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How a Newmarket biostatistician is using Rt to track the impact of reopening

Ryan Imgrund is noting an alarming increase in the number representing the rate of COVID-19 transmission since restrictions have been loosened
2020 24 Ryan Imgrund
Newmarket biostatistician Ryan Imgrund is tracking Rt values in the region and province. Supplied photo

Newmarket biostatistician Ryan Imgrund began measuring the pace of the coronavirus pandemic locally and across the province before many public health officials truly knew what we were up against.

He began posting his COVID-19 modelling data on Twitter in mid-March based on the limited data then being provided by Public Health Ontario, he said, and he has become an acknowledged regional expert since then.

“My goal at the time was to estimate how bad things would get in Ontario,” said Imgrund, who is also head of the science department at Newmarket’s Sacred Heart Catholic High School. 

His “basic graphs” soon began attracting attention, which continued to grow as the pandemic escalated around the globe.

Shortly after that, Southlake Regional Health Centre asked him to model local COVID-19 numbers as their biostatistician, he said.

Last March, his graphs forecast that Ontario's cases would peak around 30,000 cases, which turned out to be an accurate prediction, with Ontario reporting just over 34,000 cases today as it continues its downward trend in new cases.

However, he said the “fast burnout rate” matching the rapid acceleration of cases isn’t occurring as he had anticipated.

“That’s one of the reasons I actually started calculating the Rt value,” he said. “The model I had at the very very start (of the pandemic) got us to where we’re at now, but it’s not tapering off as fast as it came in.” 

Rt, or the reproduction number, measures the burnout rate of the virus, Imgrund explained.

It’s a number that has grown in importance as Ontario moves into reopening stages — and Imgrund said he is noting "an alarming trend" of rising Rt values in regions that have reopened.

Rt estimates how many infections can be attributed to one person with COVID-19, he said.

“If you have an Rt value of 1, it means one person with COVID-19 is infecting one other person. Now, obviously, with an Rt of one, one person always infects one person, and that person always infects one person, and that person always infects one person, we’re going to have COVID-19 around forever,” Imgrund said.

“So the ultimate goal is to drive Rts to a value under one.”

When outbreaks in long-term care and group homes were skyrocketing York Region’s COVID-19 cases in mid-April, the institutional Rt value was 2.5 — meaning every infected person was causing 2.5 more cases.

The last time York Region’s Rt value was above 1 was June 6, according to Imgrund’s data. 

On his June 24 chart, five days into stage 2 reopening, York Region has a “yellow light” Rt value of .90, compared to a “green light” for Halton at .81 and Durham at .63.

Twelve days into stage 2 reopening, neighbouring Simcoe-Muskoka has a “red light” Rt value of 1.58 — the highest among the regions Imgrund is currently tracking.

Moving into stage 2 reopening today, Toronto is at .66, while Peel Region is at 1.20. 

In European countries, the Rt value is used exclusively to determine if regions are able to open, Imgrund said.

“When Ontario’s chief medical officer of health spoke about reopening, the first metric he mentioned was the Rt value, but that being said, the first round of reopenings didn’t seem to link a lot with the Rt values,” Imgrund concluded.

In fact, he suggests some regions with lower Rt values, including Peel and Toronto, hadn’t initially moved to reopening likely because they still had a high number of active COVID-19 cases.

“Toronto’s Rt value was low, but they had so many cases per capita, so many infections out there, the general population’s susceptibility would still be high,” Imgrund said.

At the time of the first stage 2 reopening on June 12, Simcoe-Muskoka had a higher Rt value than York Region, but only four weekly cases per 100,000 people, whereas York Region was at 20 weekly cases per 100,000 and didn't get the thumbs up for reopening.

If weekly new cases drop under five, the province appeared to be automatically moving those regions to reopening, Imgrund concluded. And regions with values higher than 15 weekly cases didn't advance to a reopening stage.

For instance, Haldimand-Norfolk had 14 cases per 100,000 and advanced to stage 2, while Peel did not with 18 cases per 100,000.

When York Region moved to stage 2 reopening June 19, it had nine weekly cases per 100,000, and is now at eight weekly cases. 

Simcoe-Muskoka has jumped to eight weekly cases per 100,000 from four since its stage 2 reopening nearly two weeks ago.

“That’s a very important metric that they seem to be using,” Imgrund said. “But I think the Rt will become useful in monitoring how successful regions are with their reopenings.”

In fact, Imgrund has tracked Rt values above 1 following reopenings in several regions, including Simcoe-Muskoka, where the rate has increased 133 per cent (rolling average in the last 14 days) to 1.58, and Wellington Dufferin Guelph, where the rate has increased 125 per cent to an Rt value of 1.49.

