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First responders and Montreal police assist a woman after she lost consciousness due to the extreme heat during a heatwave in Montreal on July 5, 2018.Dario Ayala/The Globe and Mail

As episodes of extreme weather like the one now roiling British Columbia and Alberta become more common in Canadian cities, health officials will need to redouble their efforts to identify and protect vulnerable people, says a physician who investigated the impact of a deadly heat wave in 2018 in Montreal.

In British Columbia, the chief coroner, Lisa Lapointe, said Friday that an unprecedented 719 sudden or unexpected deaths had been reported to her office in the past seven days, three times the usual rate for the province.

She said the extreme weather B.C. has experienced in the past week was likely a “significant contributing factor” to the increase, and that the total number of deaths is preliminary and could still rise. She added, however, that the numbers of daily fatalities have been decreasing.

The week-long episode of extreme heat that smothered Quebec three years ago contributed to 86 deaths, 66 of them in Montreal.

During that time, Montreal police officers and firefighters checked on 42,000 dwellings, but only five of the deaths were at addresses that had been canvassed.

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Maxime Roy, a medical adviser for Montreal’s regional public-health authority, co-authored an epidemiological investigation report after the 2018 heat wave. He said in an interview that a registry of locations that were particularly prone to hot weather would have enabled emergency responders to find people who were vulnerable to heat because they were older, poorer or saddled with underlying health conditions.

“In an ideal world, we know who they are, we have a relationship of trust with them, so that what we offer to protect them from the heat is understood and acceptable to them,” Dr. Roy said.

The probe found that, while victims of extreme heat are vulnerable people, they are not necessarily isolated.

Authorities often urge people to check on vulnerable neighbours and acquaintances during episodes of extreme weather, but the investigation discovered that 72 per cent of those who died during the heat wave had been in touch with someone in the previous 24 hours. “The call to solidarity has its limits,” the report said.

Health authorities in Montreal have since tried to identify dwellings that are potential hot spots, so their residents can be redirected to cooler facilities during periods of oppressive heat.

“After 2018, we teamed up with the city of Montreal, emergency responders and community groups in an effort to identify vulnerable buildings,” Dr. Roy said.

“A vulnerable building is one constructed in a way that it traps heat, like a pizza oven – buildings with few windows, with brick walls and asphalt roofs that hold the heat. Often those vulnerable buildings house vulnerable people.”

A separate review of excess deaths by the regional public-health department in Montreal highlighted that 78 per cent of fatalities took place at home, in apartments or rooming houses with no air conditioning.

Dr. Roy’s epidemiological investigation also looked at the impact of heat islands – areas where paved surfaces, urban density and lack of green spaces can trap solar energy and further increase the local temperature by a few degrees.

People living in heat islands were twice as likely to die from the heat than those able to reside in greener districts, the investigation found.

Among the other factors that the investigation found increased the likelihood of death during extreme heat was mental illness. People with schizophrenia represent only 0.6 per cent of the Montreal population, but they accounted for more than 25 per cent of those who died from the heat wave.

People with mental illness may live in precarious conditions, and those who use anti-psychotic medications can be impaired in their ability to handle hot weather, Montreal’s director of public health, Mylène Drouin, has said.

Scott Lear, who studies population health at Simon Fraser University in Burnaby, said the timing of the B.C. heat wave has made it particularly dangerous.

Just a few weeks ago, the Vancouver region was in the middle of a period of chilly and rainy weather that many residents derisively call “Juneuary,” he noted. The sudden switch to extreme heat didn’t allow people’s bodies to adjust, meaning sweating isn’t as effective. And with temperatures not dropping significantly at night, residents haven’t been getting the reprieve they would need to recover between blasts of heat during the day.

“It’s an added stress that your body needs to deal with,” he said. “Over the course of a few days, people’s houses and apartments and condos are getting hotter every successive day.”

With a report from James Keller.

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