Image copyright PA Image caption One caused an oxygen mask and a saucer-shaped contraption in the gym
Ontario has seen more than 1,000 cases of carbon monoxide poisoning over five days.
Of those, the outbreak could be related to three schools affected by the concentration of a gas that smells like rotten eggs.
The unnamed gas has affected at least 300 people since last week, the Health Ministry said.
The longest possible incubation period is 24 hours.
On Christmas Day, the hydro authority in southwestern Ontario said people’s homes were experiencing a gas leak and a “sharp increase” in carbon monoxide levels.
Thousands of notifications were sent out to elderly and vulnerable residents as well as families with children.
The homes were being treated with hydrogen peroxide and then given oxygen. At least two deaths have been reported.
“We are encouraged by the health department’s investigation into this incident and the quality of care provided to those people impacted,” Ontario’s Education Minister Lisa Thompson said in a statement.
“Carbon monoxide (CO) poisoning is highly preventable,” she added.
Health Minister Christine Elliott said the “messaged” was about “the importance of maintaining common sense”.
Carbon monoxide is a colourless, odourless and tasteless gas that’s produced when fuel is burned. It is a leading cause of poisoning deaths in the US and Canada.
Kirkland Public School has suffered the most cases of the emerging Ontario outbreak. Six cases have been confirmed, and six more remain under investigation.
Three school districts – Kirkland, Greenwood School and City of Paris – will remain closed until Tuesday.
More than 1,000 cases of CO poisoning reported in the last week. Question is where it’s coming from? https://t.co/b35g3Rdgff pic.twitter.com/mEpmJgxTF4 — My Kitchen Rules (@MyKitchenRules) December 30, 2018
Another school – Parkway Middle School – has been shut. It has yet to report to authorities how it was affected.
Ontario says an alert issued on Twitter has been viewed more than 17,000 times since 18:30 GMT on Saturday.
The provincial government has estimated that four in 10 of the cases were caused by the same 11-year-old boy, Yativ Yefet Gidar.
Dasmari Gidar, one of his cousins, said the boy was playing with heating appliances at a family home in Ottawa County, north of Toronto, when the incident occurred.
“The [gas heater] exploded and he walked up to the window and took two steps. When he went back down, it went on fire,” she told CTV News.
The boy died soon after and his body was found in a park near his home on Thursday.
Mr Gidar, who was separated from his cousin in the incident, said his family members were waiting for answers.
“What is our son’s fault?” he asked CTV.
Northwestern Ontario is prone to widespread infestations of CO, due to the region’s heavily heating, agricultural industries and the use of heavy equipment, senior air quality scientists told NBC News.
The illness spreads easily because CO is present at lower levels in the home environment, said Ryan McCree of the Provincial Environmental Program.
You can hear more about Carbon Monoxide poisoning in Undercover: The Truth About Carbon Monoxide below: