A negative test result is a welcomed finding when it comes to COVID-19, but just because you aren’t positive for the novel coronavirus doesn’t mean you’re in the clear, experts say.
Furthermore, testing negative for the novel coronavirus is not an excuse to throw a large indoor party or ignore public health recommendations.
“The negative test is not something that should be changing people’s behaviour,” said Dr. Peter Phillips, a clinical professor of infectious diseases at the University of British Columbia.
“A negative test doesn’t mean that we’re not incubating (COVID-19)… It does not provide the answer that people would like it to give you.”
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Some people may have misconceptions about how coronavirus tests work and what they actually help determine, said Dr. Dominik Mertz, an associate professor of infectious diseases at McMaster University.
“People (think) it’s actually a test to rule out that you’ve got infected — it’s not,” Mertz said.
“They can only rule out that you currently don’t have virus in your nose that’s replicating, which only starts a few days before you become symptomatic.”
You could test negative but still have the virus
COVID-19 typically has an incubation period of five days but can range from one to 14 days, according to Health Canada, so it could take time from the point of infection for a person to actually test positive, Ashleigh Tuite, an epidemiologist at the University of Toronto, previously told Global News.
“Even if you get a negative test result, it doesn’t necessarily mean that you are not infected right now,” Tuite said.
Phillips explained that when you are first exposed to the coronavirus, it takes a few days for the virus to take hold and become detectable by a test. People often don’t just contract the virus and fall ill right away.
“If exposure was on Monday, the odds of the test being negative are very high on Tuesday and Wednesday… the test is not going to pick it up,” he said.
“Somebody who’s going to become symptomatic around Day 5 might test positive for (the coronavirus) within a day or two before the onset of symptoms.”
Data backs this up: a recent U.S. review on the accuracy of RT-PCR tests, a common coronavirus test, found that you can test negative even if you have the virus, depending on when you get swabbed.
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Researchers found that the probability of a false negative before someone starts showing symptoms ranges from 100 per cent on Day 1 of infection to 67 per cent on Day 4.
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On the day that someone starts to show symptoms of COVID-19, the median false-negative rate decreased to 38 per cent, researchers found.
In Canada, there are currently three ways to test for the virus that causes COVID-19, Health Canada says.
For people with suspected current cases of COVID-19, they will receive either a molecular PCR test — which takes swabs from the nose or throat to send to a lab for testing — or a point-of-care test, which also uses swabs but results are delivered on the spot.
Antibody tests involve blood samples and are used to see who may have already had the virus.
While testing is helpful, Phillips said, you can even have symptoms of COVID-19 and still test negative. In these false-negative situations where someone appears to have the markers of the coronavirus, health-care providers will often test again a few days later to ensure better accuracy. Self-isolation for 14 days is still recommended for anyone who has symptoms of COVID-19 or has been exposed to the coronavirus.
“The (test) sensitivity is only around 60 to 70 per cent,” Phillips said of PCR testing.
“The negative test is something that people need to be cautious about because it can give misleading, false sense of security.”
Using test results to determine socializing is dangerous
Experts want to make this clear: a negative coronavirus test is not a reason to abandon public health guidelines or rules in your region. We are still in a pandemic, and things like physical distancing, handwashing, wearing a mask indoors and keeping to your bubble is important.
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A negative test is not an excuse to engage in “higher risk” behaviour, Mertz said. There’s also no way to be certain others, like friends or members of the public, are negative for the coronavirus, either.
“Your behaviour should first and foremost be triggered by the current COVID-19 situation in the region you’re living, which will determine your individual risk rate,” Mertz said.
“The recommendation still is to follow all the rules that are out there… regardless of whether you do a test or not.”
You can be asymptomatic and spread the virus
It’s important to remember that you could be a carrier of the coronavirus and not show symptoms ever. Asymptomatic people can spread COVID-19, even if they never show symptoms of the disease themselves.
There’s a difference between asymptomatic carriers and pre-symptomatic carriers, Mertz said, as pre-symptomatic means someone doesn’t have symptoms — yet.
There are also some people who will only present mild symptoms of COVID-19, which are categorized as “paucisymptomatic,” Dr. Isaac Bogoch, an infectious diseases specialist at Toronto General Hospital, previously told Global News.
We have to take precautions against asymptomatic or pre-symptomatic transmission, experts say.
Bogoch believes that even people who only have mild symptoms, like a cough, should still get tested so that if they do have the disease, they can take appropriate isolation measures.
“With public education and with ensuring access to diagnostic testing, we can probably more readily identify people with mild symptoms in the community,” he said.
“And we can further prevent community transmission.”
Questions about COVID-19? Here are some things you need to know:
Symptoms can include fever, cough and difficulty breathing — very similar to a cold or flu. Some people can develop a more severe illness. People most at risk of this include older adults and people with severe chronic medical conditions like heart, lung or kidney disease. If you develop symptoms, contact public health authorities.
To prevent the virus from spreading, experts recommend frequent handwashing and coughing into your sleeve. They also recommend minimizing contact with others, staying home as much as possible and maintaining a distance of two metres from other people if you go out. In situations where you can’t keep a safe distance from others, public health officials recommend the use of a non-medical face mask or covering to prevent spreading the respiratory droplets that can carry the virus.
For full COVID-19 coverage from Global News, click here.
— With files from Global News’ Leslie Young
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