So you think you have COVID-19 and you want to get tested. Your first problem
might be finding a test depending on where you live and how sick you
currently are. A recent survey conducted with administrators from 323 hospitals
across the United States found: "hospitals reported severe shortages of testing
supplies and extended waste for test results limited hospitals ability to
monitor the health of patients and staff." Adding: "they were unable to keep up with
testing demands because they lacked complete kits and/or the individual
components used to detect the virus." But let's say that you can actually get a
test for COVID-19. When testing first began the U.S. in January there was only
one type of test that could confirm COVID-19. It relied on a process called
RT-PCR, or reverse transcriptase polymerase chain reaction. This process
isolates and amplifies the viral code of SARS-CoV-2, which is responsible for the
illness we call COVID-19. Many of the tests completed since that day have used
RT-PCR, which typically takes over an hour to produce a result. Now there are
several tests out there using different methods and taking varying amounts of
time to return results. So why are there different approaches
and how they all work and how might testing help us with the global pandemic?
Let's start with how the virus is collected from your body. Many tests for active
COVID-19 infections start with taking a sample from your upper respiratory tract
where the virus is known to reside. This means pushing and collection swap deep
into your nose, throat, or nasopharynx, the space that connects the two.
It's time to analyze your sample. Let's start with the PCR part or the polymerase
chain reaction. It requires that samples be processed by trained technicians on
specialized machines and testing with laboratories. That means patients and the
machines that test their samples are potentially far apart.
That transit time can add hours or days to getting resultsback especially the testing facility
isn't close or if there's a backlog in testing. But when analysis begins the aim
is to amplify the viral genetic code. That code is a single strand of RNA.
But the viral RNA must first be isolated and extracted from your own cells.
Once isolated the small amounts of viral RNA must be amplified to detectable levels.
That's where the RT or reverse transcriptase comes in. It takes a single
stranded viral RNA and uses it as a template to produce double-stranded DNA.
That DNA is then copied over and over using the PCR or polymerase chain reaction.
PCR does this by using cycles of heating and cooling.
it breaks apart the double strand.
added chemicals called primers seek out specific genes
or portions of that now separated DNA.
RT-PCR tests can target different current or virus genes that do different things to help the virus replicate.
Some of those genes help decree the virus's outer protein envelope.
Some make a spiky surface proteins.
The point of this whole process
is to exponentially increase the viral DNA with every heating/cooling step.
After many cycles of PCR one section of viral DNA in the sample would turn into
millions or billions.
Large analysis machines could also run multiple samples at once.
Even they take a few hours to process many results are returned at one time.
The results of the test will still be collected and communicated back to you.
This causes another delay in getting your COVID-19 diagnosis.
But while the bulk of continued COVID-19 testing will probably happen this way new kinds of
tests are starting to show up.
On February 29th, 2020, the FDA issued an
immediately in effect guidance that allows laboratories to submit rapid
rapid SARS-CoV-2 diagnostic tests to be approved for use under an emergency authorization.
This includes several so-called point-of-care diagnostic tests.
Some of these are just smaller versions of the RT-PCR machines but with
prepackaged primers so that any healthcare worker can run the sample as
long as that person's facility owns a company sample analysis machine.
One of these rapid Diagnostics uses a method called isothermal amplification.
Recently president Donald Trump mentioned one company developing this
new kind of test.
TRUMP: On Friday the FDA authorized the new test developed by Abbott Labs that
delivers lightning-fast results in as little as five minutes. It's a whole new ballgame.
The testing machine is small which means it can be located in
hospitals and doctors offices and isothermal means it detects the virus
without having to go through the time-consuming heating and cooling
cycles of PCR uses. Under the hood of this test is something called a nicking
enzyme amplification reaction or NEAR.
It uses primers to target pieces of the
SARS-CoV-2 viral code to make more copies with a kind of genetic copier
printer template.
Added enzymes find the copied pieces of viral code and nick, or very
selectively cut the replicated viral code out of a template like a paper
cutter at the end of our printer.
And this printer prints from both ends so it
spits out two new viral sequences with every new print operation.
Each piece of viral code in your sample can be harnessed by these double ended genetic copier printers.
This means both the printers and the copies from them
rapidly increase if they detect coronavirus RNA.
Each new viral sequence copy also gets a fluorescent beacon. It's like it leaves
the printer with a streak of glowing highlighter on it.
This rapid copy print
of viral sequences is what allows for a positive ID of COVID-19 in just a few minutes.
As of mid-april USA Today reported that the company had shipped
about 500,000 of the rapid tests which run on instruments that sell for $4,500
a piece to all 50 states Washington DC Puerto Rico and the Pacific Islands.
The last type of test is a blood test and is critical for finding out how many of us
have been infected and perhaps who might be able return to work and when.
It's called an antibody test, immunoassay, or serologic test.
It works by identifying some of your body's own defenses against the virus called antibodies.
These proteins called immunoglobulins only exist inside of you if you've mounted an
immune response to the coronavirus.
These tests often use a portion of the viral code
to search for these antibodies in your blood.
It's important to know that these tests are not replacements for the swab based
test for active infections.
The US FDA says as much citing the delay between
onset of infection and antibody build-up.
These tests do Excel a finding out who has already been infected.
Knowing how many of us have been infected and fought
off the virus sometimes with mild or no symptoms is critical for a long-term
disease surveillance.
And if you've already had COVID-19 and lived through it
your body may know how to fight off the infection in the future at least for
some period of time.
Exactly how long immunity might last is an open
question though it raises the possibility for those who've recovered
returning to normal work and contact with others.
Also if your immune response
was strong enough at beating back the virus you may carry effective antibodies
in your blood.
Those would be useful to others with
weaker immune responses to the virus.
In fact the FDA recently designated
so-called convalescent plasma as an investigational product for critically
ill coronavirus patients.
This plasma could also help in the development of effective vaccines.
Regardless of what test you take for COVID-19
in the coming months what remains clear is that all of these methods
will be necessary to beat the coronavirus and end the pandemic