UPDATE: March 23, 2020 — The Calgary Catholic School District now reports that a fourth student has tested positive for COVID-19. The district did not identify the student or indicate which school the student attended.

"The school building has been declared safe by Alberta Health Services and at this point our buildings remain open and the situation will continue to be monitored," chief superintendent Bryan Szumlas wrote in a letter to parents Monday.

Original story below:

The Calgary Catholic School District says three students in three different schools have tested positive for COVID-19.

In a letter sent to families Thursday, the school district informed parents of the infected individuals, but said they would not be releasing the names or schools of the students.

"The principals of these schools will contact the community with an update from Alberta Health Services," wrote chief superintendent Bryan Szumlas.

Letters from principals shared with CBC News reveal that one of the students attended Father Lacombe High School in the city's southeast, and another attended St. Martha School in the city's northeast.

Szumlas confirmed two of the students had experienced symptoms while at their respective schools.

"One of the three individuals, there was absolutely no contact with the school community. So that school community is absolutely safe," Szumlas said.

The other two students were both in their schools on March 13 when they were exhibiting symptoms of COVID-19.

"[Health officials] are so thorough with doing interviews with the individuals, and trying to determine who were in close contact to those individuals, and then they reach out and they contact those people and they just continue the chain," Szumlas said.

According to the letter to families of students attending the affected schools, AHS is investigating to determine where the students contracted the illness — and who the students had contact with since then.

Students have not been in classes at CCSD since last Friday, after Alberta's chief medical officer made an announcement on Sunday, cancelling classes province-wide and informing students to stay home indefinitely amid the COVID-19 pandemic.

Even in the case of the student who was out of school, communications will be important, Szumlas said.

"We understand that students will talk, and we want to also calm rumours and to provide factual information to school communities," he said. "Our parents of Calgary Catholic, they've been very patient with us — they recognize that this is a difficult time and I want to thank them."

Szumlas emphasized the behind-the-scenes work of the custodial staff and administrators who are keeping the schools running.

"We do have a pandemic response team that meets every day for several hours to answer any questions and answers and to work on documents like that for our staff," he said.

In all three cases, the school buildings have been declared safe by Alberta Health Services.

All three students are currently self-isolating, Szumlas said.