A biostatistician breaks down the risk of COVID-19 exposure in Ontario

Ryan Imgrund, who tweets daily risk-management assessments for Ontario, discusses what he's seeing in the stats

Ontario is in stage 3 of reopening, and – at least at the time of this writing – it’s going pretty well. The daily increases in new cases have largely stayed below the 100 mark for the past two weeks. We’re by no means free of COVID-19, but we seem to have avoided the spikes in cases seen when bars, movie theatres and restaurants have reopened around the world. So is it safe to go out and do stuff? How can we calculate our COVID-19 exposure risk?

Ryan Imgrund, a Newmarket high-school teacher and hospital biostatistician at Southlake Regional Health Centre, has been tweeting daily assessments for COVID-19 exposure risk in Ontario by township, recently expanding his beat to include comparisons to the rest of the world. We talked to him about what he’s seeing in the stats.

Follow the science

Math is turning out to be very comforting right now. 

It works out really, really well for the education of the public too, because there’s a lot of misunderstandings about probability and some other things like that. It’s been nice to do social discourse online and be able to educate people about this stuff. There are a lot of misunderstandings out there.

How do you get people to believe your findings?

One thing I always do is I always answer questions. That’s an important thing, because a lot of people have valid questions. “Why is this this way? Why is that that way?” 

How is it that we aren’t experiencing a new surge of cases now that people are dining in restaurants and going to gyms? Everywhere else those things have resumed has seen an uptick in cases, but Ontario hasn’t experienced one.

We are doing many things right. We have 33 of 34 public health units mandating masking indoors [as of August 10]. Those masking mandates now actually cover 99.2 per cent of Ontario’s population, which is fantastic. I think that’s why worldwide, Ontario is on the lower end of cases. We’re down there with Taiwan, China, South Korea, New Zealand – very, very good company to be keeping these days. 

Why contact tracing matters

The most insidious advantage of COVID-19 is that 40 or 45 per cent of people are completely asymptomatic. Most of those people won’t think to get tested. Has our understanding of where to look improved as time has gone on? 

It certainly has. Early on, we thought this was much like SARS: we thought many people would be symptomatic, that they would have a fever one day after transmission. What we seem to be finding is there’s a five-day incubation period and only about 65 per cent of people show symptoms. The fact that we’re only catching one of every four cases means a lot of people [have] symptoms so mild they don’t actually think it’s COVID-19. We are catching a fraction of the cases, and when we catch them, it’s roughly eight and a half days after the transmission event actually happened at that point. And those individuals are only able to transmit for another three and a half days, which is why it is so important to be able to track down those people’s contacts. 

How quickly does public health respond in a situation like this? The government has released a new contact-tracing app. Has that helped yet, or is it too soon to know? 

I’m not too sure. One of the issues with the app is that it’s stuck [determining] transmission events that happen when one cellphone is within two meters of someone else’s phone for 15 minutes. That seems to be a long period of time. But I understand why they’re doing that: they don’t want a phone constantly looking for other phones, wasting battery power [and] then having people erase the app from their phones. What I’m hoping is that it gets better over time, that, you know, maybe after five or 10 minutes, it’s actually able to find someone. That’s the key. We don’t know how long a person has to be around someone else for an actual transmission to occur. And that’s one of the mysteries of COVID-19, too. We simply don’t have answers to that.

This interview is condensed from the August 18 episode of the NOW What podcast, available on podcast platforms everywhere and at nowtoronto.com/podcasts . You can also play the episode below.


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