TORONTO – As provinces rely more heavily on rapid antigen testing as part of a strategy to limit the spread of COVID-19, there have been concerns about the possibility of false-positive results. Canadian researchers have produced new data that sheds light on the possibility of such events.
Researchers from the University of Toronto’s Rotman School of Management published their peer-reviewed findings in the journal JAMA earlier this month. They looked at the results of more than 900,000 rapid antigen tests performed in 537 Canadian workplaces between January and October 2021.
During this period, Canada had two significant waves of COVID-19 driven by the Delta variant. A total of 1,322 positive results were recorded using the rapid tests. Of these cases, 1,103 also had data from the PCR test to compare with.
In total, 462 rapid test results, 0.05% of the 900,000 results, gave false positives. This number represents 42% of the positive test results in the study.
The tests performed too late in infection or improperly are some of the possible reasons for these false negatives, the researchers said.
About 60% of these false positives can also be traced back to problems with a single manufacturer. There were 278 false positives from two workplaces, all drawn from a single bad batch.
“The overall rate of false-positive results among the total rapid antigen screening screens for SARS-CoV-2 is very low, consistent with other smaller studies,” the researchers wrote. writing research. “These results inform the discussion about whether rapid antigen tests lead to too many false positives that could overwhelm the capacity for PCR testing in other settings.
The authors also say their findings illustrate the importance of “a comprehensive data set” to quickly identify bad batches of rapid tests.
“With the ability to identify batch problems within 24 hours, workers can return to work, problematic test batches can be eliminated, and public health authorities and manufacturers can can be informed,” they wrote.