Early in October, Health Canada approved three rapid antigen detection tests (RADTs) for use in Canada to detect SARS-CoV-2. These rapidly developing technologies will change how we protect the health of workers in the next phase of COVID-19.
Rapid antigen testing detects specific proteins found on the surface of the virus. It differs from standard laboratory-based testing, which uses polymerase chain reaction (PCR) techniques that amplify small segments of genetic material in the virus. PCR tests require a health professional to collect a nasopharyngeal swab that is then sent to an accredited laboratory for processing.
Some jurisdictions in Canada are facing limitations in their PCR testing capacity. Most estimates suggest that the maximum number of PCR tests that can be administered and processed per day in Canada ranges from 80,000 to 90,000—less than half the optimal 200,000 tests per day recommended by the federal government.
These limitations result in uneven reporting of tests results. For example, the Toronto Public Health currently processes about 40 per cent of tests within 24 hours, relative to its goal of 60 per cent. These limitations have also led Ontario to restrict access to PCR testing to people who are exhibiting symptoms of COVID-19 infection or asymptomatic people who live or work in specific settings.
Here’s where rapid antigen detection tests (RADT) will be important in the next phase of our response to this virus. Rapid antigen tests do not require administration by a health-care professional, can be administered at virtually any location (including workplaces), will typically provide an immediate test result (in 15-20 minutes), do not require laboratory processing facilities and have a much lower per-test cost (as low as $5.00). Some have likened COVID-19 rapid antigen tests to the convenience of over-the-counter pregnancy tests.
The federal government has contracted to procure enough test devices and materials to administer 200,000 rapid antigen tests per day for the remainder of 2020, and anticipates additional procurement in the months ahead. This federal procurement will triple the national capacity to provide COVID-19 testing.
What’s the catch? There are two concerns. First, RADTS may not be as accurate as laboratory PCR testing. RADTs generate more false negatives than PCR tests. (A false negative occurs when a test fails to identify an actual COVID-19 infection and incorrectly delivers a negative result.) Out of 100 COVID-19 infections detected by a PCR test, a typical RADT will miss about seven of these. However, our understanding of the performance of RADT is improving rapidly. Increasing evidence indicates that RADTs and PCR tests are equally accurate in the detection of infections among asymptomatic people in the first five to six days following infection onset, when viral loads are highest and the risk of person-to-person transmission is greatest.
The second concern is the complicated challenge of integrating the administration of workplace-based rapid antigen testing into public health surveillance programs. Dr. David Naylor, a leader of Canada’s COVID-19 Immunity Taskforce, notes that antigen tests will have a place in screening for infection: “More rapid on-site testing strategies will be a game-changer... What we’re talking about are rapid tests that can be done on-the-spot for screening of asymptomatic people in contexts like schools or worksites with a view to getting results in minutes, not hours or days.” Positive RADT results in a worker would be a priority for confirmation by laboratory PCR and for initiating contact tracing within both the workplace and the community.
What might we see in the near future as rapid antigen testing is used to monitor COVID-19 infections in Ontario workplaces? Health Canada has offered some initial tentative perspectives on the use of RADTs for the monitoring of asymptomatic people in high-risk settings, suggesting priorities could include the repeated testing of workers in remote work areas to prevent the introduction or minimize the spread of infection, repeated testing of inmates and workers in correctional facilities, and regular testing of workers in high-risk settings such as long-term care facilities and large food processing facilities.
Following the Health Canada licensing of RADT products, Canadian airline company Air Canada has ordered 25,000 coronavirus testing kits to be administered to employee volunteers. Other large employers in critical infrastructure sectors may also independently procure RADTs to assure employees and customers/clients.
Rapid antigen tests may also be used in other settings that may help reduce worker exposure, such as schools and urban transit systems. And we might anticipate an important use of RADTs in quickly evaluating the infection status of workers in workplaces where public health officials or occupational health and safety regulators suspect COVID-19 transmission.
The use of RADTs in the workplace gives rise to important questions. Who administers tests in the workplace? Which workers get them? Who gets the results? How are the results used? How are results integrated into the public health surveillance system? With due consideration of these issues by policy-makers and workplace parties, rapid antigen testing may be key in rebuilding the economy while keeping workers safe.
— Dr. Cameron Mustard, President and Senior Scientist, Institute for Work & Health