Ontario health officials are investigating three deaths that may have been the result of a powerful heat wave that drove temperatures as high as 40 C, but it will take weeks to months to get a clear answer.

That number is small compared to the dozens of potential heat-related deaths in Quebec, where as of Monday, up to 70 people may have died as a result of complications related to the hot weather.

The difference is that Ontario has a stricter definition of what constitutes a heat-related death, Ontario’s chief coroner Dr. Dirk Huyer explained Tuesday.

In Quebec, a death is deemed heat-related even if a person has a pre-existing chronic condition, such as a respiratory disease, that may be exacerbated by severe heat. Earlier this week, health officials in Montreal said that most of the heat-related deaths were the result of chronic illnesses.

In Ontario, only “accidental” deaths where heat is believed to be the sole factor -- such as a child being left alone in a hot car – are investigated as heat-related.

“So our definition, what we would investigate, would be accidental deaths that are directly affected by the heat as opposed to a natural disease process,” Huyer explained in a media conference call. “We are not notified of deaths that are deemed natural.”

All three Ontario deaths occurred in last the four days, but Huyer would not say exactly where, citing privacy concerns.

In each case, an investigation has been launched to determine whether heat was the primary cause of death.

Those investigations could take weeks to months because investigators need to collect a wide range of evidence. Interviews with family members, an autopsy and analysis of medical records are part of the process.

“And sometimes when the initial tests are done, there may be more tests that may be done from that,” Huyer said.

Temperatures in the mid-30s have gripped large parts of Ontario, Quebec and Atlantic Canada in the past week, but humidex values have often made those conditions feel even hotter. Environment Canada called the weather the “most significant heat event in the past few years.”

The heat wave was so intense that a stretch of highway near Windsor, Ont. buckled on July 1. On Parliament Hill, only 6,000 people turned out for the annual Canada Day lunchtime show as the humidex value at the Ottawa airport reached a record-setting 47 C.

In Montreal, morgues have become so overcrowded that the coroner’s office has partnered with a local funeral home to house the influx of bodies. Officials estimate that more than 15 bodies arrive almost every day.

In Ontario, hospital visits linked to the heat have spiked, according to Dr. David Williams, Ontario’s chief medical officer of health. The increase peaked on Canada Day and eventually returned to baseline levels on July 7.

People need to take extreme heat warnings seriously, Huyer said, and make a point of checking on family members and friends who may be more vulnerable.

Huyer said he’s concerned that the length and severity of heat waves could worsen in years to come due to climate change.

“We need to take this seriously because these events seem to be happening more frequently,” he said.