With limited access to polymerase chain reaction (PCR) testing in provinces across the country, obtaining an accurate clinical picture of the prevalence of COVID-19 has become increasingly difficult in recent months.
However, this paved the way for wastewater testing to play an increasingly critical role in monitoring the transmission of COVID-19 to communities, according to Mark Servos, Canadian research department for water quality research and a professor at the University of Waterloo in Ontario. .
“Wastewater is completely independent of whether you are tested or not – everyone is sorry,” he told CTVNews.ca in a telephone interview Monday. “Wastewater is indeed one of our only reliable tools to determine what is happening in terms of distribution in the community.
Although recently in the spotlight, the Canadian Public Health Agency (PHAC) has been monitoring wastewater samples for SARS-CoV-2 since the fall of 2020. The process involves measuring the concentration of COVID-19 genetic material in wastewater to understand what is common in the community, explained Elizabeth Edwards, a professor in the Department of Chemical Engineering and Applied Chemistry at the University of Toronto. Edwards is also part of a research team testing COVID-19 levels in wastewater collected from the Greater Toronto (GTA) area.
Studies have shown that traces of SARS-CoV-2 ribonucleic acid (RNA) can be found in the faeces of patients with COVID-19, which means that they may be able to excrete the virus in waste. From the toilet, their waste enters the sewer system and is transported to the municipal wastewater treatment plant. A sample of wastewater is then collected from the plant and transported to one of several laboratories across the country for processing. Samples are usually collected three times a week.
In the laboratory, the sample is placed in a centrifuge so that its solid components can be separated from its liquid components while being filtered, Edwards said. This allows researchers to extract RNA from the sample and prepare it for PCR testing.
The PCR test is identical to those performed in COVID-19 nasal swab clinics, she said. He detected genetic material from the SARS-CoV-2 virus and amplified it for analysis.
“We can then link the number of copies of this piece of RNA back to the volume of water we started with,” Edwards told CTVNews.ca in a telephone interview Tuesday. “If we know we have 100 in those 500 [millilitres]we can achieve concentration. ”
While PCR tests are also performed on wastewater samples, these tests target a different part of the virus, namely the N or E genes. In particular, the N-gene appears to remain well-preserved in wastewater, Servos said.
Once the data is collected, the results are reported regularly to the public health units. The methodologies may vary slightly from province to province, but the goal is to find available levels of COVID-19, Servos said.
COVID-19 WASTEWATER SIGNS INCREASE
One of the reasons why wastewater testing has become so important for understanding the extent of COVID-19 in the community is the high transmittance associated with the Omicron variant, Servos said.
“Before Omicron came along, we had a very good relationship between our wastewater samples … and the number of clinical cases,” Servos said. “When Omicron showed up and hit everything, clinical trials were kept to a minimum, just an emergency [cases] and the relationship began to fall apart. “
The Ontario Wastewater Monitoring Network consists of 14 laboratories working to detect COVID-19 levels in wastewater samples from 174 sites in about 70 cities or health regions, according to PHAC. The results of the wastewater analysis cover about 75 percent of the total population of the province.
Servos is based in Waterloo, Ont. a region that includes the cities of Waterloo, Kitchener and Cambridge. The samples processed in his laboratory at the University of Waterloo cover about 82 percent of the region’s population, Servos said. As of April 2, the average weekly value for the city of Waterloo for the number of N-gene copies per milliliter is about 415, which is a steady increase in COVID-19 levels since mid-March. A major driver of this growth is the rapid spread of the Omicron BA.2 sub-variant within the province, Servos said.
“We have now seen that BA.2 is almost 100 percent in most wastewater [samples] which we are studying, ‘said Servos.
With the recent wave of Omicron that hit Canada and peaked in early January, COVID-19 wastewater levels have risen dramatically in Ontario, Servos said. After concentrations fell in February, the province is again seeing an increase in wastewater signals, he said.
