At a time when certain provinces are limiting access to screening tests for COVID-19 by the PCR method, even as the demand for a diagnosis explodes, several experts deplore the fact that the daily reports no longer reflect the true portrait the spread of the virus in communities.
But what is released into our wastewater may well help us to better assess the prevalence rate of the disease, it is believed.
Researchers from coast to coast have set out to monitor the content of sewage since the start of the pandemic, observing the presence of tiny traces of the virus in order to track its progress.
According to scientists involved in this labor-intensive process, the method does not offer a perfect measure of the level of circulation of COVID-19, but it can help identify areas with the greatest contagion.
And in the event that the screening capacity is exceeded and cases are no longer systematically reported, wastewater monitoring can prove very useful to health authorities, the researchers say.
“Currently, we have this problem where we have reached the limit of our capacity to perform screening tests,” observes researcher Mark Servos of the University of Waterloo. But sewage doesn’t care whether there are clinical tests or whether people are asymptomatic. ”
“Everyone who defecates in the pipe will be included in our analyzes,” he summarizes.
By limiting access to PCR testing in an effort to save resources, provinces will necessarily create an imbalance between the number of reported cases and the actual number of infections. Especially with the presence of the Omicron variant which is transmitted even more easily.
According to Dr Christopher Mody, an infectious disease specialist at the University of Calgary, PCR test diagnoses are believed to be barely one-sixth or one-eighth of the actual number of cases. This gap may continue to grow with people relying on rapid tests and those who simply don’t get tested.
“We have to know what the real number is,” he insists, stressing that the analysis of wastewater could help to partially compensate for the lack of data.
“I would say that wastewater is an extremely useful tool in assessing the magnitude of the disease burden,” says Dr.r Mody.
By observing weekly trends in the presence of the virus in wastewater, one could not only measure the extent of transmission, but also identify the type of variant that dominates.
Data collected in Saskatoon showed an 87.7% increase in viral load in the city’s wastewater last week, including an 808.2% explosion in the amount of traces of the Omicron variant.
The process of monitoring wastewater involves collecting samples from the basins of water treatment plants, then isolating and measuring traces of COVID-19 particles.
Mark Servos calls the procedure “complex” and “tedious”, but results can be achieved in a matter of hours.
Samples are collected daily in some cities, including Ottawa, which launched its program in April 2020. Elsewhere, it is preferred to take samples a few times a week.
“We see the concentration increase in our wastewater,” confirms Robert Delatolla, a civil engineer from the University of Ottawa who follows the evolution of the data.
No money in Quebec
If the method seems to be of interest to several provinces that want to improve surveillance of the presence of the virus in wastewater, Quebec is taking the opposite direction.
A professor at Polytechnique Montréal, Sarah Dorner reveals that a six-month pilot project, funded by the Quebec Research Fund, the Molson Foundation and the Trottier Family Foundation, ended in early December.
“We had no more funding to continue,” she wrote in an email adding that her team had observed “a rapid increase in SARS-CoV-2” in Montreal’s wastewater just before the project was launched. stopped.
This practice of monitoring wastewater did not originate with COVID-19. She had served around the world in the past to monitor for the presence of polio.
Limits
Although the researchers involved see it as a useful additional tool, the analysis of wastewater can only see what is happening in a specific and small community.
In addition, the virus concentrations in the rejects do not allow the severity of the cases to be determined.
Environmental factors, such as the snow which melts and dilutes the water in the ponds, can also affect the results of the analyzes. In addition, researchers have a limited ability to perform tests on a regular basis.
Despite everything, the Dr Christopher Mody believes this type of surveillance can signal public health authorities that an outbreak is imminent when concentrations rise rapidly in a specific location.