This week, the Ontario government announced it was rolling out so-called COVID-19 rapid-testing kits to key sites in the province to help combat the second wave. What are these kits? How do they work? And what can, and can’t, they do? To find out, TVO.org spoke with Zain Chagla, a doctor at St. Joseph’s Healthcare Hamilton and an associate professor of infectious disease at McMaster University.
Matt Gurney: I guess we have to start with a basic question: What is a rapid test? How does one work? If I show up somewhere and there’s rapid testing, what do I do?
Zain Chagla: There are two available in Canada now. One is ID NOW. That’s the one that looks like an espresso machine. It does a polymerase chain-reaction test, or a “PCR” test — that’s what we’ve been using at testing centres — but in a rapid manner. It’s still taken to a lab. But it’s ready in about an hour, instead of days. You still need the deep nose swab, but you get the result in an hour or so. This is the test, by the way, that they used at the White House Rose Garden event,with obviously limited success!
Gurney: Yeah, wow. I’ll say.
Chagla: Yeah. But the other one, the one that people are paying more attention to and that Premier Doug Ford was talking about the other day, is the Panbio kit. This really is like a pregnancy test. A nurse or someone still has to shove a nasal pharyngeal swab into you, but, rather than sending it to a lab, they put it in a tube, mix it up with a fluid, and drip it on what looks like a pregnancy test. You will have a result in 15 minutes. It does not require a lab to process it. So both tests have an identical start of the process — you need the deep nasal swab. But with Panbio, there’s no lab, the result is easy to read, and it’s fast. So you could, for instance, get your result while waiting outside a facility and then get a wristband that marks you as safe. And then you could go in.
Gurney: Given all the stories we’ve heard about overwhelmed testing centres, you can see the oous advantage of this. And, presumably, we’ll get more and more of these.
Chagla: Absolutely. There is a downside. We trade a little bit of sensitivity for rapidity. It’s not the end of the world, though. The PCR tests are, in a sense, really oversensitive. There are people with tinfoil hats on Twitter talking about PCR tests picking up the wrong people, but they’re not totally wrong, in the sense that the PCRs can pick up very, very minuscule amounts of virus; they can pick up dead virus.
So if you’re using PCR tests to screen visitors at a long-term-care home, for instance, you could be picking up people who were sick and didn’t know it, say, six weeks before. These rapid tests work best when there’s a good amount of virus there. So they won’t be picking up stray bits of virus that aren’t clinically relevant, they may not pick up people early in their infection, and you might need to wait a couple of days for them to begin showing symptoms. But they will get most people with a good viral load, people that are kind of in the midst of their illness.
So where do we roll these out? We are sending them to the long-term-care homes, and that makes sense. Logistically, I’d rather not wait four days to get a result for someone walking into a long-term-care facility with COVID-19 — I would rather know in 15 minutes, even if the sensitivity is a bit lower.
There are other places with higher-risk populations that could use this kind of screening, when time is of the essence. If you’re in a northern community, you know, it takes five days to get a result back. That’s just too long to work. So rapid tests, with a backbone of PCR testing to actually confirm results when necessary, can be rolled out in a way that makes a big difference, lowers wait times, and encourages more people to get tested.
Gurney: This might be a dumb question, but when you’re talking about sensitivity and errors, what way would the errors skew — false positives or false negatives?
Chagla: With the rapid tests, false negatives. With 75 per cent sensitivity, you’re going to get more false negatives than you’d like.
So what do you do?
There are two main approaches. One is to use the rapid tests in environments where you expect to not find much COVID-19. A negative test in an environment where you believe incidence is low really can be safely read as a true negative. But do you want to use it as a screening tool at a hospital emergency room where people are presenting with coughs? Probably not. In that environment, you have to assume people are positive and rely on the PCR tests to confirm or deny that. But in terms of false positives with rapid tests, that’s possible, but we wouldn’t expect many of those. False negatives are the concern.
