19 vaccine is displayed on Jan. 5, in Salt Lake City, Utah. (Rick Bowmer/AP)
Power outage spoils COVID-19 vaccine at Tl’etinqox

Temperature-sensitive vaccine no longer viable after Jan. 18 event

Nuxalk elder Caroline Mack, 85, receives her first dose of the Moderna vaccine on Jan. 19, at the Nuxalk Hall. (Caitlin Thompson photo)
First vaccines roll out for Nuxalk elders, hospital staff and long-term care residents

The Moderna vaccine arrived in Bella Coola on Sunday, Jan. 17

Administering naloxone to a person experiencing a benzo-related overdose event won’t help. Naloxone is used to neutralize opioids. (Jenna Hauck/The Progress file photo)
Northern Health warning drug users of potential benzo contamination

The drug does not respond to naloxone, and is being included in street drugs

Maj.-Gen. Dany Fortin, vice-president of logistics and operations at the Public Health Agency of Canada, speaks at a news conference on the COVID-19 pandemic in Ottawa, on Friday, Jan. 15, 2021. THE CANADIAN PRESS/Justin Tang
B.C. records 500 new COVID-19 cases Wednesday, 14 deaths

Outbreak at Surrey Pretrial jail, two more in health care

Francina Mettes and Thomas Schouten with the 200-page document they submitted in December of 2018. (Travis Paterson/News Staff)
Dutch man, 94, facing unwanted trip home can stay in B.C. with wife of 45 years

Immigration offices cuts red tape so couple of 45 years can stay together in Victoria area

Health Minister Adrian Dix looks on as Dr. Bonnie Henry pauses for a moment as she gives her daily media briefing regarding Covid-19 for the province of British Columbia in Victoria, B.C, Monday, December 7, 2020. THE CANADIAN PRESS/Jonathan Hayward
B.C. Premier, health officials to discuss next steps in COVID immunization plan

Nearly 31,000 doses of vaccine the province expected by Jan. 29 could be curtailed due to production issues

Cannabis bought in British Columbia (Ashley Wadhwani/Black Press Media)
Is it time to start thinking about greener ways to package cannabis?

Packaging suppliers are still figuring eco-friendly and affordable packaging options that fit the mandates of Cannabis Regulations

Vancouver Canucks’ Travis Hamonic grabs Montreal Canadiens’ Josh Anderson by the face during first period NHL action in Vancouver, Wednesday, Jan. 20, 2021. THE CANADIAN PRESS/Jonathan Hayward
Horvat scores winner as Canucks dump Habs 6-5 in shootout thriller

Vancouver and Montreal clash again Thursday night

A woman writes a message on a memorial mural wall by street artist James “Smokey Devil” Hardy during a memorial to remember victims of illicit drug overdose deaths on International Overdose Awareness Day, in the Downtown Eastside of Vancouver, on Monday, August 31, 2020. THE CANADIAN PRESS/Darryl Dyck
B.C. paramedics respond to record-breaking number of overdose calls in 2020

On the front lines, COVID-19 has not only led to more calls, but increased the complexity

Eighteen-year-old Aidan Webber died in a marine accident in 2019. He was a Canadian Junior BMX champion from Nanaimo. (Submitted)
Inadequate safety training a factor in teen BMX star’s workplace death in 2019

Aidan Webber was crushed by a barge at a fish farm near Port Hardy

Southern resident killer whales in B.C. waters. Research shows the population’s females are more negatively influenced by vessel traffic than males. (Photo supplied by Ocean Wise Conservation Association)
Female orcas less likely to feed in presence of vessel traffic: study

Research the southern resident population raises concerns over reproduction capacity

Most Read