Analyzing the content of our sewers is becoming an increasingly important tool as Canadians adapt to living with COVID-19, says a group of researchers pushing for a national wastewater surveillance system.
Currently, samplers are set up in about 250 sites across the country. Many of them in Ontario and Alberta, where wastewater from 70 per cent of the population is analyzed. The results are publicly available.
"We are actually able to gain a lot of information from that one sample," says Rob Delatolla, a civil engineering professor from the University of Ottawa. "We are able to understand how much total virus there is in that sample, and really to measure disease severity in the population base."
PCR test data, though never fully accurate, provided a portrait of the prevalence of COVID for much of the pandemic. However, during the Omicron wave, testing sites were overwhelmed and positive test numbers provided less information to keep track of infections.
Many experts say mass PCR testing is likely to wane with time, and wastewater may be able to fill in some of the blanks.
It has limitations, though. It measures the viral load in a community, the disease severity, but does not clearly break down how many people are infected. It can also be tricky, for instance, when dealing with environmental factors like melting snow.
In Quebec, a six-month pilot project to boost water surveillance funded by the Fonds de recherche du Quebec and the Molson and Trottier foundations ended in early December.
Doug Manuel, the director of the Coronavirus Variants Rapid Response Network (CoVaRR-Net) wastewater surveillance group, says this type of monitoring won't replace other tracking methods, but it can be a valuable tool.
"Everyone poos," he says. "We call it a passive surveillance system. You don't actively have to go and get tested. The virus is shed and we just measure that as it comes down in wastewater treatment plants."
CoVaRR-Net cites examples of wastewater's use in uncovering COVID-19 before cases were identified, including infections in the Northwest Territories, in several First Nations communities, in long-term care facilities in Hamilton, Ont. and Toronto, and on university campuses in Windsor, Ottawa and Guelph, Ont. It also showed early detection of waves in cities like Kingston, Ont. and Edmonton.
Used properly, the information could provide an early warning signal for the most vulnerable as the approach to health measures evolves.
Amy Hsu, a scientist at the Bruyere Research Institute in Ottawa and data platform director for CoVaRR-Net, says outbreaks in long-term care facilities tend to originate from staff exposed to the virus in the community. By monitoring wastewater in neighbourhoods where workers live, facilities may be able to anticipate threats and implement measures to protect residents.
"Rather than always subjecting staff to testing twice a week, and all visitors to testing, we can actually monitor the risk in our community," says Hsu, and then act on the information available.
McGill University's genome centre is also providing key information. The centre has focused on next-generation genomic studies for years, and in the face of COVID-19, served to sequence clinical samples. However, it is also analyzing samples of wastewater in its most powerful sequencer.
The technology allows researchers to identify emerging and new variants early on, but also to locate the geographical areas where they are found.
The head of genome sciences Jiannis Ragoussis says the method provides "huge" value for money. "We get rich data with 10 times less effort than standard surveillance clinical collection-based systems."
Wastewater surveillance was used to track cases of polio 25 years ago. But the pandemic has forced scientists to move the technology forward.
"Big scientific advances often come from a threat to humanity," says Manuel.
"Can you imagine the return on investment if we had what I call the 'WWWW,' the World Wide Wastewater Web? Can you imagine our ability to identify variants and what would have happened if we had that already?"
But researchers also say wastewater surveillance could also be used for other viruses and bacteria.
"The applications are massive," says Delatolla. "It's not just for disease targets; it is for instance drugs too. You can look for opioids, for illicit drugs, you can understand what is happening on a community level."
All that from the sewer.
