Updated guidelines on home COVID tests explained by public health expert

Host Amber Smith: Upstate Medical University in Syracuse, New York invites you to be "The Informed Patient" with the podcast that features experts from Central New York's only academic medical center. I'm your host, Amber Smith. To determine if they're infected with the virus that causes COVID-19 during the pandemic, people have typically sought out either PCR testing through a laboratory or rapid antigen tests done at home. Those rapid tests are popular because they're so convenient. But a group of researchers at Upstate has analyzed the use of these tests to screen people who are asymptomatic -- and the results have not been good. Now the government has issued some new guidelines about how to use those tests. Here with me to explain is Dr. Chris Morley. He leads the department of public health and preventive medicine at Upstate. Welcome back to "The Informed Patient," Dr. Morley.

Chris Morley, PhD: Thanks for having me back, Amber. It's always a pleasure to be with you.

Host Amber Smith: Now, before we get into the study, can you explain why this is important now? Because I feel like a lot of people think the pandemic's over.

Chris Morley, PhD: Sure. And thank you for giving me the opportunity to say so. Unfortunately we in public health have been saying all along that as long as there's still viral transmission, we're going to see new variants and those variants will produce new spikes. And we have some precedent for that. For example, the 1918-1919 flu actually took about 10 years or so to fully abate as an epidemic. They were still seeing peaks and valleys for some time after the full wave. And that's kind of where we are now. We are still seeing surges, and we saw one here in Central New York that was caused by a novel variant that seems to have emerged here, or at least been first detected here in Central New York.

That was the BA 2.1 variant. And that caused a spring spike. When other places were seeing a lull, we still had a lot of cases. And eventually it turned out to be a new variant. And that's largely happening right now, as we speak with the BA 5 variant. And what happens is every time there's a new transmission of the virus, the virus replicates. It makes millions and billions and trillions of copies of itself, and every one of those copies can carry mutations. All you need is one or two of those mutations to matter, being more infectious or more dangerous, to get around our immunity. That produces a new spike. And so we are still seeing new cases. We've got about 130 to 135 cases a day that we are identifying, even with less testing here in Onondaga County, for example, as we speak.

Host Amber Smith: Well, let's talk more about this testing. Rapid antigen tests: How are they designed to work, and how do they compare with the PCR tests?

Chris Morley, PhD: The antigen test essentially, everything that's marketed now uses a nasal swab, and they look for, essentially, proteins that are on the viral shell. When the test finds those proteins, it basically lights up on a little cassette, or card. So basically what you need is, you need enough virus to be detectable. So the antigen tests work when you have a fairly, relatively high viral load, and there's implications for that. And I'll explain that in a minute. But first I want to compare that with PCR, or polymerase chain reaction, if anybody's wondering what PCR stands for. But the polymerase chain reaction, or PCR tests, essentially take either nasal swabs or saliva in this case. A number of good saliva tests are also available. And what they do is they look for the RNA that is encapsulated within the viral shell. And the PCR procedure replicates that RNA and makes millions and millions of copies of the RNA. So that basically you need much less of that RNA floating around in order to detect it. So the PCR procedures tend to be much more sensitive.

And what this works out to in practice is that the antigen tests do a pretty good job if a person is symptomatic. if you have enough of a viral load to be symptomatic, you have a better chance of testing positive. They also, once you've shed that actual viral particle mass, they tend to fade off and not test positive once you've basically cleared the infection. But there's a much narrower window when those tests actually can detect whether you have a virus in your system or not.

Compare that with PCR, which amplifies the nucleic acid. PCR can detect an infection much earlier, in presymptomatic phases, as well as detect -- this is where a problem comes from and people get confused -- often we have viral debris, like pieces of RNA that still float around in your system, and a PCR test can amplify that long after you've cleared infection. So people early on in the pandemic before we understood all of the dynamics, were talking about people still testing positive. And so PCR, we've refined the protocol, so that's not much of a problem anymore. But the bottom line is when people get confused, the antigen tests typically have a very narrow window when people have the highest viral load. And PCR can detect much earlier and a little bit later, actually. And what that ultimately works out to is that we consider PCR to be the gold standard. It's much more sensitive, which means it can pick up the infection much more easily. Whereas antigen tests are less sensitive. But both are very specific. If you're positive on either you are probably infected.

Host Amber Smith: Now in recent days, the FDA (Food and Drug Administration) and the CDC (Centers for Disease Control and Prevention) issued guidelines about the rapid antigen tests, telling people to repeat testing if they get a negative result, regardless of whether they have symptoms. Do you think someone in the government read your study?

Chris Morley, PhD: I think we're all reading the same studies, and our paper was actually a rapid review of 11 different published studies on four different brands of rapid antigen tests or RATS, we call them. But the bottom line is that the evidence converges that essentially, there are still a lot of uses for antigen tests, but what the FDA clarified in its recent communication is that for you to really avoid that false negative and the false sense of security that comes with finding a negative, when in fact you may be carrying the virus, is that you should find that window I just described when you are actually carrying enough virus for an antigen test to detect by serially testing. We call serial testing the use of several tests in a row. And now the FDA clarified. They typically want people to test at least twice with a 48-hour window. And in some cases, where you really think you've been exposed, to test as many as three times with 48 hours in between. Hopefully, if you are carrying the virus, by doing so serially, you will eventually find that window where you're most able to detect the infection with a rapid antigen test.

Host Amber Smith: This is Upstate's "The Informed Patient" podcast. I'm your host, Amber Smith. I'm talking with Dr. Chris Morley. He's the chair of the department of public health and preventive medicine at Upstate, and we're discussing a study he was involved in that looked at the reliability of rapid COVID tests. So what made your team want to look into this issue? And what was your overall conclusion in your paper?

Chris Morley, PhD: The core issue is that rapid antigen tests are good for some things, and we can talk about when it's appropriate to use them. But your question begs, why we would look and what really predicated our study. And that's the fact that PCR involves a laboratory. You need a laboratory. There are some home tests, but they themselves are very expensive. So for all intents and purposes, most PCR happens in a laboratory. You need a laboratory staff, and you need to run a PCR procedure, which can takehours to days, depending on the backlog in the lab. It takes lots of reagents. It's expensive. So there's a lot to a PCR, which is the gold standard.

And when we were looking at large institutions, particularly educational institutions like colleges that were doing screening of asymptomatic people, basically everybody was required to submit some testing, and some places were doing it twice a week. Here at Upstate, we were doing it every week. Everybody on campus had to submit a PCR swab every week. There were campuses that found that both infrastructurally, logistically and financially compromising and were asking, "Hey, can we just use these much more affordable and quicker, more rapid antigen tests to achieve the same result?"

Now, the problem is that if you are using a once-a-week protocol with an antigen test, you are not serially testing, and furthermore, you are increasing the chance that people will be having false negatives. Not only will that identify fewer cases -- somewhat defeating the purpose of systematic screening -- but you'll actually create another adverse consequence where people who test negative believe that they've gotten a negative test, and they're free, which with a PCR, because it has that much wider window, the earlier detection capacity, they might have had some ability to believe that they're infection free with a PCR for at least a few days between tests. Whereas a negative antigen test would convey essentially. A false sense of security and let them behave in ways as though they were virus free, when in fact they may not have been. So it was not only not a very effective alternative the way we were doing asymptomatic screening, but it also had potential problems as a result.

Host Amber Smith: So what is the best strategy for institutions, or for individuals, to make use of rapid antigen tests?

Chris Morley, PhD: Rapid tests are really good in a couple of circumstances. And I'll tell you, I'm not just describing what the FDA recommends. I am describing how I, as a scientist and public health expert, have been using this with my own family and in my own gatherings and even within my own department. So one of the notable features of a rapid antigen test is that it probably is better at detecting a high viral load when you're most infectious. So if you were to use an antigen test, for example, if you're going to go into an environment where you're going to gather with other people, using an antigen test the same day, or even right before that gathering, it's not a 100% guarantee that nobody in the room is infectious, but if everybody antigen tests, some people might be infected, but you probably don't have anybody with a high viral load and massive amounts of shedding. So if you have a room where everybody, or at least most people are vaccinated and people are generally cautious, and everybody does an antigen test, you're probably not going to have a super spreader event. You might not have any spread, if people use an antigen test in that environment.

They're also good if you have to make a rapid assessment, if you have had an exposure and you don't want to go out and find a PCR test right away, or you can't, or you really need to know what's happening right this second. Initiating a series of rapid antigen tests can give you a lot more information that isn't available to you if you have to make an appointment and go find a PCR and then wait for the results to return.

What I generally have used them in an institutional setting is, if we're gonna have an in-person meeting, I do ask that people antigen test the same day. I'm actually about toattend a small meeting with a couple of colleagues, and I actually did my own antigen test today. And I paired that with a PCR earlier this week. When people have had exposures, we've aggressively used antigen tests for several days in sequence, often paired with a PCR, and that gives you a fair amount of assurance that somebody who's been exposed hasn't picked up the virus. So there's still a lot of uses, both in an institutional setting and for individuals. We keep a stock at home for that very purpose.

Host Amber Smith: I think a lot of families maybe have a stash of these at home. When they became available, people ran out and got them. But as we go into the third school year of this pandemic, what do you advise families about the use of these rapid tests in their home?

Chris Morley, PhD: Well, I do want to recognize the practicality of keeping a large stash. The federal government was handing out, I believe it was eight per household. They're also available widely in pharmacies now. They're fairly easy to come by. What I would recommend is that if families want to be as careful as possible, I would do two things. First of all, we're coming not only upon school season, but we're coming up on allergy season, and that brings two different things. That brings sinus conditions like congestion, runny noses, coughing, due to allergies as we enter the fall. It also puts children in proximity to other kids in closed settings where other things like RSV, (respiratory syncytial virus) other cold-producing viruses can occur, and we will enter flu season at some point as well. So basically, having tests on hand to make sure that what you're dealing with isn't the SARS COV 2 virus, COVID-19, is important.

And, well, if a lot of people are immunized and we're seeing more people have better health outcomes, why do we care if it's not the flu and it's COVID-19, or it's not the common cold and it's COVID-19? Well, the bottom line is, it still actually is hospitalizing more people than the flu and a lot more people than the cold. So while many people experience this as a bad cold, or a flu-like condition, it is still actually leading to more hospitalizations and more long term adverse outcomes than either of those. It's not everybody, but it's still higher. And so those people can still infect others who are at higher risk for those adverse outcomes.

So if you're trying to rule out symptoms, I would still behave differently. If you think you have allergies or a non-COVID produced sinus infection, I would behave differently. I still don't want to spread those other things, the infectious components of those to other people, but I would behave much differently and actually isolate and follow isolation guidelines if it was COVID. I might not be as stringent if I knew it wasn't due to COVID.

The other thing to do is if you've been exposed, you might want to know more quickly, because if you have a child who comes home from school and says, "Hey, Jenny or Johnny was out today, and it sounds like they had a really bad cold and they're out for a while," you might want to test your child or test the whole household because you might not want to then bring your child around their grandparents, for example. So there's still extra caution we should exercise, and having a stash of tests either to rule out symptoms or to test post exposure or for that situation where I just described, if you're going to be gathering with people, having everyone able to test before you gather, would all be safer ways to operate even now, in this post vaccination phase of the pandemic.

Host Amber Smith: Well, thank you so much for making time for this interview, Dr. Morley.

Chris Morley, PhD: Oh, it's been my pleasure. It's always nice to speak with you.

Host Amber Smith: My guest has been Dr. Chris Morley, who leads the department of public health and preventive medicine at Upstate. "The Informed Patient" is a podcast covering health, science and medicine brought to you by Upstate Medical University in Syracuse, New York, and produced by Jim Howe. Find our archive of previous episodes at Upstate.edu/Informed. This is your host, Amber Smith, thanking you for listening.