Q&A With Dr. Stephen Threlkeld: What You Should Know About COVID-19 Testing

Testing is critical to slowing the spread of COVID-19. We sat down with Dr. Stephen Threlkeld, an infectious disease specialist and epidemiologist who works with Baptist Memorial Hospital-Memphis, to find out what you need to know about COVID-19 testing—including if and when you should get tested.

Q: Who should get tested?

A: Anyone who has symptoms and anyone who has been exposed to an individual who has tested positive for coronavirus should get tested.

Targeted testing of asymptomatic people is very important because it helps determine where the virus is in our community. Recently, it’s been harder for health care labs across the country to obtain the reagents, or chemicals, required to run tests. Every lab in America is having a problem meeting the demand for tests.

For a while in Memphis, there was more supply than demand. That’s changed recently. We need to test more people. At the same time, we are trying to educate people on when they don’t have to be tested.

Q: Should I get tested before visiting my parents?

A: Many different variables go into this kind of decision. Yes, it’s reasonable to test someone before he or she is around elderly or at-risk parents. It’s also very reasonable to try to avoid being around them in the first place.

A test today does not mean that you can’t come down with the infection more than two days from now. We don’t have to do advanced math to determine their statistical likelihood of getting infected from us if we’re not in the same house with them.

Q: Do I need a negative test before going back to work?

A: Some companies might require a negative test before allowing you to return to work. However, the Centers for Disease Control and Prevention has suggested using a time-based option instead.

If your symptoms have been present for at least 10 days, and you are much improved for at least one day—whichever is longer, then you are safe to go back to work. This includes having no fever or having to use Tylenol, Motrin, etc., to get your fever down. This is important because after about nine days, we really don’t find that you shed virus that is contagious to somebody else.

Q: Should you keep getting tested after you’ve tested positive?

A: We don’t routinely recommend that you get tested again after you test positive. We do insist that you isolate yourself from others after you’ve tested positive.

People who test positive fall into two categories: those who are asymptomatically positive and those who had symptoms and got tested because of those symptoms. If you don’t have symptoms but test positive during a screening, you will need to isolate for 10 days after the date that you tested positive.

If you get a test because you have symptoms, then you need to isolate for at least 10 days from the time your symptoms began. You also need to show at least three days of significant improvement in those symptoms. If you feel fine by day seven, you can come out of isolation by day 10 of your symptoms. If you are still sick, you might have to stay in isolation until you improve significantly for at least three days.

Q: Why do people continue to test positive after recovering from COVID-19? Does this mean you still have it?

A: The main test—a polymerise chain reaction, also called a PCR test—looks for a very tiny piece of RNA. That’s the messenger material that handles the genetic information of the virus. Humans have DNA, but this virus uses RNA. As the immune system tackles the virus, the virus gets digested or chopped up into little pieces by the immune system.

After 10–17 days, the particles you cough up or have in your nasal passages are not a whole virus. They are little pieces of virus that can’t infect somebody else. The PCR test can pick up those tiny pieces of RNA in your nose—sometimes for weeks after the infection.

Fragments of the virus are not a danger to others, and they can’t translate into an infection. It takes a lot more than those little pieces to make you or other people sick.

Q: Should I get antibody testing?

A: Antibody tests check your blood by looking for antibodies, which may tell you if you had a past infection with the virus that causes COVID-19. In general, antibody testing is more helpful for analyzing how this virus affects large groups of people than it is for looking at one individual. False positives can occur with antibody testing in individuals.

We don’t want antibody tests to give people a false sense of security or think that they can safely be around people who may have the virus. We still don’t know how or if antibodies protect people. You would not change your behavior based on receiving a positive antibody test. You should still wear a mask and practice social distancing.

Q: What’s the difference between antibody testing and PCR testing?

A: PCR tests determine if you have the virus right now. Antibody tests can help determine if you had the virus in the past. Typically, it takes two weeks for your body to produce enough antibodies to make a positive test.

By the time most people test positive for antibodies, they don’t need isolation anymore. However, it is still very important to continue wearing masks and practicing social distancing.

Q: Is there a new test?

A: Scientists are working on a variety of different tests. We don’t have a new test available yet that is as good as the PCR test. We have some tests that are more rapid, but they aren’t as sensitive.

Q: What is pool testing?

A: Pool testing combines samples from five to 10 people to make one batch test. Health care professionals analyze the batch to see if anyone in that group tests positive for the virus.

If there are no positives in the batch, you don’t have to test those 10 people anymore. If the batch returns a positive result, all 10 samples must be tested individually. Pool testing can save time and resources when the positivity rate is below 10–15%.

Q: What else should people know about testing?

A: If you are not sure if you should be tested, check with your doctor. Those who have been exposed or those who have symptoms indicative of COVID-19 need to be tested.

As we move forward, we need to continue to develop strategies for testing vulnerable populations, such as kids and teachers in schools and people in vulnerable workplaces—like hospitals. It’s important to not only test and document that your workplace is safe, but also to identify pockets of infection that might spread to others. Strategic testing is very important for keeping schools and businesses safe.

Visit our website to learn more about COVID-19. Find a doctor by visiting our Find a Doctor page.