GUELPH -- Public health and school board officials have confirmed COVID-19 transmission inside classrooms at a French Catholic school in Guelph after previously saying the virus wasn't spreading inside the school.

École élémentaire Catholique Saint-René-Goupil has confirmed 18 cases of the virus among students and staff since the school year began, among the most of any school in Ontario.

A school-wide COVID-19 outbreak has also been declared by Wellington-Dufferin-Guelph public health.

Now, a mother of a student at the school, who asked to remain anonymous, said the public should known parents are following proper guidelines after school officials said most of the spread was happening at home, not in the classroom.

On Wednesday, the Conseil scolaire catholique MonAvenir school board said transmission had not occurred at the school.

But in a letter sent to parents on Wednesday, WDG public health said approximately half of those who tested positive acquired their infection from classmates at school and half were exposed outside the school.

The letter also said siblings of students where the first case originated are catching COVID-19 at home.

“We also saw unfortunately that there was some social gatherings and some outside activity that were occurring at the school, causing it to spread even further,” said Dr. Nicola Mercer, medical officer of health for the WDG health unit. “We did have transmission within the school, which is now controlled. So there was a classroom and we did see it in that particular environment.”

The school board apologized for the confusion while also pointing to the letter telling parents that interactions inside and outside the school have contributed to the outbreak

“Sorry to hear that our communication was taken that way. It was absolutely not our intent,” said Virginie Oger, a spokesperson for Conseil scolaire catholique MonAvenir.

“In this particular school we did have a transmission within the school that is now well controlled, and that class is back at school,” Dr. Mercer said.

One parent said they appreciate how the school has handled the COVID-19 outbreak.

“I think it’s very challenging to see the numbers at this point. But I feel safe that the school is following all the protocols, that they are working closely with public health,” Dayami Ramirez, a parent of a student at the school said.

Despite the high number of cases at the small, 244-student school, Saint-René-Goupil remains open.

Dr. Mercer said vaccinations and the creation of cohorts have led public health to feel it is safe to not shut down the entire school.

“We would only close a school if there was transmission that was occurring classroom to classroom and multiple times within the school. There’s a really high bar to close a school,” Dr. Mercer said.

She said with the increased transmissibility of the Delta variant, public health measures have been increased in the region.

Now household members of high-risk contacts are also being asked to stay home, resulting in more children being asked to isolate.