Is more testing behind the record numbers of COVID-19 cases in Canada? Your testing questions answered
Also, are pharmacy tests accurate? Why am I still testing positive weeks after recovery?
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We're answering your questions about the pandemic. Send yours to COVID@cbc.ca, and we'll answer as many as we can. We publish a selection of answers online and also put some questions to the experts during The National and on CBC News Network. So far, we've received more than 55,000 emails from all corners of the country.
COVID-19 testing is a crucial part of tracking and managing the pandemic. It has become a part of daily life that's often necessary for returning to work or school or for keeping friends and family safe.
But it also generates a lot of confusing news and advice from case counts to wait times to ever-changing instructions about who needs to get tested, when, how and why.
It's no wonder CBC readers have lots of questions. We checked with experts to get some of the answers.
Is the present spike in COVID-19 cases in Canada related to the increase in testing?
Many provinces have been breaking daily new case records for COVID-19, including British Columbia, Alberta, Saskatchewan, Manitoba, Ontario, and Quebec. But these provinces are all running more tests now than they were at the previous peak in the spring when a shortage of tests meant even people with very typical COVID-19 symptoms couldn't get tested. So, are the increased case counts simply due to more testing? For the most part, no. But the amount of testing does make a difference.
For Ontario, the new records are partly due to the increase in testing, said Dr. Sumon Chakrabarti, an infectious disease specialist with Trillium Health Partners in Mississauga, Ont., in an interview with CBC News Network.
Ontario completed over 48,000 tests on Oct. 7 (two days before setting a record of 949 cases in one day) — about quadruple the 12,000 it ran on April 24 when the province hit a spring peak of 640 cases.
At that time, Chakrabarti estimates about three-quarters of cases were being missed, and there were likely closer to 2,500 cases a day in late April.
However, the real number of cases in Canada is definitely higher than it's been since the spring peak.
All things being equal, if you test more of the population, you will end up testing more people with COVID-19, which will cause the case counts to go up, but you will typically test even more people without COVID-19, causing the percentage of positive tests to decrease, said Cynthia Carr, founder of the Winnipeg-based epidemiology consulting firm EPI Research Inc.
But in fact, the percentage of tests that come back positive is increasing in many places, including Manitoba. In that province, the real number of cases is "definitely an increase relative to the spring."
Ottawa wastewater surveillance shows dip in COVID cases. The timing is too perfect. 2 weeks after new restrictions we're seeing this strong a signal? Other explanations out there? I'm all ears. <a href="https://t.co/VY9J53Lj5k">pic.twitter.com/VY9J53Lj5k</a>—@deonandan
And in Ottawa, SARS-CoV-2 virus levels in waste water in recent weeks are the highest they've been since testing began in June. That's a measure of COVID-19 prevalence independent of the amount of testing at testing centres, said Raywat Deonandan, an associate professor of epidemiology at the University of Ottawa.
The good news? Coronavirus levels in waste water seem to be going down since the province imposed stricter restrictions on social gatherings in the city before Thanksgiving.
WATCH | How sewage can be used to track COVID-19:
If we can test feces in waste water for coronavirus, why are we still doing invasive nasal swabs?
Having your nose swabbed can feel really uncomfortable, but Dr. Matthew Cheng, an assistant professor of medicine at McGill University, said there are practical reasons for it:
Public health doctors are more interested in knowing if the virus is in the respiratory tract, which the nose is part of, as it's mainly spread via the respiratory tract.
Lab protocols are optimized to process lots of respiratory samples and having other kinds of samples could slow down analysis.
He said that there's lots of work underway to be able to quickly analyze respiratory tract samples that are easy for people to collect themselves, such as "swish and gargle" saliva tests. Lastly, many people may not find collecting a stool sample easier than getting a swab in the nose.
WATCH | A closer look at saliva-based tests:
How long are test samples good for?
With backlogs in testing in Ontario this fall, at least one local health director has complained about tests spoiling and having to be redone after they weren't processed within 72 hours. Dr. Robert Cushman, acting medical director of Renfrew County and District Health Unit in Ontario, reported that the testing lab told him that about 10 tests had to be redone due to delays in processing.
So how long do they last?
It depends on how the swab is stored after collection, said Allison McGeer, an infectious disease specialist at Toronto's Mount Sinai Hospital, but generally speaking, it should last weeks.
Benoît Hébert, a Quebec-based biotechnology consultant, said most biological samples including nasopharyngeal swabs can be stored at regular fridge temperatures for up to 72 hours and should be deep frozen if there is any delay in testing or shipping.
According to Public Health Ontario, tests have about a 95 per cent accuracy rate as long as the test is processed within seven days of collection, and the sample is taken using a nasopharyngeal swab.
As of mid-October, more than half the tests in Ontario were processed within two days, the Health Ministry told CBC News in an email. It said that accredited labs conducting testing must have equipment in place to keep specimens at a stable temperature before testing, and it recommends freezing samples to preserve them.
"In the event a laboratory would report a specimen as expired, they would contact the testing site to ensure that re-collection occurs," the ministry said.
WATCH | A closer look at rapid COVID-19 testing:
I got COVID-19 and isolated for the required time. But I'm still testing positive. What does that mean?
"Many people have these lingering positive tests," acknowledged Chakrabarti, and that can happen weeks or months after they recover. But at that point, he said, "they're not actually contagious."
