Narrator: Coming up on Mayo Clinic Q&A,
Dr. Matthew Binnicker: The majority of the at home tests,
the vast majority of those are the antigen tests, again looking
for the viral protein in a nasal swab sample.
Narrator: Testing for COVID-19 is part of the overall strategy
to end the pandemic. Using a rapid at home antigen test can
provide quick results, but it's important to understand when and
how to test.
Dr. Matthew Binnicker: What we're recommending is that if
you're performing an at home antigen test that you use the
test exactly as the instructions call for.
Dr. Halena Gazelka: Welcome, everyone to Mayo Clinic Q&A. I'm
your host Dr. Halena Gazelka. We're recording this podcast on
Monday, January the 24th, 2022. Testing for COVID-19 has been a
big topic during the pandemic and very important in helping to
end it. But, understanding the testing, including the type of
tests, how and when to use which test, it's very confusing to
most individuals. And so, here to help us sort this out is Dr.
Matthew Binnicker, who is the director of clinical neurology
at Mayo Clinic. Welcome, Matt.
Dr. Matthew Binnicker: Thanks. Really glad to be here.
Dr. Halena Gazelka: I admit that I think this is an incredibly
confusing topic. And so, I'm delighted that we're going to
talk about this today. Can you tell our listeners, Matt, the
two type of tests that can tell if you have COVID-19, the PCR
and the antigen?
Dr. Matthew Binnicker: There are really two main categories of
tests that are being used currently to diagnose patients
with COVID-19. The first is what I would call molecular tests,
probably better known as PCR tests. And those have really
been the gold standard, the most commonly and frequently used
tests since the beginning of the pandemic. The PCR tests are
looking for the virus's genome, its RNA genome in samples like a
nasal sample that's collected. Those tests are really
sensitive, meaning we can detect really low levels of the virus
in a sample. They're very specific, meaning we shouldn't
get many false positive results with those tests because they
are so specific. Usually, they're sent to a lab. So,
results can take some time, maybe up to 24 hours. And at
some points during the pandemic results were taking multiple
days to get back to patients. The other type of test is what
are known as antigen tests. And those are most commonly being
performed at home by patients. Those look for a viral protein
in the patient sample. So, a nasal swab is collected much
like a pregnancy test, easy to perform, you get results in 15
to 20 minutes. So, quick, easy, but they also have some
important limitations that we can talk about.
Dr. Halena Gazelka: And to add to the confusion, Matt, there is
antibody testing. How does that differ from what you just
described?
Dr. Matthew Binnicker: So, yeah. There are antibody tests, or
serology tests that are looking for antibodies that are
generated by the immune system in response to infection with
the virus. Those tests are good for purposes of determining how
many people in a population were exposed to a virus, or in some
cases how many have responded and produced antibodies in
response to immunization. The problem with the antibody-based
tests is that the antibodies typically take 10 to 14 days to
reach levels that can be detected by those tests. So,
because of that they're not very useful for diagnosing acute
COVID-19 infection. They're better for determining whether
someone's been exposed to the virus kind of after the fact, or
whether they've responded to a vaccination.
Dr. Halena Gazelka: Matt, there's a lot of at home testing
going on now. Are those typically PCR tests, or antigen
tests, or some of each?
Dr. Matthew Binnicker: Yeah, the majority of the at home tests,
so when you go to a local pharmacy and pick up an
over-the-counter test, the vast majority of those are the
antigen test, again looking for the viral protein in a nasal
swab sample. There are, I believe, two options that are
what we call molecular tests, or looking for the viral RNA.
They're very hard to come by. I believe that one of those
requires a physician prescription to get. So, if
you're getting an at home test, chances are it's an antigen test
that typically takes 15 to 20 minutes.
Dr. Halena Gazelka: Because if it was a PCR test, it would have
to be sent to a lab to process, correct?
Dr. Matthew Binnicker: So, those two options that I mentioned,
you can perform those at home. But there also are at home
collection options, so you can collect a sample at home, and
then mail it into a laboratory, so that of the options that are
truly at home tests, those are difficult to find. And there's
only two of those. And then if you're getting a PCR test, but
collecting the sample at home, that's being used more
frequently and kind of provides patients with greater
flexibility, not having to go into a collection site to get
that sample collected.
Dr. Halena Gazelka: So, I've seen news reports about swabbing
the throat instead of the nose. Is this a good idea? Does it
work?
