The latest frontier of COVID-19 monitoring shows a persistent presence of the Omicron variant in the community, prompting Simcoe-Muskoka’s medical officer of health to warn residents not to let down their guard.
“When I look at the viral signal we appear to have a much lower amount of transmission of Omicron than in the peak of the wave in January but it’s still higher than it was before the Omicron wave began,” said Dr. Charles Gardner. “There’s still substantial risk and people need to take their precautions.”
As human testing becomes less commonplace in the community, there’s a heavier reliance upon wastewater testing results, which began in Simcoe County communities more than a year ago.
The general approach has been previously used to detect polio in some countries as well as the incidence of diabetes but was re-adapted during the pandemic to track COVID-19 infection.
Samples are now taken five times per week from the wastewater treatment facilities in Barrie, Collingwood, Midland and Orillia and are then sent to the Ontario Tech University in Durham for analysis to show how much virus is being shed locally.
Since the start of the month, those results are being compared against the number of COVID-19 hospitalizations at the local hospitals - Royal Victoria Regional Health Centre, Collingwood General and Marine Hospital, Georgian Bay General Hospital and Orillia Soldiers’ Memorial Hospital.
Graphs on the Simcoe Muskoka District Health Unit website often show the change in the wastewater results is almost shadowed a short time later by the change in the number of hospitalizations. Wastewater can give five- to 10-days’ warning before the changes are seen through hospitalizations.
The graphs show a plateauing of COVID-19 locally at what Gardner calls a significant level just as the province is lifting some restrictions. He expects that could lead to a rise in cases.
But the impact seems to be less severe, given a reduction in the number of hospitalizations.
He warns that the introduction of a new variant could change all that.
China, for instance, is experiencing a new virulent variant that has prompted the shutting down of some cities.
But Gardner points out that wastewater testing only reflects those on municipal systems and those spending time in the four Simcoe County communities, such as visitors or commuters and doesn’t result in precise numbers of infections.
Those with COVID-19 infection, whether they have symptoms or not, can shed SARS-CoV-2 virus RNA in their stool. Testing of the wastewater then provides patterns in the community allowing for the tracking of general transmission.
That information is then set against other data coming from percentages of positive cases coming from COVID-19 testing - which is now largely focused on high-risk settings - as well as reported cases, hospitalizations, intensive-care unit admissions, mortality and outbreaks.
Testing at Ontario Tech University includes a normalization process by cross-referencing the samples for Pepper Mild Mottle Virus, which is normally occurring in humans.
Gardner said that process helps in the understanding of the proportion of wastewater from human waste that is found compared to other sources caused through runoff or spring melt.
The information here is also set against similar information coming from neighbouring communities as well as from across the province, much like other data sources, and whether those are going up or if a new variant, or subvariant, is emerging and the impact lifting restrictions could have.
Samples from wastewater treatment plants, pumping stations and sewer-sheds in 101 municipalities across the province are being tested.
While wastewater testing produces no exact number of infections, it could provide a more complete picture because it captures all the people using that specific system, instead of reflecting just those volunteering to be tested, said Garner.
“We really need a composite of indicators, multiple sources of data” to show how prevalent the virus is and what the risk of people contracting COVID-19 is, said Gardner. “It contributes to our understanding. Although we’ve improved greatly, we still have quite a bit of transmission happening in the community.”