Dr. Zain Chagla, medical director of infection control at St. Joseph's Healthcare in Hamilton, explained that's because COVID-19 tests detect genetic material from the virus, which can be shed from your body even when all the viruses are dead.
So how long is a COVID-19 patient contagious?
Chagla said that researchers trying to culture live virus from patients have found there are minimal amounts in most people 10 days after they experience their first symptoms and after 20 days in critically ill patients. That suggests they're not contagious after those periods.
"There's also been no case reports of people being infected by others who are 10+ days into their illness," Chagla added in an email.
It also means long-haulers, people who are still experiencing symptoms months after they got infected, are not contagious.
WATCH | Doctors take questions and give answers about COVID-19 testing:
I've recovered from COVID-19, but my boss says I need to test negative before I can return to work. Can they ask me for one?
Given that people can test positive for weeks or months after recovery and aren't contagious, a request like this may be frustrating.
But the answer is yes.
Even if you've completed isolation and public health has cleared you, employment lawyer Howard Levitt said it's within your employer's rights to require a negative test — and they're not obliged to pay you if you're unable to work.
"Safety trumps privacy. That's the bottom line," said Levitt, noting that employers could ask for a negative test result every two weeks, if they wanted to, needing no other reason than ensuring a safe workplace.
So what can workers do?
You could try talking with your boss or getting a doctor's note, said Maggie Campbell, a partner at Vancouver law firm Roper Greyell.
Other than that, Levitt says there isn't much you can do. You can offer to work from home, if possible, or you could take your employer to court, but he cautioned that courts may not be in workers' favour in the current climate.
"Employees should understand that anything an employer is doing to protect other employees of theirs will be seen very sympathetically by the courts."
However, companies should be up-to-date with the latest public health guidelines, he said.
If your employer sends you home without pay while awaiting a negative test result, you could apply for Canada Recovery Sickness Benefit, providing you are eligible.
WATCH | Labour lawyer answers questions about work during pandemic:
I have symptoms but tested negative. Do I still have to self-isolate?
It's always best to check with your health-care provider or local public health unit for advice specific to your personal situation. But symptomatic individuals may be advised to continue isolating for the remainder of the isolation period, even if they get a negative result.
That's because a negative result isn't a guarantee that you don't have the virus.
According to Dr. Kelly MacDonald, head of the infectious disease program at the University of Manitoba, the nasal swab test is accurate 99 per cent of the time in a laboratory setting, but in a clinical setting errors can happen when the sample is taken. For example, the swabbing may not be done properly.
A negative test could also mean that you were tested too early before viral levels are high enough to be reliably measured.
Ultimately, context is important, and your doctor or local health unit would form their advice on a number of factors, including whether there was exposure to a known case, the kind of symptoms you have, how long you've had them and whether you're a student, or you work with vulnerable individuals, for example.
And even if you don't have COVID-19, you could still be contagious with something else — perhaps the flu — in which case, the same public health advice to stay home when sick would still apply.
On the other hand, if you get a positive test, you almost certainly have COVID-19 — the false positive rate is very low — less than one per cent of tests overall, estimates Dr. Philippe Lagacé-Wiens, a medical microbiologist at St. Boniface Hospital in Winnipeg.
WATCH | Why people with COVID-19 symptoms should be reassessed if they test negative:
If you're a contact of someone who tested positive, why are you supposed to get tested within 2 weeks of exposure? Wouldn't the virus still be developing?
While it can take up to 14 days for symptoms to develop, Charkrabarti said that most people start to develop symptoms within seven days.
"And you can actually test positive a couple of days before that," he said.
So ideally, you should wait about three to four days after exposure before getting tested, he recommends.
However, any result could still be a false negative, so if you were exposed, you should remain in quarantine for 14 days even if you test negative.
Are tests at pharmacies as accurate as those at provincial testing centres?
In general, people with no symptoms are more likely to get a false negative than those with symptoms, but it's not known by how much.
In Alberta, the tests are identical to those offered at provincial testing sites and analyzed at the same labs, the provincial Health Ministry says. That means they should have similar accuracy to tests of asymptomatic people at testing centres. However, Alberta announced on Oct. 20 that it would stop testing asymptomatic people with no known exposure to COVID-19 — the only people who could get tested in pharmacies.
In Ontario, there are some differences between pharmacy tests and those offered at provincial testing centres. Pharmacy tests use shorter nasal swabs instead of the long nasopharyngeal swabs, and they're sent to the California lab of Quest Diagnostics instead of in-province labs, says the provincial Health Ministry.
Chagla says the sensitivity may be slightly lower with the shorter swabs, but this shouldn't be a big risk, as the probability of asymptomatic people having COVID-19 is lower than people with symptoms, especially if they haven't been exposed.
WATCH | How pharmacy testing works in Ontario:
I think I had COVID-19, but I'm better now. Can I be tested to confirm?
The nose swabs at testing centres can only detect current or very recent infections, not whether you've been previously infected. To find that out, you need an antibody test. Such tests are available 14 days after active infection, with a doctor's prescription, in some provinces. Dynacare offers the service in Ontario and Quebec. Ichor Blood Services offers it in some communities in Alberta, Ontario and New Brunswick. The fee is typically $70 to $80.
However, studies have shown that even among those infected, antibodies fade with time, and it happens far more quickly in those who never showed symptoms.
WATCH | A closer look at the 1st antibody test Health Canada approved in May: