Timing may be critical to accurate COVID-19 test results

COVID-19 False Negatives test warning
Free COVID-19 testing site in the city of New Orleans.
Free COVID-19 testing site in the city of New Orleans. (Source: WVUE)

NEW ORLEANS, La. (WVUE) -Many communities are seeing a crush of people wanting to be tested for COVID-19, but some people could benefit from not rushing to be swabbed, according to public health experts.

Dr. Susan Hassig is a Tulane University epidemiologist and associate professor of epidemiology. She commented on what could contribute to false-negative test results.

“They’ll get a negative result, you think, oh great I’m not infected but in fact you may be and it’s just that the test was not able to find the virus in the sample that was taken because the amount of it was too small to be detected by the test,” said Hassig.

The virus operates by its own clock inside the body.

“There’s a process the virus goes through as it interacts with its human host involving how it reproduces itself, it takes some time for it to build up kind of a critical mass that can be detected by the test and so testing too early after exposure can result in someone who actually is infected getting a false-negative result,” Hassig said.

And that could have consequences that concern public health experts.

“Maybe they’re not so careful about wearing a mask, staying separate from people physically, and may engage or go, you know, visit a relative who is perhaps vulnerable for serious consequences if they become infected and yet they are in fact capable of transmitting the virus,” said Hassig.

She was asked how much of the virus must be present in the body to make someone contagious.

“As far as we know it takes relatively small amounts of the virus in a person’s respiratory tract for them to be able to shed it and transmit it, the challenge is our testing methodology isn’t good enough to necessarily find that level of virus. So, that’s why we believe in fact that people may be shedding virus for a couple of days before they actually are able to test positive,” answered Hassig.

And she said following recent local protests related to George Floyd’s death some participants contacted her with questions about whether they should be tested for the novel coronavirus.

“Because they were concerned, they knew they were very close to people, there was a lot of shouting and singing and talking and everything else and my recommendation to them and to everyone who I talk to about this is you should wait for at least five days after you believe you might have been exposed before you even think about getting tested because that’s what we are seeing in the evidence that we’ve been able to gather about how long it takes for enough virus to generate that the test can identify,” Hassig said.

Dr. Joseph Kanter, Assistant State Health Officer at the Louisiana Department of Health, stressed that anyone who has been exposed to the virus must self-quarantine.

“The people that have an exposure, they have to quarantine for 14 days regardless of whether or not they get a negative test during that time and the reason for that is the virus replicates and when it has enough in your body it becomes detectable but we don’t know exactly when it’s going to replicate to that degree,” said Kanter.

Hassig said there is solid evidence that large numbers of people do not experience symptoms of the virus and could be unaware they are “shedding” it.

“We have seen repeated evidence in a variety of different places all around the world that there is probably a substantial portion of people who are infected with the virus who may in fact never develop an illness they would recognize as being something to be concerned about and so it is those people who we believe may be very much responsible for a lot of the violent spread that we see happening in communities,” she said.

Hassig believes people who are tested when they are exhibiting COVID-19 symptoms have less chances of getting flawed results.

“If symptomatic with, you know, the shortness of breath or the loss of taste and smell that is generally when people, if people become symptomatic and they get tested they will get a positive test, they are much less likely to have a negative test,” Hassig stated.

And she urged everyone to function as if they have the virus, test results or not.

“The bottom-line and the first line of defense is we all need to act as if we are infected, we all need to wear a mask because the mask protects others from the virus you might be shedding and you need to keep that physical distance,” said Hassig.

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