An East York elementary school where more than two dozen infections among staff and students were discovered following voluntary asymptomatic testing has been ordered to close temporarily.

Toronto District School Board (TDSB) spokesperson Ryan Bird said Toronto Public Health (TPH) advised the school to close until at least Dec. 9 to give them time to complete their investigation of the 26 cases among students and staff at Thorncliffe Park Public School.

"Every single time you get a COVID-19 case at a school, it's not just a case. There are unique circumstances around each case that Toronto Public Health looks into as part of their contact racing," Bird said.

It will also allow for more people to be tested so that health officials could get a better understanding of the situation in the school, Bird said

A letter from the principal was sent to parents Thursday evening to inform them of the closure.

"As a result, based on this advice, students and staff will not be permitted to enter the building until at least that time. We will share more information once we have a date for students and staff to return to school," Principal Jeff Crane said in the letter.

"During this time, our remaining classes that are not already at home will begin remote learning, and your child's teacher will be contacting you shortly to provide more information."

The school is expected to reopen on Dec. 10.

On Sunday, it was revealed that asymptomatic testing at the school resulted in 18 students and one staff member testing positive for the disease caused by the novel coronavirus.

In a letter sent to parents on Sunday, Crane said TPH detected the cases after 433 tests were processed on Thursday and Friday.

As of Dec. 3, TDSB said there have been 23 cases among students and three cases among staff.

"We had undergone a deep clean over the weekend when the test results from this most recent school-wide testing started to come in," Bird said.

"We'll do another deep clean here at the school during this closure period."

Three teachers walk off the job

Jamie Thom, the vice-president of the Elementary Teachers of Toronto (ETT), said he is glad the board has decided to close the school.

"Our position has always been that the school board has the ability to unilaterally make these kinds of determinations. The school board's position, obviously, is that they take their guidance from Toronto Public Health. But notwithstanding that, they still have the ability, under direction from the Ministry of Education, to make these kinds of decisions," Thom said in an interview with CP24 Thursday evening.

"We would have hoped that that would have happened several days ago, but nonetheless, better late than never."

Earlier on Thursday, three teachers at the school walked off the job because of the ongoing outbreak.

The Elementary Teachers' Federation of Ontario (ETFO) says there are currently 384 students and 27 teachers from a combined 18 classes that are self-isolating at home.

In an earlier interview, Bird said three out of the 30 staff members that are currently working at the school have now "begun the work refusal process."

He said their classes are being covered by other staff, and the board is working with the Ministry of Labour and the teachers to address their concerns.

ETT President Jennifer Brown said the teachers who walked off the job "don't feel safe" in the school.

"They don't necessarily have the answers from Toronto Public Health regarding why the school is still open," she said on Thursday.

"What is really problematic is that there is no standard of what… is the threshold that closes a school."

Brown said Toronto Public Health has also not been transparent about the contact tracing that has been conducted.

"What is not clear to us is the fact that there are no standards or contact tracing information shared with us from Toronto Public Health, so teachers don't know necessarily how they can determine it is a community-based issue versus a school-based issue," she said.

Bird said the school board "appreciates the concern" teachers have but noted that it takes direction from Toronto Public Health.

"We take our lead from Toronto Public Health. If we felt that it was unsafe or something else, we would be taking further action," he said.

"At this point, it is important to remember that all of our health and safety protocols... are with the idea in mind that COVID is in the schools. So, we are taking every health and safety precaution we can possible, but in the meantime, what we are trying to do is keep everyone informed."

In a statement to CP24, the Ministry of Labour said it is aware of the work refusal.

"Health and safety inspectors visited the workplace, and their investigation is ongoing."

Thorncliffe Park is one of the neighbourhoods in the GTA that has been hardest hit by the pandemic.

During a news conference on Thursday, Education Minister Stephen Lecce said the decision to close the school would have to be made by Toronto Public Health.

"Toronto Public Health, Dr. Dubey, Dr. de Villa, have provided context for why the school remains open," he said.

"They are really best positioned to provide that scientific advice, not politicians, so I will defer to their judgment. I have confidence in their leadership and I know their singular aim... is to do whatever is required, including tough actions, to keep students, staff and community safe."

Earlier this week, Lecce suggested the data indicate that transmission in the Thorncliffe Park community is far worse than what was discovered within the school.

“The principal within this school has communicated that the positivity rate compared from the community to the school is quite vast. In the community, it is roughly 16 per cent positivity whereas in the school it is roughly four per cent,” Lecce said in response to the situation at the Toronto elementary school.

“There is a four time increase of transmission happening in the community notwithstanding that those schools are right at the heart of those neighbourhoods.”

It should be noted that the 16 per cent positivity found recently in the wider neighbourhood reflects cases found among all those with symptoms and close contacts of previously identified cases, whereas the four per cent positivity found inside the school reflects a near complete profile of everyone who regularly sets foot in the building.

Lecce also boasted that “99.9 per cent of Ontario students are COVID-free.”

On Monday, NDP MPPs in the GTA called on the Ford government to roll out voluntary asymptomatic testing at all schools in communities with high rates of COVID-19 transmission.

Just last week, the province adjusted its COVID-19 testing guidance for school staff and students in Toronto, York Region, Peel Region and Ottawa to allow voluntary asymptomatic testing for a four-week period.

The province also offered school boards in the regions an additional $35 million to strengthen public health measures.

The testing pilot, which is in place for four weeks, was implemented to better track how the virus is spreading in and around schools.

Since late September, Ontario’s assessment centres would not test asymptomatic people unless they were linked to a known case.

The NDP has called the funding and four-week testing program a “half-measure.”

“Some students in some regions may be able to get tests. According to the government, the location and method for testing will vary between regions and cities, regions will have to develop their own plan,” the NDP said in a news release last week.