Experts warn of negative coronavirus test as free pass to group socialization


TORONTO – When Bonita Mak went to visit a friend at a country house outside of Toronto, she says she had a COVID-19 test beforehand to make sure she wasn’t putting people on around her in danger.The 25-year-old lived through a social bubble, but decided to take a test before meeting another friend and relatives as the best way to safely escape her city apartment after months of lockdown .

“I wanted to make sure I wasn’t asymptomatic and get him out,” Mak said. “It seems like the best precaution to take.”

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But while the COVID-19 test is readily available in Ontario, experts warn of their shortcomings. They say the tests cannot detect the virus during its incubation period and still produces a considerable rate of false negatives.

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“People can have a false sense of security with diagnostic tests,” said Dr. Isaac Bogoch, an infectious disease specialist. “The diagnostic test is only useful for a short period of time and doesn’t really tell the whole story.”

Bogoch pointed out that there is an incubation period of four or five days after exposure during which the coronavirus is in your body but cannot be detected. It is possible for a person to test negative during the incubation period and then become contagious for up to 14 days later when symptoms appear, he said.

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Colin Furness, an infection control epidemiologist at the University of Toronto, said the test was about 65% accurate. False negatives can occur if a patient has only recently caught the virus and has not multiplied enough to be caught by the nasal swab.

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The swab test could also be done incorrectly or be missed during handling in the lab, he said.

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“The technology is solid, but you don’t really have high precision, not really the kind of precision you think of when you think of this type of testing,” Furness said. “There are a lot of opportunities to get negative tests and expose other people because you are infected and there has been a problem with the test.”

Furness said the test was uncomfortable and people could just tell they had been tested when they weren’t. He likened the script to trusting a partner who says they don’t have a sexually transmitted disease.

“You transfer what is a scientific measurement to a matter of taking someone at their word,” Furness said.

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On Monday, Dr. Eileen de Villa, Toronto’s chief medical officer of health, said she understood people wanted to get back to normal lives, but testing was not a good way to do it.

“We have to recognize that a test is flawed – it tells you what your situation is like at a given time,” de Villa said. “I appreciate that people want to connect, but the more we are able to follow the advice of the public, the sooner we can resume these regular activities.”

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De Villa’s comments came as Health Minister Christine Elliott pointed out that more than 50% of new coronavirus cases in Ontario were in people 39 years old and under, which she called a worrying trend.

But Mak said many young people around her take tests before entering social situations. She said she would do this again before going on an extended trip with the elderly, but that she does her best to limit her interactions with others.

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© 2020 The Canadian Press


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