98ºF

What you need to know about COVID-19 testing according to UT Health experts

A negative result does not mean you don't have COVID-19

A technician shows a nasal swab used for COVID-19 testing. (AP Photo/Jean-Francois Badias)
A technician shows a nasal swab used for COVID-19 testing. (AP Photo/Jean-Francois Badias) (Copyright 2020 The Associated Press. All rights reserved)

SAN ANTONIO*This article was initially published on UT Health San Antonio’s newsroom website and was republished on KSAT.com with permission from UT Health.

Confused about whether you should get tested for COVID-19? There are a few things infectious disease experts want you to know.

Testing is available to anyone but should be reserved for those who have symptoms or who have been exposed to someone with the virus. A person is considered at high-risk for exposure if an infected person has been within six feet for at least 15 minutes and was not wearing a face mask.

Related: Where you can get tested for COVID-19 in San Antonio, Bexar County

To have the most accurate test results possible, wait eight days after exposure to get tested. That’s when the likelihood that a person will have a true positive test result is highest. Any earlier than that, and the virus may not have had a chance to replicate in the nasal cavity or throat and become detectable. Tests will not be positive until there is an active infection, so testing too early could yield a false negative.

“The problem is, in my opinion, a lot of people do not know when their exposure was,” said Ruth Berggren, MD, professor of infectious diseases in the Long School of Medicine at UT Health San Antonio. People may also give a false report about the date of their exposure to get a test done sooner, she added.

People who have active symptoms should not wait to get tested, stressed Thomas Patterson, MD, professor of medicine and chief of the Division of Infectious Diseases.

“Symptomatic people should be tested at any day after the high-risk exposure,” he said. “Asymptomatic people with high-risk exposure can be tested after eight days, but a negative test does not allow an end to quarantine or allow a return to work until 14 days after the exposure.”

The incubation period of the coronavirus is estimated to be two to 14 days.

There are two types of tests, a polymerase chain reaction diagnostic (PCR) test, which uses a 6-inch-long swab inserted into the nasal cavity, and antigen tests, conducted through a blood sample. Antigen tests yield results in minutes but are low sensitivity to the coronavirus and may give a false negative result. PCR tests results take longer but are more sensitive to the coronavirus and more accurate.

“COVID-19 tests are important tools for diagnosing infection, but there are limitations to any test,” said Jason Bowling, MD, associate professor of infectious diseases. “These tests work best in diagnosing people who have symptoms of COVID-19 infection.”

The bottom line, they say, is to reduce the risk of exposure to the virus by wearing face masks and maintaining a physical distance of at least six feet.

Dr. Bowling answers more of your questions below.

Who should get tested?

Anyone who develops new symptoms after an exposure to someone with COVID-19 should get tested. People who have been exposed to someone with COVID-19 but don’t have symptoms can consider testing but should wait until the right time to prevent inaccurate results.

When should I get tested?

If you have symptoms concerning for COVID-19, you should get tested. After exposure to someone with COVID-19, you are at potential risk for developing infection for 14 days after the exposure. If you have been exposed to someone with COVID-19 but don’t have new symptoms, it is important to wait for eight days after the exposure to reduce the chances of an inaccurate test.

Why should I wait to get tested?

It takes time for the SARS CoV-2 virus that causes COVID-19 to become detectable, even with the sensitive tests being used. For example, getting a test the day after an exposure gives you a 100% chance of a negative test even if you later develop infection.

Where should I get tested?

Several testing sites are available throughout the San Antonio area and are listed on the San Antonio Metropolitan Health District website: List of Testing Locations in Bexar County.

It is not advised to go to the emergency center at a hospital just for testing. Emergency centers at hospitals throughout the city are very busy taking care of symptomatic patients with COVID-19. If you go to one of these centers for testing, you might potentially become exposed to someone with symptomatic COVID-19 disease waiting to receive medical care.

What does a negative test result mean?

If you are asymptomatic but have been exposed to someone with COVID-19, it means that you don’t have detectable COVID-19 at the time of the test but it doesn’t change the 14-day window of infection risk you have from exposure. You should continue to monitor twice daily for fever and symptoms for the full 14 days.

What does a positive test result mean?

You have detectable COVID-19 and can potentially transmit infection to others. You should self-isolate and follow the instructions provided by the testing site that has provided your results. Additional information on what to do can be found on the Centers for Disease Control and Prevention website: What to do if you are sick.