An Edmonton elementary school student has been diagnosed with a rare and potentially deadly infection.

CBC News obtained a copy of a letter shared with families at Evansdale School on Friday alerting them to a confirmed case of diphtheria.

Alberta Health Services is contacting a small group of people who may have had close contact with the student as a precautionary measure, said spokesperson Sabrina Atwal.

AHS declined to provide further details about the case or the school involved, citing patient privacy.

"No other cases have been identified and the risk to the public remains extremely low," Atwal said in a statement Sunday.

Diphtheria is a bacterial infection of the nose and throat. Symptoms include fever, loss of appetite and feeling unwell. In severe cases, the neck can swell. Life threatening complications include upper airway obstruction.

The infection can cause severe breathing problems, heart failure and paralysis.

Up to one in 10 people who get diphtheria die, according to Alberta Health Services.

At least third case in Alberta in three years

The vaccine is offered free of charge through Alberta's publicly funded immunization program.

The latest case is at least the third in Alberta in the past three years. An Evansdale student was also diagnosed in 2017.

New Brunswick and Ontario are the only provinces that require students to prove they're immunized against a range of diseases before they enter the classroom, with limited exceptions.

Public Health Ontario has not reported a case of diphtheria in that province since 1995.

Diphtheria was one of the most common causes of death among Canadians under five years of age before the vaccine was introduced in 1926, according to Health Canada. There were 9,057 cases reported in 1924, the largest tally recorded in Canada.

The number of cases fell dramatically after the introduction of the vaccine.

There were 17 cases reported across Canada between 1996 and 2016, an average of less than one case per year.