What's up with the false negative test results? Your COVID-19 questions answered | CBC News

2022-09-24 03:17:54 By : Mr. David Hu

The information in this article was current at the time of publishing, but guidelines and advice can change quickly. Check with your local public health unit for the most-current guidance, and find the latest COVID-19 news on our website.

We're breaking down what you need to know about the pandemic by answering your questions. You can send us your questions via email at COVID@cbc.ca and we'll answer as many as we can. We'll publish a selection of answers every weekday on our website, and we're also putting some of your questions to the experts on the air during The National and on CBC News Network. 

We've received tens of thousands of emails from all corners of the country. Your questions have surprised us, stumped us and got us thinking, including a number of questions about properly washing your produce and false negative test results. 

We continue to get a lot of questions about testing, including emails from Catherine and Michael H., who are wondering whether false negatives can be blamed on faulty nasal swabs?

Nasopharyngeal swabs go through the nose first, and then are rotated at the back of the throat to collect viral specimens. The procedure can be uncomfortable. 

Microbiologist Craig Jenne tells CBC News that false negatives can be blamed on non-cooperative patients or on somebody who has never done a nasal swab before. In other cases, a throat swab may not reach the virus.

Dr. Christopher Labos, an epidemiologist and cardiologist in Montreal, believes timing is a bigger factor.

"There's some evidence now to suggest that if you were only tested three to four days or a week after your symptoms start, your levels are going to be lower," he said, which makes it harder for the virus to show up on a test.

"We are probably underreporting cases a little bit," said Labos.

According to Craig Jenne, associate professor in the department of microbiology, immunology and infectious diseases at the University of Calgary, "We can't guarantee that the test is going to catch 100 per cent of the infected people so we're using it really as a confirmation of people with symptoms."

We get a lot of emails, including from Steve F., who want to know how to clean produce.

Jeff Farber, a food science professor at the University of Guelph says you should not wash fruits or veggies with soap, which is known"to cause vomiting and/or diarrhea." So skip the soap, and wash raw fruits and vegetables thoroughly in cold water. 

Dr. Siyun Wang, a food safety and engineering associate professor at UBC, says produce is just as safe as before the pandemic, because the latest science suggests "the coronavirus is not transmitted through food." 

Wang reminds everyone to wash their hands when they get home from the grocery store, before handling food.

There have been no reported cases of "COVID-19 transmission through food," according to the Canadian Food Inspection Agency. 

You can read more about Health Canada's produce safety cleaning tips here.

This isn't the first time we've tackled questions about pets and the coronavirus, but because the information is changing all the time, we decided to revisit this topic and answer an email from Mark M.

Initially, the World Health Organization (WHO) suggested there was no evidence pets could be infected with the virus, after reviewing the COVID-19 canine case in Hong Kong.

But now, the WHO says it is "aware of instances of animals and pets of COVID-19 patients being infected with the disease."

What changed? We now know there are confirmed reports of animals being infected with the coronavirus, including a tiger in the U.S.

"We've always had the assumption that animals could be infected because it came from an animal," said Dr. Scott Weese, a veterinary professor at the University of Guelph who researches emerging infectious diseases and infection control. 

However, he adds that not all animals are susceptible to the virus to the same degree. Cats and ferrets seem to be the most vulnerable, but dogs don't face "too big of a risk."

As far as entering the food chain, Weese says "it doesn't seem to be too much of a concern" after two tests suggested no sign of the virus in pigs. 

"They [experimental tests] have been small but they were able to check pigs so that's a good sign."

And while the virus did originate in animals, it has now largely become a human virus.

"Basically, this is a human virus now, and it occasionally can spill over into animals," said Weese. "But they have to have direct contact with a person to get it."

We have been getting a lot of questions from many of you who have been unable to get a full night's sleep. 

Major events like this pandemic can lead to insomnia, sleep experts say. 

"Everyone's routine is being disrupted. It's a severely stressful event," said Dr. Atul Khullar, an Edmonton psychiatrist and senior consultant for MedSleep, a group of sleep clinics.

This provokes anxiety and stress, exacerbating any pre-existing mental health and insomnia problems, or causing new ones, he said.

It turns out that disrupted sleep in times of crisis has deep roots, according to evolutionary anthropologist David Samson, an assistant professor at the University of Toronto who studies the evolutionary links between sleep and cognition.

Sleeplessness is in part a fear-related survival technique connected to how we evolved, he said. We had to be alert to life-threatening forces like predatory animals and severe weather, say, 1.5 million years ago. But we also lived in groups where people could take turns keeping watch at night.

"It turns out fear is actually a good thing from an evolutionary perspective," said Samson. The problem is our psyches stay on high alert when we sense threat.

Because we can't just chase off this problem, we are unable to extinguish our fear, he said. "It's turning into what we classically call insomnia, which is a perpetual chronic condition characterized by the inability to fall asleep." 

But since sleep is critical to both emotional regulation and immune strength, Samson said it's worth your while to establish good sleep habits, like turning off screens an hour before bed and sticking to consistent sleep and wake times.

Read more tips for sleeping easier in this uncertain time here.

WATCH | We're also answering your questions every night on The National. Last night, you asked if help was coming for renters or people with reduced incomes:

Tuesday we answered questions about disinfecting with ultraviolet light and possible virus transmission through the ears. 

Keep your questions coming by emailing us at COVID@cbc.ca.

With files from Michelle Song and Susan Treen

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