Edmonton Public Schools has confirmed that there are three additional carriers of diphtheria at an elementary school where a student tested positive for the infection last week.

A group of individuals was contacted by Alberta Health Services who had close contact with the student at Evansdale School and tested them for the diphtheria bacteria.

Parents at Evansdale School were informed about the latest discovery on Thursday.

Alberta Health Services says people can become carriers for the infection even if they are fully immunized if they come in contact with the bacteria that causes diphtheria, but they may not display symptoms.

The principal of Evansdale says crews will be brought into the school on Thursday night to perform a deep cleaning of the building.

“I know this has been a stressful time for our school community,” Brenda Schmermund wrote in a letter to parents. “We are doing everything we can to keep students and staff safe at Evansdale School.”

According to AHS, diphtheria is spread through respiratory secretions and by direct skin contact. Symptoms include fever, sore throat, loss of appetite and feeling unwell.

AHS says the risk to the general public remains extremely low.