Dr. Matthew Binnicker: Yeah, there have been quite a few
reports on social media is where it started. And then quite a few
news media stories about this. During the early days of the
Omicron surge, what we noticed and have e continued to notice
through clinical experience, is that many patients are
experiencing a sore throat as one of the initial symptoms of
their disease. And so, I think there became some interest in
whether swabbing the throat could detect COVID-19. Now the
tests that were being used were the at home antigen tests, and
all of the at home antigen tests are approved to use a nasal
swab. None of the tests that are currently available for us to
purchase were validated and authorized by the FDA for
testing of throat swabs. So, what we're recommending is that
if you're performing an at home antigen test that you use the
test exactly as the instructions call for, which is a nasal swab.
There's been some reports that, you know, Omicron may be more
prevalent in the throat. Interestingly enough there was
just a study released in a preprint, meaning it hasn't gone
through the full peer review process that compared nasal
swabs against throat swabs using one of the more common antigen
tests and found that throat swabs don't work as well. So,
this is really important not to get your information about
testing off of social media, but really wait for the scientific
data to come out to support the approach we use.
Dr. Halena Gazelka: Excellent point. Matt, to help our
listeners out, I was hoping you and I could go through a couple
of scenarios and you could tell me which test would be
preferable for the individual in that scenario. So, how about if
I'm an individual, I think I've been exposed, but I don't have
any symptoms?
Dr. Matthew Binnicker: So, in that case you've been exposed to
someone with confirmed COVID-19, but you're asymptomatic. The
best approach is to wait three days after that exposure and to
schedule a time to have a sample collected to be sent off to a
lab for PCR. The antigen tests, they don't perform as well in
individuals that lack symptoms because there's nothing to guide
us of when that test should be performed. So, their sensitivity
is lower. It's been shown, the antigen test to be as low as 35
to 40% in asymptomatic individuals, so those that don't
have symptoms. The PCR tests are really the most sensitive
and give us the best chance at picking up those asymptomatic
infections.
Dr. Halena Gazelka: And Matt, may I take that a step further
and ask you, is it advised that if you know that you have had a
close exposure that you be tested?
Dr. Matthew Binnicker: It is a good idea that if you've had a
known exposure that you get tested. Now, there's been some
leniency in the fully vaccinated population. So, if you have been
fully vaccinated, if you're eligible for a booster, you've
received that booster, and you're exposed, it's not a
requirement to test in many situations, but still probably a
good idea. In the unvaccinated population having been exposed
to someone with confirmed COVID-19, yes getting tested,
waiting three days on average, and because it takes some time
for that virus to reach detectable levels is the
recommended strategy.
Dr. Halena Gazelka: Okay, scenario number two, what if I
have COVID symptoms?
Dr. Matthew Binnicker: So, if you have COVID symptoms, so sore
throat, fever, runny nose, congestion, loss of sense of
taste or smell, which is actually we're seeing that less
frequently now with Omicron variant compared to past
strains. But, if you're experiencing any of those, I
think a reasonable first step if you have access to an at home
antigen test, is to perform an antigen test. If you get a
positive result by any of the authorized at home tests in the
presence of COVID-19 symptoms, that's a really reliable result,
and that can inform your decision making about isolating
and not exposing others at work or school. Now, if you test
negative by an at home antigen test, it doesn't mean you're in
the clear. It's important to either perform another antigen
test 24 hours later, or to schedule a time to have a
lab-based PCR performed. The reason why we're recommending in
some situations for the lab PCR to be done if symptoms persist,
is that many of the lab PCR tests that are being used now
test for both COVID and influenza, and we're seeing
quite a bit of influenza in the country as well. And so, the at
home antigen test will miss that influenza possibility, whereas
the lab-based test can cover for the influenza as well.
Dr. Halena Gazelka: And the symptoms are so similar.
Dr. Matthew Binnicker: They are. Yeah, influenza and COVID-19
clinically resemble each other very closely, especially in the
early days after disease onset. So, it's almost impossible to
distinguish the two diseases without a laboratory test.
Dr. Halena Gazelka: Sometimes even common upper respiratory
infections like what we call the common cold sounds like lot of
the same symptoms.
