With hundreds of students dismissed over COVID-19 exposures so far this year in Windsor-Essex — and three school shutdowns — the acting medical officer of health says he's considering all options to manage COVID-19, but says rapid testing in schools is only appropriate in some situations.
Dr. Shanker Nesathurai, acting medical officer of health, said he has not made any "firm decisions" regarding a new rapid antigen testing program announced by the Ontario government this week.
"Testing, especially testing of asymptomatic people, has a very limited role in the management of the pandemic," he told reporters in a virtual briefing on Wednesday.
Screening asymptomatic people is likely to result in false positives, he said, which can be "a significant problem from a public health point of view."
The screening program was announced by Chief Medical Officer of Health Dr. Kieran Moore on Tuesday.
Moore called the tests "another tool in the tool chest" when it comes to curbing school-related cases and outbreaks and keeping students in class. Local public health units will have discretion in requesting the tests, he said.
Under the program, tests will only be provided on an optional basis to unvaccinated, asymptomatic children who are not considered high-risk contacts of a positive COVID-19 case, Moore said. In Ontario, children 11 and under are not yet eligible to be vaccinated against the novel coronavirus.
Those who test positive will need to undergo lab-based, polymerase chain reaction (PCR) testing and isolate until the results of the second, more accurate test is known, Moore said.
'Very limited role'
Nesathurai believes there's a "very limited role" for rapid antigen testing. It would not be "the preferred option" in the management of many school outbreaks, but it could be useful in some scenarios, he said.
"The bottom line is that you have to make a judgment in an outbreak based on the facts and circumstances," he said.
"That includes the background prevalence of the disease in the community, what one anticipates the presence of illness in that local school [will be] and the technical capacities of the different testing strategies, and putting that together we try to find a plan."
Nesathurai said he might be inclined to choose PCR testing as opposed to rapid tests.
Cynthia Carr, an epidemiologist and founder at Epi Research Inc. in Winnipeg, agreed and said because the tests are intended for low risk, asymptomatic children, rapid tests may not be the best option.
Another part of the problem is that rapid tests are less sensitive than PCR tests, meaning they are less likely to detect a positive case.
"The specific parameters might even make this testing less useful because again, you have to be shedding enough of the virus for these rapid tests to detect it," Carr said.
"I would be more inclined to do something like pooled testing using the gold standard PCR."
Carr explained that pool testing involves taking multiple samples and testing them together. If the results come back positive, the samples are tested individually.
"Rapid testing really isn't meant to be kind of a one and done situation, so it might be better if you're looking at an outbreak situation to take a sample from all of the students, for example, but then group them and do pooled PCR testing to see if you get any positive results right then and there," she said.
"It has much more sensitivity to quickly identify if somebody is infected and to be able to react to that."
New school closure announced
Nesathurai made the comments on the same day the closure of another school, École élémentaire Louise-Charron, took effect. Less than a month into the school year, three schools have been closed so far due to COVID-19, though one has since reopened.
According to local public health officials, more than 200 school cohorts have been sent home since in-person learning resumed in September. There are five ongoing school outbreaks.
Currently, there are three active COVID-19 cases within the English Catholic school board and 23 within the public board.
The health unit is encouraging anyone who is eligible to get vaccinated, including youth.
As of Wednesday, 73.2 per cent of those aged 12 to 17 in Windsor-Essex have gotten at least one dose, while the provincial figure is 81.4 per cent.