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Why not use wastewater to better monitor the evolution of COVID-19? | Coronavirus


Across the country, authorities are no longer able to screen all people infected with COVID-19. But researchers who analyze the concentration of the virus in wastewater do not understand why their data is not used more to follow the evolution of this wave, especially when the testing centers have reached their maximum capacity.

We know that sewage can detect the level of concentration of the virus in a community. And the advantage of this indicator is that it is not related to clinical tests. As we have exceeded the capacity of testing centers and testing strategies change, the signal from wastewater does not changesays Robert Delatolla, associate professor in the Department of Civil Engineering at the University of Ottawa, who has been analyzing the city of Ottawa’s wastewater since the start of the pandemic.

Knowing that the reported cases are largely underestimated, the authorities are now relying on the positivity rate and the number of hospitalizations to monitor the progression of transmission. But as with all indicators, they have limits, recalls Mr. Delatolla.

For example, if screening is limited to a segment of the population, the positivity rate becomes less reliable. As for hospitalizations, there is a delay of about two weeks before the increase or decrease in cases is reflected in their number. It is therefore more difficult and longer to see if the measurements are working.

Sarah Dorner, professor in the Department of Civil, Geological and Mining Engineering at Polytechnique Montréal, adds that platforms for self-declaration of infections, such as what is proposed by the Government of Quebec, will not be sufficient. Not everyone will do it, says Professor Dorner, who has been working for six months with a group of Quebec researchers who analyze the province’s wastewater.

This is why, for Mr. Delatolla, the analysis of the wastewater would offer a very good overview of the number of cases to come and allow to see when it will start to stabilize and decrease. I think it’s a very valuable tool right now. These analyzes could help the authorities to better determine the moment to relax or tighten certain health rules, he believes.

A proven technique

Robert Delatolla.

Professor Robert Delatolla poses in front of a pumping station used to collect samples of wastewater that is screened for COVID-19.

Photo: The Canadian Press / Adrian Wyld

While this type of indicator does not quantify an exact number of cases in a region, it does allow us to see a change in trends, even before we can see the number of cases increasing, explain Ms. Dorner and Mr. Delatolla.

Once it is in the sewage, it is well known that the virus is spreading in the community.

A quote from Sarah Dorner, Polytechnique Montreal

When these two researchers compare the curve of the concentrations of the virus in wastewater to that of the reported number of cases, the correlation is striking. The two curves are almost identical, except that the wastewater curve is several days ahead.

Wastewater also makes it possible to detect the arrival of new variants or new waves.

Mr. Delatolla adds that their analyzes detected the Omicron variant as early as the end of November and that they observed the concentrations of Omicron increase around December 10. In Quebec, analyzes of wastewater showed that the Omicron variant was indeed present as of December 4. The Quebec government only confirmed the presence of the Omicron variant on December 17.

Sarah Dorner says wastewater testing is all the more important when the screening system is no longer delivering.

During the third wave, she explains, Montreal has been very successful in screening and identifying cases and tracing contacts. People received their results within hours, so the wastewater analysis was not necessarily faster. But at the moment, the results are coming several days later and we are only testing a portion of the population; wastewater results would be much faster and more efficient in seeing the evolution of community spread.

Wastewater is like the second engine of an airplane. When the first engine – scouting – fails, sewage becomes a very useful tool. When the follow-up of clinical cases is rapid, we are not very competitive, but when we are in the current situation, there is no competition.

A quote from Sarah Dorner, Polytechnique Montreal

An additional tool to guide the authorities

Providing this data to the public, Dorner said, would give people a better understanding of the scale of the situation.

We say we want to empower people. But they were not provided with all the essential elements to assess their level of personal risk. People have no idea what is going on around them. Wastewater can help us understand the level of risk in a community.

In Quebec, the research project has no more funding since December. Previously, samples were taken daily from across the province. However, the Government of Quebec has never used these data.

On the Ontario side, sampling continues. In fact, of the approximately 250 wastewater collection sites across the country, 175 are in Ontario. Sampling sites are found to a lesser extent in Alberta, British Columbia, Nova Scotia, Manitoba and the Northwest Territories.

Some local public health departments use this data more than others, according to Delatolla. Ottawa is probably one of the cities that regularly uses wastewater analysis to monitor the epidemiological situation and even to make decisions about what to do next. The results and graphics are easily accessible to the public.Have (New window)Have

In fact, in December 2020, it was these scans that guided Ottawa’s director of public health, Dr. Vera Etches, to impose tougher measures even before the number of cases increased in her community. The number of reported cases was still stable, but the sewage showed an increase in the concentration of SARS-CoV-2, explains Mr. Delatolla. The cases did increase shortly thereafter.

Dorner adds that this type of analysis can be used to monitor the situation in vulnerable settings, such as long-term care homes, hospitals and detention centers. Samples can be taken at the exit of these establishments. And as soon as we see a positive, it is a sign that we must go for screening and increase the vaccination, says Ms. Dorner.

According to Delatolla, the Ontario government will soon add wastewater analysis to its dashboard and make the data available to the public. People will be able to follow the wastewater curve, as they did with the number of cases, he said.

For her part, Ms. Dorner would like the project in Quebec to obtain more funding, especially to establish a long-term monitoring system.

Establish a monitoring system

The two researchers believe that analysis of wastewater must be a method used not only during this important wave, but also for the rest of the pandemic.

We won’t be able to continue testing so many people over and over again. The cost would be far too high. But you can trace thousands of people with a sample. And we could do it sporadically, says Mr. Delatolla.

These researchers add that the wastewater watch can be used not only to monitor SARS-CoV-2, but also to monitor other viruses, such as influenza or respiratory syncytial virus (RSV). In addition, for several years, Canada has analyzed wastewater to monitor the consumption of illicit drugs or to detect the presence of contaminants.

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