Close to a third of Alberta’s active COVID-19 cases have no identified source

Close to a third of Alberta’s active COVID-19 cases have no identified source, sparking concerns that important data could be missing as the province eases restrictions and at the same time tracks a growing number of variant cases.

The percentage of active cases with no known source peaked at about 85 per cent in late November when Alberta’s contact tracing system broke down.

While it has improved dramatically since Alberta Health Services beefed up its contact tracing teams and caught up with the backlog, it currently sits at nearly 33 per cent — representing 1,856 of 5,706 active cases.

“We have a lot of contacts in our community that we cannot identify to the contact tracers,” said Craig Jenne, an associate professor at the University of Calgary in the department of microbiology, immunology and infectious diseases.

“So when we’re looking for who have you had contact with that may have had the virus, unfortunately the answer for … about a third of the viral cases is, ‘I don’t know.’

“And that’s always concerning, particularly given that Alberta up until [Monday] was really under quite a restrictive shutdown.”

Phased reopening

The province moved into Stage 1 of its phased reopening on Monday, allowing for some indoor dining at restaurants, one-on-one training in gyms and limited school and minor sports.

Jenne said easing restrictions will lead to more interactions in the community, providing even more opportunities for the virus to spread between people who don’t know each other.

“If we’re at a third already, as we increase our activity in the community one would only expect those anonymous or untraceable contacts to go up,” he said.

Craig Jenne, assistant professor of microbiology and immunology at the University of Calgary, says there are a lot of contacts in the community that can’t be identified — a concerning detail as the province eases restrictions. (Jennifer Lee/CBC)

According to Jenne, this hampers the ability of health officials to identify and contain outbreaks and use targeted measures to reduce the spread.

“If we see cases going up, if we see hospitalizations going up and we have to bring those back down, we do not have the precision data to say those cases are coming from this specific activity,” he said. “Instead, we will have to address this with broad strokes.”

Spread of variants

The spread of coronavirus variants — which are believed to be roughly 50 per cent more transmissible — could further aggravate the situation, according to Jenne.

“There is a greater likelihood that casual, anonymous contacts will lead to viral infection,” he said.

“No longer do you need those extended close contacts where you know the person. These could transmit through shorter interactions [such as] a lineup a store [or] on a bus … and we will see a greater number of cases coming from these casual unknown contacts.”

Alberta’s chief medical officer of health, Dr. Deena Hinshaw, said Wednesday the percentage of active cases with no known source involves some new cases in which the investigation is just starting.

But Hinshaw noted that others are complete and the source simply isn’t known.

“We know, with a long incubation period of 14 days, if people have been a part of various activities over that time frame, it can sometimes be difficult to identify where an exposure happened,” she said. 

Hinshaw said she continued to urge Albertans to download the province’s COVID-19 tracing app.

“We know that the more people who have this app, the more able we will be able to supplement the manual contact tracing with that automated, anonymous identification,” she said. 

Jenne said the ABTraceTogether app was suffering from an uptake issue.

“If only 10 per cent of the people are participating in this, then it is essentially useless,” he said.

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