MONTREAL -- Rapid tests for COVID-19 that are being rolled out in Quebec schools could at least help avoid sending children with worrisome symptoms home unnecessarily, a new Quebec study shows.

The Ministry of Health and Social Services and the Ministry of Education recently announced that the tests would be implemented in schools in 10 regions of the province, including Montreal, Laval and Montérégie.

Dr. Caroline Quach-Thanh, from the CHU Sainte-Justine, and her colleagues studied the optimal use of rapid tests to contain outbreaks and evaluated their effectiveness in schools.

They concluded that polymerase chain reaction (PCR) testing remains the most sensitive technique in symptomatic individuals, but that rapid tests have a role to play when children are symptomatic.

"If you come in in the morning and realize the child has a little cough and maybe a sore throat, if the test is negative, the child can stay in school," said Quach. "Obviously, if it persists, we would have to go and do a PCR (test) as usual, but we are able to allow school attendance around that test."

Rapid tests may miss some SARS-CoV-2 infections compared to PCR tests, but the risk is lower in patients who are symptomatic. These rapid tests are also more effective when the viral load is high, which is when the contagion is greatest.

Quach concluded that rapid tests should be reserved for symptomatic people first.

While the tests may allow some children to stay in school or daycare, she said, discretion will still be required, since the criteria that existed prior to COVID for sending a child home remain valid.

"If the child has a fever, is not well, is not able to follow activities, they should still be sent home," she said. "If he has a fever of 39 and the test is negative, he's amorphous, he's not able to follow what's going on in class, there may be influenza, there may be other viruses that we don't want to pass on either."

The study results were obtained through the participation of more than 2,000 high school students and nearly 300 school staff members recruited from two Montreal high schools and followed between January and June 2021.

The researchers found a higher proportion of asymptomatic cases in these participating schools, which would mean that more cases were missed in other schools in the province.

In addition, of the infections for which the source was known, 72.5 per cent were from family transmission and 25 per cent were from school transmission.

-- This report by The Canadian Press was first published in French on Oct. 18, 2021.