“Some increase is to be expected,” he said. “But in other countries, like Germany, when they reopened, their Rt never jumped up to 1. It would jump up to 0.8, it would jump up to 0.9, but very rarely would communities reopen and then have the Rt jump up to 1 or higher.”

He warned that the health care system will quickly become overwhelmed if Rt values above 1 continue for a longer period of time.

“The issue with the value of 1 is that we will see new COVID cases, it’s not going to get better, it’s going to get worse.”

With Ontario public health officials anticipating a second wave of COVID-19 this fall, Imgrund said he is following the situation in South America with growing trepidation, where cases are growing significantly again.

“One of the reasons this worries me is that they have a season reversal to the Northern Hemisphere, so if I fast forward six months, we’re looking at November, December, and are we going to see that really really big second wave that South America seems to be seeing now?”

Watching the trends so clearly outlined by his modelling makes Imgrund a strong advocate for mandatory face coverings in public places, including retail outlets, public transit and workplaces, with appropriate medical exemptions.

“In my opinion, if we just continue to do what we’re doing right now and we continue to reopen, I don’t think we can expect that our values will stay under 1,” he warned.

“If Rt isn’t falling under 1 by us doing what we’re doing now, reopening is certainly not going to drive it under 1. We have to change things,” he emphasized.

He said he hasn’t left his home in Georgina without a face mask since the beginning of April.

While testing has increased significantly in Ontario, the continued “random testing” is only revealing the tip of the iceberg of the province’s number of COVID-19 cases, he believes.

Testing shows only two to four per cent of Ontarians have been infected with COVID-19, Imgrund said.

“They’re not very high values right now because it's asymptomatic testing — if we run something like 5,000 asymptomatic tests, we may only find two to three cases.

“We’re testing more, but we’re only testing asymptomatic people who want to be tested,” he said. 

Unfortunately, until the beginning of May, the province had ruled out testing of many individuals who had symptoms, even those who had travelled to COVID-19 hotspots, he said.

“Up until then, they did not assume community transmission, even though this was happening for sure in March, maybe as far back as February, but 100 per cent in early March we had community transmission COVID-19,” Imgrund asserted.

What’s required to get a truer picture of the virus is focused testing on target groups.

“If you have the capacity to do 25,000 tests per day, like Ontario seems to be able to do, they need to be tests targeted at populations who we think may actually be carrying COVID,” he said. “To randomly test 1,000 people who just want to be tested for fun, you may only find one person.” 

In York Region, where testing has increased significantly to close to 9,000 specimens weekly, the positivity rate is one per cent, while the province's rate increased to 1.8 per cent as of June 22. 

It’s likely many of the individuals being tested now want to find out if they had a prior infection, which isn’t indicated by these tests, he said.

“I’ll be honest, I’m really looking forward to when serological testing is available here in Ontario to see how many underlying infections we actually have.”

Based on data from the U.S. and Europe, it’s reasonable to estimate that for every one reported COVID-19 case, 15 are unreported, he said.

Many Ontario epidemiologists are estimating between 300,000 to 600,000 people have been infected with COVID-19, he added.

If you ask Imgrund why COVID-19 has so easily passed from one person to another, he’ll tell you it’s because many public health officials had experience working with SARS. 

“It took a very long time, I think, for a lot of individuals to acknowledge that, one, it was as bad as it was, and two, to acknowledge that even though it is in the SARS family of viruses, it does not act the same way as SARS does,” Imgrund said.

With SARS, there was a one-day period between exposure and fever, unlike the two to 14-day incubation period with COVID-19.

“It was actually very very easy to detect if somebody actually had SARS, and actually easy to contain that way,” Imgrund said.

“If we’re looking at COVID, there are some people that spend up to two weeks in a state when they are actually presymptomatic and they are actually able to spread the virus in those 14 days and show no symptoms. We also see people that are asymptomatic that actually never have any symptoms who are also virus spreaders as well.”

The pandemic has provided Imgrund a unique opportunity to use his skills and knowledge in the fields of both math and science.

Imgrund graduated with a biomedical science degree at Guelph University, where he took classes in epidemiology and did a third-year research project with the Public Health Agency of Canada, mathematically modelling the bacterial diseases of campylobacter and e coli.

Following the project, he was retained by Health Canada to continue providing data analysis of infectious diseases.

You can follow Ryan Imgrund, and the pace of the pandemic in York Region and Ontario, on Twitter at @imgrund.




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