Ontario wastewater testing shows 'sustained increase' in COVID-19 rates

Public health officials tracking prevalence of COVID-19 through municipal wastewater testing say they're seeing a "sustained increase" in the viral signal in a variety of locations across Ontario, a sign that the number of cases are on the rise.

The bump comes after the province rolled back mask mandates and other restrictions including capacity limits for many indoor spaces, and was dwarfed by the Omicron wave earlier this year.

But observers say it's too early to know whether to sound the alarm, pointing to measures that are expected to protect Ontario's population, including a high rate of vaccination.

"We are seeing a sustained increase in the signal we are receiving," said Dr. Barry Pakes, the medical health officer for York Region, north of Toronto.

"That’s expected but still concerning," he said.

In the Greater Toronto Area, parts of Toronto, York Region, as well as the cities of Oakville, Milton and Pickering show increases in the viral signal, according to public health dashboards. The signal is determined by testing for signs of COVID-19 that is secreted by infected people.

The viral signal hasn’t changed much in much of Durham Region and Peel Region, the dashboards show. And in Burlington, the signal is going down. The rate of testing varies from once a week to a few times a week, and could be showing a delayed result.

But modelling by Ontario’s Science Advisory Table released last week suggests that the caseload is starting to increase provincewide, with estimates that the increased viral load detected in our water amounts to about 28,000 active cases, doubling in about six days.

"We are definitely in exponential growth. About 50 per cent of the public health units that are testing show exponential growth," said Dr. Peter Juni, the scientific director of Ontario's science table.

Juni pointed to eliminated restrictions on March 1, when the province removed a requirement to be vaccinated and removed capacity limits in most indoor settings.

“The task will be to take it a little bit slow. Keep masking if in doubt, and don’t increase your contacts too much,” Juni said.

Mask mandates were removed on Monday, but it’s likely that those changes haven’t yet been accounted for in the data, said Dr. Eric Arts, a Canada Research Chair in HIV Pathogenesis and Viral Control at Western University.

“I think March Break, coming up, is going to be a telltale sign of how much the wastewater signal will increase and I hope it doesn’t increase a lot, but I suspect that it will,” he said.

Dr. Vinita Dubey, Toronto’s Associate Medical Officer of Health, said the increase is expected after any reduction in restrictions, but it must be kept in perspective.

“As we remove some restrictions Omicron will spread. Now what we do know is that it is a less severe infection especially among those that are vaccinated,” she said.

The regions that are DNA testing their wastewater samples are seeing a new strain gaining ground.

“It is more than 50 per cent BA.2 which is an Omicron variant variant, which is not more dangerous per se, but significantly more transmissible,” Pakes said.