RAPID ANTIGEN TESTING WORTHY OF MORE USE
Frequency of use for testing kits needs to be aggressive, Peter W.B. Phillips says.
Governments everywhere seem to have run out of strategies for managing the COVID-19 pandemic. Doubling down on shelter-in-place policies are a tacit admission that all our public health measures — surveillance, quarantine for travellers, isolation for infected individuals, mass testing, vaccination, and hospitalization — are not up to the task. So is that it?
I believe there is at least one tool on the shelf that we have not yet used fully: Antigen testing for use at point-of-care. We were quite enthusiastic about this approach back in the fall. Health Canada in October to December approved six different tests from three companies and the federal government contracted for 38 million rapid test kits. At least 3.8 million are in Canada and in the last few weeks they have begun to be distributed to provinces, but so far, few have been deployed.
A few pilot studies have been tried at airports, bars and some workplaces but general uptake has stalled. Only on Thursday did the Saskatchewan government announce plans to expand rapid testing using 700,000 kits.
Currently, we use nucleic acid technology lab-based test, which involves drawing a sample from the back of your throat with a swab and sending it for genetic analysis in a laboratory. These tests detect almost all infected individuals and are vital parts of our clinical treatment of COVID-19. The problem is the laboratory analysis takes about six hours and, with the transport and logistics of getting the samples to the labs, most people are only hearing results at best 24 to 48 hours after the sample is taken. In that time, they could be infecting others. Clearly, these tests are not fast enough to help in managing the disease in our daily affairs.
We need to actively test where the diseases are incubating. Our testing protocols for the most part seem to rely on individuals to self-identify for testing. Asymptomatic individuals and those with minor symptoms remain socially active and add to the growth in cases.
This is where rapid tests fit. When Health Canada regulators evaluated and approved these tests, they judged that they were anywhere from 83.2 per cent to 96.7 per cent effective, delivering results at the point-of-care in as little as 15 minutes. The problem is that recent field testing suggests that they may be far less effective than that. The U.S. Centres for Disease Control reported on a study of a test population of 1,098 people, nucleic acid labbased tests identified 54 people with infections while the rapid antigen test detected only 38 of these people (many with one or more symptom). The antigen test failed to detect 16 people who were infected (most who were asymptomatic) and also falsely detected 18 people as infected who weren't. That is about a 70 per cent success rate. When the test results for the asymptomatic population were isolated, the rate of successful detection of infected people dropped to just over 40 per cent. As a one-time test, that isn't overly impressive and few places are using the test.
These tests, if used more intensively, could go a long way to managing the virus. All the testing was done only once. If 70 per cent effective tests were administered to an isolated group of people not once but daily for an extended period, and all positives (correct or false) were isolated, the test would detect all the infected people within four days. If we take the worst-case scenario and assume only about 40 per cent success, within 10 days all infected individuals would be detected.
Obviously, this is simple math on a static population. The virus actually is more dynamic. Over time, the viral load for infected individuals would increase daily, making detection easier, which suggests this might be a worst-case scenario. Offsetting that, people would be getting infected outside these settings, so there would be a sustained flow of new infection. Simulations suggest that repeated antigen testing could control infections in a workplace or long-term care facility to the rate of infections introduced from outside the group. The spread of the virus inside these settings would effectively be halted.
So even a weak test can add to our tool kit. If implemented aggressively in high density places, such as larger workplaces, long-term care and seniors homes, schools and larger retail outlets (where Ontario reports more than 60 per cent of infections are emerging), we would go a long way to identifying infected individuals that could then be isolated and treated, breaking the infection chain more effectively than our current system.
Lowering the overall infection and reproduction rate in workplaces and care homes, would help to lower mortality, minimize the costs of infections and reduce losses from economic disruption. This is a win-win-win strategy, especially when we realize that we actually have bought and paid for these tests and they are already in Canada and available for use.
Lowering the overall infection and reproduction rate in workplaces and care homes, would help to lower mortality (and) minimize the costs of infections …