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The Thorncliffe Park Public School in East York on Nov 25 2020.Fred Lum/The Globe and Mail

A pro-active COVID-19 testing blitz at one of the country’s largest elementary schools has sent more than 250 children into self-isolation, raising concerns about asymptomatic spread and screening measures.

The Toronto District School Board said a voluntary testing program at Thorncliffe Park Public School has so far uncovered 19 positive cases – 18 children and one staff member – and, as a result, the school has temporarily closed 14 classes out of 42. That means there were one or two positive cases in each class, as opposed to one large cluster.

However, it is unclear if infections were transmitted in the school or in the neighbourhood, which has seen a large number of COVID-19 cases. The elementary school, northeast of the city’s downtown, is minutes away from a cluster of high-rise apartment buildings, with a large racialized population mainly from South Asian countries.

The role schools play in the spread of COVID-19 has been the subject of debate since the beginning of the pandemic. Public-health officials and provincial governments have insisted that infection-control measures, including masks and physical distancing, allow schools to remain open. But the worry among educators, doctors and infectious disease experts is that not enough testing is being done.

Janine McCready, an infectious diseases physician at Michael Garron Hospital, one of the organizations conducting the blitz, said she has pushed for testing in schools, because children generally have mild symptoms or are asymptomatic.

“If you want to keep the schools open, which is everyone’s priority, then you have to give them the best chance to not have multiple COVID introductions,” Dr. McCready said.

The Thorncliffe Park school is in a community that serves as a landing pad for immigrant families because of the availability of affordable housing. About 12 per cent of residents’ tests came back positive in the week of Nov. 15, according to ICES, a non-profit Ontario research organization formerly known as the Institute for Clinical Evaluative Sciences.

The school is part of a provincial program that is testing students and staff in areas experiencing high rates of COVID-19 infections. Ryan Bird, a spokesman for the Toronto school board, said on Monday that 270 students and 17 staff were self-isolating. The school’s enrolment is around 1,400, but this year about 650 students chose virtual school.

Dr. McCready said more than 75 per cent of students received consent from families to be tested. The 19 confirmed cases were part of a group of students and staff who were tested late last week. The remaining students were tested Monday, and results are expected this week. Dr. McCready said families of students who tested positive were encouraged to get tested, as well.

In speaking with families, she said she learned that some children had mild symptoms, which improved, and they ended up attending school. She said the health screening guidelines for schools and daycares are “too complicated.”

“In this setting, where we have uncontrolled community transmission in Toronto and the rates are just going through the roof, you really need to take a step back and simplify the screening,” Dr. McCready said.

Ontario Education Minister Stephen Lecce told reporters on Monday that about 4 per cent of tests at the school came back positive, lower than in the wider community. He did not directly answer a question about the steps his government would take to understand where transmission is occurring. Mr. Lecce said that asymptomatic testing at Thorncliffe Park and classrooms closings would help “mitigate any further spread.”

Still, Caroline Colijn, a professor at Simon Fraser University who specializes in mathematics and epidemiology, worries about asymptomatic spread in schools. “Should we be worried about transmission in schools? I think we should,” she said, adding that schools may not amplify infections, but “we know [transmission] can happen.”

Dr. Colijn said it’s important to test but also to mitigate community spread in order to reduce the exposure to students and staff in schools.

Khalil Aldroubi’s daughter started her two weeks of self-isolation on Monday after someone in her Grade 5 classroom tested positive. She had a negative test. Mr. Aldroubi has two children who attend Thorncliffe Park school. Nobody in his son’s Grade 4 class tested positive.

Mr. Aldroubi, who lives in one of the towers in Thorncliffe Park, said he was worried about his daughter not being engaged in online learning, and his ability to help her.

Despite the cases, Mr. Aldroubi said he would send his daughter back to school after her self-isolation was finished. “The most important thing for us is school,” he said.

Munira Khilji, a community advocate, said many parents are worried about the mental health of their children as they learn about positive cases in Thorncliffe Park classrooms. She said parents may not be “entirely comfortable” to send their children to school, but “they don’t have the capacity to support kids at home,” primarily because of language barriers.

Isaac Bogoch, an infectious diseases specialist at Toronto’s University Health Network, said the data coming out of asymptomatic testing in schools are important, but it’s equally important to understand where students are acquiring infections. He said that to date, there doesn’t appear to be a “tremendous amount of transmission” in schools.

“I think it’s also really important to know what burden of infection is a result from people getting this at home and in non-school environments, and how much transmission actually happens at school or as a result of school,” Dr. Bogoch said.

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