Alberta reported five more COVID-19 deaths over the long weekend and 619 new cases of the illness.
The latest update included cases reported over a four-day period from Friday to Monday.
The daily totals of new cases were:
By end of day Monday there were 1,692 active cases across the province, the highest total seen since May 9.
The regional breakdown of active cases was:
Calgary zone: 732
Edmonton zone: 648
North zone: 212
Central zone: 52
South zone: 38
Over that four-day period, a total of 47,406 tests were conducted, including a single-day record of 12,561 on Monday.
In all, 45 people were being treated in Alberta hospitals for COVID-19, including 10 in ICU beds.
The most recent deaths included a man and a woman in their 90s who were residents at the Good Samaritan Southgate Care Centre in Edmonton. The other three people — a man in his 50s and a man in his 80s in the Edmonton zone, and a man in 50s in the North zone — were not in continuing care.
11 cases at 11 schools
Dr. Deena Hinshaw, Alberta's chief medical officer of health, spent most of her news conference on Tuesday answering questions about a small number of illnesses among students or staff at a few schools.
"Since Sept. 1, Alberta Health Services has reported to us 11 cases that were present at 11 different schools while infectious," Hinshaw said. "This leaves approximately 2,389 schools who have had no disruption. None of these 11 cases acquired infection at school."
All schools have reopened as of Tuesday, she said. In a typical year, that would mean about 750,000 students and 90,000 staff in 2,400 schools across Alberta.
It was not unexpected that there would be cases found at some schools, she said, and given that, quick actions on behalf of schools and parents will be crucial to keeping schools safe in the days and weeks ahead.
"I also know that getting told you have tested positive or are a close contact can be upsetting for these children and their parents," Hinshaw said. "I know that it can be frustrating, after just a few days in school, that they already may need to stay home for two weeks if they are a close contact."
Public health officials will continue to evaluate the approach to assessing who qualifies as a close contact, she said. At this point, all students in a classroom are considered close contacts if a classmate was at school while infectious.
"We will assess that, as I said, and over time perhaps be able to adjust and amend that cautious approach."
Tuesday's news conference came as a growing number of possible coronavirus exposures were being reported in Alberta classrooms. Many schools across the province have reported individual cases within their populations.
CBC News has independently verified that at least 16 schools across the province were contending with individual cases either among staff, students or visitors.
Edmonton and the north
A confirmed case of COVID-19 at Ross Sheppard High, a public school in northwest Edmonton, has sent nearly 100 students into isolation.
About 96 Grade 10 students in three classes at the school need to get tested and self-isolate for 14 days, public school officials confirmed in a statement Tuesday. Provincial health officials will be reaching out to anyone who may have been in close contact with the infected individual.
The school said all affected students have been contacted and will be supported with at-home learning.
The school underwent a deep clean before classes resumed Tuesday.
This weekend, a case was identified at Archbishop MacDonald High School in Edmonton.
In a statement to CBC News on Tuesday, Edmonton Catholic Schools said a staff member at the school tested positive on Saturday. A letter was sent to parents on Sunday.
"We understand that the staff member was last in the school on Sept. 4, 2020, and physical distancing, proper use of PPE, proper hand hygiene and school protocols were consistently maintained while this staff member was at school," spokesperson Lori Nagy said in a statement.
"We have directed our custodial services team to conduct enhanced cleaning protocols in the areas identified within the building. This additional cleaning will focus on areas where the individual was present along with high touch areas and surfaces throughout the facility."
On Friday, Edmonton Catholic Schools confirmed that a student at Louis St. Laurent, a Catholic junior/senior high school in south Edmonton has tested positive for COVID-19.
A fourth case was confirmed Wednesday at École Sainte-Jeanne-d'Arc, a French-speaking Edmonton elementary school operated by the Greater North Central Francophone Education Region.
On Monday, the Fort Vermilion School Division in northern Alberta was informed that a staff member at St. Mary's Elementary School tested positive, delaying in-in class lessons until at least Sept. 21.
"The decision to transition to online learning was made due to reduced in-person staffing levels available at the schools," reads a statement from the school.
"A number of additional staff members considered close contacts are required to self-isolate for 14 days as directed by public health officials."
Individual coronavirus cases have also been identified at several Calgary schools including Divine Mercy Catholic Elementary, Bowness High School, Bridlewood School, St. Angela School, Lester B. Pearson High School, Notre Dame High School, St. Wilfrid Elementary School, St. Francis High School and Arbour Lake School.
In the case at Arbour Lake, a worker employed by the school's transportation provider tested positive.
Raymond High School in Raymond and Lawrence Grassi Middle School in Canmore are also dealing with individual cases.
"This is a very disturbing trend just days into the school year," Opposition education critic Sarah Hoffman said at a news conference Tuesday.
Hoffman said the government needs to take the number of cases in schools seriously.
She called for increased funding for Alberta classrooms to shrink class sizes. She also called on the province to adopt daily online reporting of all COVID cases in schools.
Alberta Health Services said it is compiling a list of schools with confirmed cases.
According to provincial health guidelines for Alberta classrooms, a single case in a school population will trigger an investigation.
An outbreak is declared when there are two or more confirmed cases in a school. When that happens, a letter will be sent to guardians and contact tracing will begin.
In order to trigger an outbreak response, the two cases must be confirmed within a 14-day period or be considered epidemiologically linked.
Five or more confirmed cases will mean the outbreak is publicly reported on the Alberta Health outbreak website.
In the case of an outbreak, educators will work with provincial health officials to decide whether the school should close.
Also Tuesday, the Fairmont Hotel Macdonald in downtown Edmonton reported that seven employees have tested positive for COVID-19. The hotel said it is working with Alberta Health Services on measures to mitigate risk and ensure safety, and said no guests or visitors have been affected.
During Hinshaw's last briefing on Friday, the province reported 164 new cases of COVID-19, bringing the provincial total to 1,433 active cases of the disease.
The province has completed 1,005,001 tests for the disease.