"Public Health staff are investigating to determine who may have been exposed at your school to cases of COVID-19during their infectious period", said the letters dated September 13, 2020.
None of the 42 cases identified so far have been transmitted within the school setting, she said.
There are six schools with two or more infections - four in Calgary, one in Edmonton and one in Lethbridge - but there's no indication the virus spread within those institutions.
The province's top doctor will be providing another update on Alberta's response to the COVID-19 pandemic later today.
There are now active cases 1,538 in Alberta.
There was one additional death over the weekend, bringing that total to 254.
"We should not expect daily testing to reach 19,000 tests per day", Hinshaw said.
On Friday, Hinshaw said that with "rigorous and proper precautions", the public health officials believe limited band practices, indoor singing and concerts involving wind instruments can take place safely.
"We need to look at not just the number of cases, but where the cases are being spread, who is impacted by the cases", she said.
The city of Edmonton remains in Alberta Health's watch with an active case rate of 57.9 per 100,000 people.
Alberta Health Services confirms outbreaks of COVID-19 at a southeast elementary school and a northeast high school. The first case was announced on March 5. Of the active cases, 37 are being treated in hospital and seven of those are in intensive care.
Laboratories across the province completed more than 46,000 tests over that same three-day period, including 18,919 on Saturday.
To date, 1,130,828 tests for COVID-19 have been carried out on 877,000 people.
There were 105 cases found on Sept. 11, 173 on Sept. 12, and 140 on Sept. 13.
There has been one death in Fort McMurray. Two cases are in Fort McKay. One case in the County of Vermilion River has recovered for a total of 14 recovered cases and zero active cases in the area.
A single case of COVID-19 has been confirmed in an individual associated with Escuela Vista Grande in Red Deer.