Growing proportion of Alberta COVID-19 cases have no known source

While Alberta's daily COVID-19 case counts remain low compared with the peak of the third wave, a growing proportion of cases have no known source — a trend experts say is likely related to the province's reopening.

According to provincial data, contact tracing had been unable to pinpoint a source of transmission for 39 per cent of active cases (246 of 624 active cases) and 40 per cent of those identified in the past week (125 of 312 cases between July 5 and July 11).

Those numbers were hovering in the low 30s in early June

Experts say the increase is to be expected now that Alberta has lifted virtually all of its restrictions.

"What can happen as we reopen is people just have so many more contacts," said Carolyn Colijn, a math professor and infectious disease modeller at Simon Fraser University

"Now that things are completely reopen and people visit different venues, different workplaces, different social gatherings, of course that's a huge load on trying to identify and call people that might have been exposed," Colijn said.

More anonymous contacts

Craig Jenne, associate professor in the department of microbiology, immunology and infectious diseases at the University of Calgary, noted the number of cases with an unknown source is down dramatically from second wave late last year when Alberta's contact tracing system broke down.

In November, the number of active cases with no identified source peaked at about 85 per cent.

"Right now, the number of cases is small, which means our contact tracers can be fully engaged," he said.

"But the fact that still four out of 10 cases is untraceable really speaks to the method of transmission in the community, and that is a lot more anonymous contacts, which is to be expected."

Alberta Health said contact tracing continues "around the clock," and throughout the pandemic at least 30 per cent of cases have not been resolved.

"While there has been a small increase reflected in the online data of 'unknown exposures' recently, there is no indication this is a long-term trend at this time," a spokesperson said in a statement emailed to CBC News.

The data includes cases where a public health investigation is still underway and the source of exposure could still be identified, it also cautioned.

"While health officials work hard to identify the source of exposure, this work is extremely complex and is not always possible, particularly if an individual visited multiple locations," the statement read.

"The best way to protect yourself and those around you is to get fully vaccinated with two doses."

Meanwhile, Jenne said he believes improving uptake for a contact tracing app that can identify and alert anonymous contacts is the key moving forward.

"Until we embrace those, we are going to continue to see outbreaks. We will continue to see potential restrictions in the future in certain communities or activities."

Given the resumption of inter-provincial travel, Jenne said the federal app — which the Alberta government never adopted, opting to promote its own Alberta app instead — would be the best bet.

"We really need everybody to be on the same page as borders reopen, as people are moving freely across provinces," he said. "We want one app that tracks your risk of exposure wherever you are in the country."

Increase in cases expected

Dr. Alex Wong, an infectious disease physician based in Regina, expects cases will start to rise, driven by the more infectious delta variant, with regions experiencing the lowest vaccine uptake being hardest hit.

In principle, he said, increased use of the federal app might help but he believes most people in Alberta and Saskatchewan have already made up their minds.

"We just kind of have to accept the fact that there is going to be a degree of community spread and our public health people will manage those outbreaks as best as possible."