Wastewater testing for COVID-19 virus reaches its 'full potential' in N.W.T.

A toxicologist at the University of Saskatchewan is impressed with the N.W.T's wastewater testing program — and the public health response that followed detection of the virus in Yellowknife. 

"It's so exciting to see that a method like this is being used to inform the public health measures," said Markus Brinkmann, an assistant professor with the School of Environment and Sustainability. "That's perfect and that, I think, is realizing the full potential of the method."

In a news release Wednesday, the territory's chief public health officer alerted the public that wastewater monitoring had detected the virus that causes COVID-19. Dr. Kami Kandola has asked everyone who recently travelled to get tested. 

The city's last known case of COVID-19 was announced on Nov. 24. Kandola said that case was also picked up in wastewater, but she expected the signal to subsequently go down. It went up instead. 

Saskatoon's experience

Brinkmann has been testing wastewater in Saskatoon since July. His tests predicted a surge in cases in late November.

"And that is exactly what happened," he said.

The method is adept at detecting spread in people who don't experience symptoms and may never learn they have it.

"Those persons are usually one of the great risks of virus spreads," Brinkmann said.  

Wastewater testing detects genetic signals from SARS COVID-2, the virus that causes COVID-19, and the tests are highly sensitive. But the method cannot typically track the number of cases present in any given population. 

In Saskatoon, researchers have had more time to gather wastewater data, and measure it against subsequent case numbers. That's allowed them to calibrate the models that make predictions. Without that, Brinkmann, said, it's "really hard to make quantitative predictions."

Public's response as important as testing

Brinkmann said the public's response to information from wastewater testing is just as important as the testing itself. 

When his group puts out information to warn the public, "we did actually see the community responding." 

He says he got about 20 emails from families making changes, such as pulling their kids out of hockey practice. 

"One of the biggest advantages is that the community gets a feel for what is happening and they can respond to it. Oftentimes COVID-19 is one of those risks that is really hard to comprehend, especially if case numbers are low. The raw data can provide another source of information there."

Brinkmann says the only other way to find case numbers is to do testing of asymptomatic people, which is what's happening now with people who were in self-isolation. 

"I really think the [territorial] response to this new information is spot on."

'Learn as much as we can as we go along'

Dr. Steve Hrudey is a retired toxicologist with the Faculty of Medicine and Dentistry at the University of Alberta. He chairs a national research advisory panel for the Canadian Water Network, which has been advising a number of groups across Canada who are testing wastewater. 

He says wastewater testing for SARS COV-2 first started in the Netherlands, but is now being deployed in roughly 50 countries. A group at the University of Alberta is monitoring 12 wastewater treatment plants in that province. Another group at the University of Calgary is sampling in that city. 

"Everybody is doing the best to learn as much as we can as we go along," Hrudey said. "But I don't think there's anybody that has absolute answers."

Wastewater testing FAQ

Can there be false positives? 

Kind of, Dr. Kandola said Wednesday. The tests look for genetic signals of SARS-CoV-2, the virus that causes COVID-19. Someone could have tested positive, recovered, and still be shedding dead virus for weeks. There's no way to detect whether the virus detected is dead or viable.

"We can call it a false positive if it's a dead virus and no risk of transmission," Kandola said, "but we don't know. So this is a precautionary approach." 

Can the test really pick up just one case? 

Yes. Traces of the virus were detected after an essential worker in Yellowknife tested positive on Nov. 24. Kandola said she then expected the signal to decrease as that person recovered. Instead, the signal increased slightly, but stayed steady over at least two days, suggesting it did not spread further. 

How reliable are the methods overall? 

According to Brinkmann, very. An interlab comparison study organized by the Canadian Water Network found most results from different researchers were in line with each other. However, there has yet to be a standardized approach. 

Has the virus been detected in other N.W.T. communities? 

Yes. Wastewater samples in Fort Smith detected the virus presumed to be related to the cases who were in self-isolation. The signal has since diminished. 

Why is there a delay in results? 

N.W.T. wastewater samples are being sent to the National Microbiology Lab in Winnipeg for testing. The delay is due to travel times. 

When will we get the next results?

The results from samples taken Dec. 4 reached Kandola Dec. 9. The next results will cover the time period from 2 p.m. on Dec. 4 to 2 p.m. on Dec. 7. They're expected to arrive at the end of this week or early next week.

"It all depends on transport delays," Kandola said.