Users of rapid antigen detection tests for COVID-19 make several errors when handling them and when interpreting the results, Montreal researchers have found, but the situation can be remedied by providing them with instructions more detailed.
Some of the most common errors involved the amount of liquid that should be used and the identification of a positive result, especially when the line which testifies to the presence of the virus is particularly faint, specified doctor Cédric Yansouni, of the Research Institute of the McGill University Health Centre. Doctor Yansouni recalls that several countries hastened to deploy these self-tests during the pandemic without having first checked whether users were able to use them and interpret them correctly. “There was a need to determine how much we can trust the performance of people who do their own test, and that’s what we tried to do,” explained Dr. Yansouni.
A team visited businesses where at least two active cases of COVID-19 were identified by Montreal Public Health. The team visited each company twice a week for two weeks. At each visit, study staff instructed participants in the procedures for taking nasal swabs and provided them with either the manufacturer’s guide or a modified quick reference guide, without providing further details. In total, 1892 tests were carried out on 647 participants.
At the first self-diagnostic visit, 55.6% of participants who received the modified guide correctly identified a weak positive test result, compared to 12.3% of participants who used the manufacturer’s guide. Similarly, for a positive result, the correct identification rate increased from 51.5% with the use of the manufacturer’s guide to 89.6% with the use of the modified guide. Improvements were also seen with a strong positive result and with an invalid result. “In the amended instructions, there was a lot of emphasis on interpretation, so not just showing one example of a positive and one example of a negative,” Yansouni said.
“We invited people to systematically ask themselves, ‘Is the test valid? Is the test negative? Is the test positive? Here are examples of barely visible lines which, despite this, are absolutely positive’. And then when we deployed that among different untrained people, we saw a dramatic difference. With an extremely simple intervention, he adds, “we were able to improve the interpretation of the majority of the positive results. With simple intervention, untrained people achieve a level of reliability that (approaches) that of a professional”.
The researchers did not try to find out what caused the users of the self-tests to interpret the results incorrectly, for example in the presence of a faint line which indicates a positive result. However, Doctor Yansouni reminds us that the human eye is not infallible. There could also be a psychological component to the phenomenon.
“The first step, he said, is to know the extent of the reading bias that is introduced when doing tests at home, because I do not believe that rapid tests for COVID will be the last tests we use. The biggest challenge for the authorities is not only to deploy them, but to find the right way to communicate with the public the correct interpretation of the test which will change according to the epidemiological situation. And that is not easy. »
At the time of the study, the rapid tests were not yet approved by Health Canada for self-use by untrained individuals. The vaccine was just beginning to roll out and there were multiple outbreaks in the workplace. The results of this study were published by the medical journal JAMA Network Open.
Crédit photo: THE CANADIAN PRESS/Jeff McIntosh.