covid-19 test types and what we can count on
4 minute read
lines for nasopharyngeal swabs have become getting longer in canada. more accessible tests should ease bottlenecks.
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with children back in school, the number of covid-19 cases is steadily on the rise once again. wait times at testing sites are also up, some taking as long as six hours.
with testing still the only way to confirm whether or not you have covid-19, public health experts are calling for more options to ease bottlenecks and increase accessibility.
“having to actually go to an assessment centre is part of the challenge if you want people to get tested,” says ashleigh tuite, an infectious disease epidemiologist and professor at the university of toronto.
“first, you physically have to get there, which can be challenging for people who don’t have a car or are not near an assessment centre. if you’re not feeling well, you’re not going to want to ride on public transit.”
tuite also points to lengthy lineups as a deterrent to seeking testing.
“even if you’re able to get to a testing centre, you may not want to wait for four hours,” she says. “the weather, now at least, is nice, but once it’s freezing cold outside, the prospect of standing outside for hours waiting for a test is not very appealing and it’s going to result in people not going — particularly if they’re not feeling well.”
there are currently three tests available, and pending, for covid-19.
the gold standard: pcr test
most covid-19 tests detect the virus’ rna with a technique called polymerase chain reaction (pcr). patient samples are sent to a lab that looks for the novel coronavirus’ genetic material.
samples can be collected through a throat swab or most commonly, through a nasopharyngeal swab, which is inserted deep into the nose. because it goes relatively deeply, the sample needs to be collected at a covid-19 assessment centre by a healthcare worker.
however, yesterday, the government of british columbia announced a new, less-invasive method for school-aged children, between ages four and 19. children receive a sterile saltwater solution that they swish and gargle three times before spitting it into a tube. the tube is still sent to a lab for pcr testing. it can take hours to process, and results take at least one day.
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“the big difference is convenience. rather than having to go and get samples, anybody could collect that sample,” says tuite.
“if you were a parent, you could get a sample from your child without a healthcare worker. if you had a child who was symptomatic and in a school setting, a teacher or a public health nurse could supervise and collect the sample. so you don’t actually have to go to an assessment centre to get that sample collected.”
b.c. provincial health officer dr. bonnie henry says the saliva-based test was developed in b.c. and is the first of its kind in the world. it will be available in covid-19 collection and assessment centres across b.c.
the in-demand: rapid antigen tests
antigen tests are much faster and cheaper than pcr tests, but none have been approved in canada yet. instead of looking for the virus itself, antigen tests looks for viral proteins — or antigens — on the surface of the coronavirus.
“the easiest way to think of the antigen test is like a home pregnancy test,” says tuite. you get the results almost immediately.”
in the u.s., only one antigen test for covid-19 has been approved so far.
developed by abbott laboratories, the 15-minute test, called binaxnow, uses a test card with a test strip and a well to hold the swab. a nasal swab is taken from the patient, inserted into the well so it touches the test strip. similar to a pregnancy test, results are interpreted based on the presence or absence of pink/purple colored lines.
these tests are cheap to produce and results are determined quickly because lab processing is not required. although a health professional is needed to conduct the nose swab or saliva sample, results are nearly real-time, confirming within minutes whether there is active infection or not.
but antigen tests can be less accurate than genetic tests.
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only time will tell
until the government of canada introduces antigen tests to canadians, it’s not known if they will help ease our lagging wait times.
“the biggest unknown right now is that we haven’t tested them in canada,” says tuite. “in theory, i think they’re a great idea and would really change our response to the pandemic. but the reality is even when antigen tests become available, we still need to do [genetic] testing to understand how well they perform, if they do what we think they’ll do. you’re not going to figure that out until the test has been used in the population.”
she says antigen tests could work as a first line of defence as a confirmatory test that can indicate whether people need to wait in line for the more definitive pcr test to confirm the result.
“having a test that’s not as accurate or sensitive as the pcr test — one that can be rapidly used to identify people who are infectious, that doesn’t require going out, waiting in line, and waiting for the long turnaround to get the result — is going to help.”
“what’s the optimal way of using these tests, knowing they’re not perfect? the idea is even if it’s imperfect, if it’s wisely used and used frequently, that results in it having an impact in finding infections and reducing transmission.”
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