Dr. Matthew Binnicker: That's right. And with Omicron we are
seeing more individuals, especially those who have been
fully vaccinated, come down with very minor illness that
resembles very much the common cold. So, if you're experiencing
a minor sore throat, runny nose, maybe a mild cough, getting
tested for COVID-19 is a really good idea because it could be
COVID-19, even in the presence of mild symptoms.
Dr. Halena Gazelka: Alright, now scenario number three. I've had
COVID-19, and I want to know if I am in the clear to return to
work to school to other activities?
Dr. Matthew Binnicker: Yeah, so in the case of someone having
been diagnosed with COVID 19, there's options depending on
where you work, where you live. The CDC is currently advising
that anyone who tests positive for COVID-19 isolate at home for
a minimum of five days. After five days, they can return to
work, or to school, again depending on the location and
the local guidelines as long as they wear a mask. Now, some
employers are taking it a step further. Whereas after five days
Dr. Halena Gazelka: Matt, I know that here at Mayo Clinic we have
of isolation, they may require a negative COVID-19 antigen test
to return to work. And the reason why some employers are
using the antigen tests instead of the PCR is because a PCR we
know can stay positive sometimes for weeks, and in some
immunosuppressed patients that PCR test can stay positive for
months. So, an antigen test should become negative as the
amount of virus in a person's upper respiratory tract
declines. And so, if you don't have symptoms, your symptoms are
improving, it's been at least five days since you began your
isolation, and you test negative by an antigen test, that
information can be used to help create a safe opportunity to
return to school or work.
begun to provide antigen tests to employees who are on the job
but begin to experience symptoms so that they can test. I imagine
this has something to do with the sheer volume of tests that
are being performed, and I'm wondering what does that look
like? How many tests are you doing during this time?
Dr. Matthew Binnicker: Yeah, you know we've been almost two years
into this pandemic, but it's hard to believe that about a
week ago we did the most tests in the upper Midwest that we had
ever done since the pandemic began. We did close to 40,000
COVID-19 PCR tests at our Mayo Clinic locations in the upper
Midwest in one week's time. Of those we saw about 30% of those
40,000 being positive. So, again really record high positivity
rates. And you're right, the use of antigen testing in certain
scenarios, either someone has symptoms, or they've already
tested positive, or trying to get them back to work safely
really helps to supplement kind of our testing toolbox and
alleviate some of the stress on the labs that are getting, just
again, record high volumes of samples for testing.
Dr. Halena Gazelka: Wow, that's incredible. That's pretty
impressive. I would like to see that all in action.
Dr. Matthew Binnicker: Yes. Yeah, the team is amazing, and
they've continued to put up with a lot of change and just one
challenge after another, and the sample volumes continued to
increase. So, props to all the laboratory staff.
Dr. Halena Gazelka: So Matt, what is the outlook for COVID-19
testing in the future? Do you see it continuing as we are?
Dr. Matthew Binnicker: So, we think that the Omicron surge is
likely going to peak sometime within the next week. And then I
expect cases and testing demand to steadily decline from there.
Now even if COVID-19 levels reach low levels across the
country, so less than 5% positivity rates, there will
still be needs for testing especially in at risk
populations, those undergoing high-risk procedures and
surgeries. And then as the virus kind of enters into more of an
endemic state where we're seeing predictable geographically
defined outbreaks, kind of like what we see with influenza every
year, we'll still need to test for COVID-19. And I envision
that if you have symptoms, a respiratory infection in the
winter months, in the future you're probably going to get
tested for COVID-19 and influenza, again because it's
very difficult to distinguish the two based on your symptoms
alone, how we manage you with antiviral treatments, or
different management strategies is different depending on which
virus you have. So, I see COVID-19 testing here to stay,
and it will probably be included in symptomatic individuals for
years to come.
Dr. Halena Gazelka: Well, thank you Matt. This has been a really
enlightening and informative discussion. I appreciate it.
Dr. Matthew Binnicker: Oh, again glad to be here, and it's a
constantly evolving situation. But I think something that we
have, the teams have responded to and continued to help to
provide care for our patients. So, thanks for having me on.
Dr. Halena Gazelka: Yeah, thanks for all that you're doing to
help with the pandemic. Our thanks to Dr. Matt Binnicker,
director of clinical virology at Mayo Clinic, for being here to
help clear up our questions about COVID-19 testing. I hope
that you learned something. I know that I did. And we wish
each of you a wonderful day.
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