Gurney: If the danger is false negatives, does it make sense to do two tests at a time and process them both? If you pass both tests, and each is 75 per cent sensitive, that is a pretty reassuring signal that you are negative.
Chagla: That’s an interesting question. Doing two tests in a row would help eliminate some false negatives, if the problem was either a faulty test or an operator error. Both of those things can happen, and doing it twice might eliminate some of those. But the testing sensitivity issue isn’t really a function of the technology or the process. It’s more about the quantity of the virus. So if you are very early in an infection, a test with low sensitivity might not catch that. But doing two in a row doesn’t change that — you’re using a relatively lower sensitivity test to test the same level of viral load. So, yes, it could eliminate operator errors or faulty tests, but it won’t make it easier to detect early or late-stage infection when viral loads are low.
Gurney: We’ve heard a lot about these tests. They’re being hailed as a major step forward. When announcing that these kits were rolling out, Ford called them “game changers.” I’m curious about that. We’ve talked a bit above about how best to use them — does this really change the game, from a public-health perspective?
Chagla: The big thing right now is making sure that people in long-term care get screened, because you can see the crisis happening in long-term care every day. The people who live in the facilities are the main victims, but they’re not bringing it in. It’s coming in from outside in the community. So rapid tests are perfect for this. You get people tested more regularly, you have testing results that are there quickly, and you’re able to at least make sure people coming into these high-risk settings don’t bring COVID-19. It won’t be 100 per cent effective, but you can check them as often as you can, in a way that won’t overload provincial testing labs, and hopefully keep a lot of the infections in our LTCs down.
There are other high-risk settings where we can use these, too. I said above you wouldn’t want to use these as a primary tool in an emergency room. But you could definitely use them for staff who are working in a COVID-19 ward of a hospital. We have seen massive outbreaks in meat-packing plants. We could bring these in there, or in other similar essential facilities where it’s hard to be physically separated, as another line of defence.
But we can also use them in whole populations, on a postal-code level, right? We have very high infection rates in Peel region, for example. There is a real concern about stigma and about people losing their jobs if they test positive. Also, people don’t want to wait days for results. If we could do large-scale rapid testing and link it to income supports and protect anonymity — so people know they’ll be taken care of if they test positive — and if they also know that everyone else is getting tested, that’s something we could look at.
That’s aspirational for now because we don’t have a sufficient quantity of tests, but this is something we could conceivably do. You might remember that Slovakia did this. They tested every adult at rapid-testing centres in a weekend. Millions of people. They found about 1 per cent were infected, and they isolated those people. They got them out of the population. And it seems to have worked! Now, Slovakia is a small country and has a small population. But on a local level, we could one day do something like that.
Gurney: Let me ask you the reverse of that question: Where will these tests not be helpful?
Chagla: Health-care settings, where you need to absolutely be right. You still need to do the PCR tests there. Like I said above, you can maybe use rapid tests as one line of defence. They can be helpful for screening. But you can’t rely on them in hospitals as your only tests.
But keep in mind that, even with these rapid tests, someone is still doing a deep swab of your nasal cavity. So there still needs to be a nurse or someone involved in that process. So there’s still those limits on where and when these can be used. As much as we’d all love some easy home test we do before heading out the door in the morning, this isn’t that. Health Canada is looking to validate some self-directed tests — things we could mail out to everyone and say, hey, test yourself at home. We’re potentially moving in that direction. But that would require a lot of work to get there. That is also aspirational for now.
Gurney: One last question. Now that Ontario has these tests, are we worried at all about a supply chain for parts, supplies, anything essential? Do we have to ration their use, or can we go nuts where we have them?
Chagla: I’m not aware of any capacity constraints on the tests we have. This is a rapidly emerging global market, and there’s going to be more and more supply coming on and more and more options for Health Canada to validate. These are the first tests we have, but they might not end up being the best ones we use. More will become available. So, yeah, I’m not aware of a constraint, and I’m confident that the availability is going to get better as we go.
This interview has been condensed and edited for length and clarity.
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