Earlier today I went for an asymptomatic test for SARS-CoV-2, the virus responsible for the Covid-19 pandemic. Even though I don’t have any symptoms, my workplace is offering asymptomatic tests as we try to bring more and more people back into the offices and labs. This is especially important as we are now learning that many people with SARS-CoV-2 do not realize they are infected, even though others they infect may not be so lucky.
For the test, a very thin stick with bristles at the end is inserted up the nose and into the septum, twirled, and then removed. It is a very strange sensation — not painful, but the type that makes you want to sneeze and briefly makes your eyes water. The thin stick is placed into a tube, stored on ice, and then sent off for detection.
As cases in Elko increase, you or someone you know has probably considered getting or been asked to take a Covid-19 test. How do these tests work, how specific are they, and what do they tell you about your current health? Let’s take a look:
Nasal/Throat Swabs: test for active infection
Tests that swab the nose or throat check for current Covid-19 infection by determining if components of the virus are currently being expelled through your mouth or nose. These swab tests check for RNA: the genetic material in the SARS-CoV-2 virus. You might have heard of forensic scientists amplifying DNA samples from crime scenes to identify suspects. The RNA test works in a very similar way. Just as there are stretches of DNA that are unique to individuals and can be used to determine if they were at a crime scene, SARS-CoV-2 contains stretches of RNA that are unique to the virus and can tell you if you are currently infected with Covid-19.
Accuracy: Despite some misconceptions that floated around saying that a positive test could come back for someone with the common cold, the test is highly accurate because it looks at the genetic material of the virus itself. Just as DNA can distinguish between two suspects at the scene of a crime, RNA can distinguish between different types of viruses. This means that even if you’re infected with rhinovirus (causes the common cold) or influenzavirus (causes the common flu), the test will come back negative for SARS-CoV-2. Although some of the symptoms for the common cold, flu, and Covid19, might be the same, the genetic information the viruses is distinct.
Downsides: While the nasal and throat swabs seem to be very accurate, they require specialized equipment to determine if SARS-CoV-2 RNA is present. This has led to delays in getting back test results, as well as limited the number of tests that can be performed.
Antibody Tests: test for past infectionAntibody tests are less common and perhaps less useful at the moment as they are more likely to indicate if you’ve been infected with SARS-CoV-2 in the recent past rather than if you have an active infection. This is because these tests check for antibodies: Y shaped proteins found floating in your blood that your immune system will produce in response to SARS-CoV-2 infection. You can think of antibodies as wanted posters hung up by your body after an infection has occurred. Much like wanted posters help to identify criminals that have already been seen, antibodies very specifically recognize a given virus and indicate the virus has been in your body in the past.
Accuracy: As the test looks for antibodies which the body only produces in response to SARS-CoV-2 (as opposed to the rhinovirus or influenzavirus mentioned before), it is highly accurate. Some studies indicate that infection with other coronavirus (including SARS) can lead to false positives, but in places where outbreaks of SARS and other coronaviruses are pretty much nonexistent (including the United States), this risk is low.
Downsides: The tests require a blood sample and specialized equipment to look for the antibodies which means that it isn’t widely available. In addition, the test doesn’t provide much information on current infections as antibodies are usually produced by the body days to weeks after infection by the virus. However, the test is very useful for determining if someone was infected previously with SARS-CoV-2, even if they did not have symptoms at the time. Unfortunately, it isn’t clear yet if previous infection by the SARS-CoV-2 virus means you are now immune to Covid-19. This is something scientists are still working hard to understand and means that previous infection does not guarantee future immunity.
Saliva Tests — a recent addition
A few weeks ago, Yale School of Public Health released the SalivaDirect COVID-19 test, which was quickly approved by the FDA to detect current SARS-CoV-2 infection. The tests are being rapidly distributed for use by schools and businesses. Many of the saliva tests work similarly to the nasal/throat swabs, looking for SARS CoV-2 RNA in saliva rather than deeper in the nose and throat. These tests offer several advantages: they avoid the tickling sensation from the nasal swab, patients can easily spit into a tube without help from health care workers which protects them from exposure, and the tests are highly available in large numbers as there is no sterile swab required for collection. However, in an effort to return test results faster, some of the saliva-based tests are using less direct methods to check for SARS-CoV-2 RNA which will impact how accurate the tests are.
ConclusionsHalf a year into the Covid-19 pandemic, tests for symptomatic and asymptomatic individuals are becoming much more common and widely available. The majority of tests look for active infection by determining if SARS-CoV-2 RNA is present in the nose, throat, or in saliva. This makes the tests highly accurate at determining if SARS-CoV-2 is present, as opposed to viruses responsible for the flu or common cold. As cases continue to rise and schools and businesses attempt to reopen, frequent testing will likely play important roles in limiting Covid-19 spread.
Hannah Margolis is a postbaccalaureate researcher at the National Institutes of Health with a degree in biochemistry from Dartmouth College. She can be reached at firstname.lastname@example.org.
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