“A lot of people are getting COVID at the moment and the wastewater signal is completely in line with that,” he said. “It’s growing in all regions and we’re seeing more and more people getting COVID.
Wastewater data collected from the Ontario COVID-19 Scientific Advisory Table taken on April 14, 2022.
The last four weeks in Ontario have seen a steady increase in COVID-19 wastewater signals, which will continue to rise, Servos said. Concentrations in the province are already well above what was studied in the Delta and Alpha waves, he said.
“The next week or two will be very critical in trying to figure out what will happen in this wave of pandemics,” Servos said.
As part of the Alberta Wastewater Surveillance Initiative, researchers from the University of Alberta and the University of Calgary have teamed up to collect and test wastewater samples across the province. Both universities work with Alberta Precision Laboratories to process samples from 20 sites in 42 cities and communities, accounting for 79 percent of the province’s population.
Casey Hubert, a researcher in geomicrobiology at the University of Calgary, is one of those researchers.
In Calgary, Alta, where Hubert lives, he noted a steady rise in COVID-19 levels in wastewater collected in the past month or more. Each data point collected and plotted was higher than the previous one, he said. While the latest data point shows a slight decrease in the number of copies of SARS-CoV-2 detected per day, Hubert said he expects concentration levels as a whole to continue to rise.
“Unfortunately, I expect the data to continue to rise,” Hubert told CTVNews.ca in a telephone interview on Wednesday.
In British Columbia, wastewater samples are collected from five different Vancouver Metro sites and processed by the British Columbia Disease Control Center, in collaboration with the University of British Columbia. The samples cover about 49 percent of the province’s total population, said Natalie Pristaeki, a microbiologist at the Public Health Laboratory at the BC Centers for Disease Control.
Looking at data from Ontario’s sewage analysis, which Priestayki said is often ahead of British Columbia in terms of waves of infection, she is slightly concerned.
Data from her own province show a steady increase in COVID-19 concentration levels in wastewater samples as well. But those levels are not close to where they were on top of the Omicron wave earlier this year, she said.
“There is nothing to worry about at the moment,” Pristaeki told CTVNews.ca in a telephone interview Wednesday. “We are very far even halfway to Mount Omicron.”
DATA VARIABILITY MAY CAUSE “ERROR”
One of the benefits of wastewater testing is how cost-effective it can be, Hubert said, especially compared to individual PCR testing. Although it may be more expensive than clinical trials, it could be a fairly quick way to test COVID-19 levels in a large group of people, he said.
“It’s a very effective tool when you can take a sample to cover a large part of the population,” Hubert said. “In a city like Edmonton or Calgary, if you can do a single PCR test and get a signal from a million people, that’s a really powerful way to assess the trajectory of a pandemic.
It also does not depend on voluntary participation in the same way as PCR testing, Servos said.
“It doesn’t matter if you can’t be tested, or you’re vulnerable, or you’re asymptomatic,” he said. “Wastewater captures this, so it’s an integrated signal that’s independent of clinical testing.”
However, there are some challenges with wastewater testing, mainly due to the variability of the data from each sample, Edwards said.
Wastewater treatment plants differ in age and design, she explained, which could lead to more dilution of samples in some places than in others.
“There’s a big margin of error, 50 percent easy,” Edwards said. “But what else to do?” We need to look at the data we have, no matter how noisy and uncertain, and make our best predictions. “
Several other factors could also affect COVID-19 signals in wastewater, Hubert said. In Calgary, for example, rainwater is stored separately from sewage collected in the sewer system, he said. In other cities, both are combined, which would dilute the covid-19 signal in these samples. Different communities also have different proportions of domestic and industrial water use, which contributes to their municipal wastewater.
Hubert said he acknowledged that while it was tempting to compare levels between different cities or health regions, those comparisons would not necessarily be accurate.
“Every wastewater system for every community will have a lot of variables in it,” he said. “We just keep these variables …
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