What a negative Covid home test result means

When Dr. Jillian Horton, an internal medicine physician in Winnipeg, started feeling ill, she was pretty sure she had Covid. Her husband had been exposed and was also showing symptoms. She decided to conduct a one-time experiment, testing herself multiple times over the course of a few days to track the dynamics of the virus. “With my husband testing positive and myself very symptomatic, I was sure I had Covid,” Dr Horton said. “I was curious to see what I could determine in terms of when I could turn positive.”

Dr Horton’s husband fell ill on a Friday night and that night she tested negative. On Saturday, she started feeling sick and tested herself three times during the day. All three results were negative.

On Sunday morning, she woke up and felt worse. At 6am she tested and saw a faint line on the test – what she called a “weak positive”. She took two more tests on Sunday and both came back negative.

On Monday morning, she tested again and the test quickly came back positive.

What’s remarkable about Dr. Horton’s experience is that if she had taken the test at a different time on Sunday, she might never have discovered the weak positive. His immune system was clearly battling the virus, as evidenced by his two negative test results later that day.

Dr Horton noted that testing at the right time to catch a high viral load was similar to putting a mosquito net in a stream. If the fish isn’t there, you won’t catch anything. But if you time it so the fish are plentiful, you’ll catch your dinner.

Dr Horton said she was worried too many people would think the tests don’t work when in fact they are a useful tool if you understand how to use them. They are ideal for “governing” Covid, but there is more information you need to consider when evaluating a negative test.

“So often I hear people say, ‘The test is useless,'” Dr Horton said. “What my experience has illustrated is that when you have symptoms, testing is really rule testing. I think of those two days when I was so symptomatic. I had one positive test and five negative tests. There was only one moment in there when I was more contagious.

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