PHOENIX (AP) — Another seven heat-associated deaths were confirmed over the last week in America’s hottest big metro, health officials reported Wednesday, amid a blistering heat wave with daytime highs over 110 F (43.3 C) and overnight lows not dropping below 90 F (32.2 C).

Maricopa County, the biggest county in Arizona and home to Phoenix, reported that its health department has confirmed 25 heat-associated deaths this year as of Saturday since the first one was recorded in April, with 249 more under investigation.

That's seven more heat-associated deaths for the year since 18 were reported as of July 15, when there were 69 additional deaths under investigation.

As of the same time last year, there were 38 heat-associated deaths and 256 more listed as under investigation.

The region's county and city governments, hospitals, schools and non-profit groups that operate several hundred cooling and hydrating stations across the area are closely watching the confirmed death figures, along with daily forecasts from the National Weather Service.

Phoenix hit 27 consecutive days above 110 F (43 C) on Wednesday. There has not been a single overnight low under 90 F (32.2 C) since July 9, which means people's bodies aren't adequately recovering after the sun goes down, making them susceptible to heat illnesses that can result in death.

WHAT EXACTLY ARE HEAT-ASSOCIATED DEATHS?

Maricopa County comes up with its heat-associated death figures by adding together heat-caused deaths, in which heat or heat exposure is listed on the death certificate as the primary cause of death, with heat-related deaths, in which heat exposure is listed as a secondary cause.

Cases listed as under investigation are deaths in which the county's Office of the Medical Examiner suspects that heat played a role.

WHAT DO THE NEW NUMBERS MEAN?

While the numbers confirm that people are continuing to die in Maricopa County from causes associated with the heat, it's hard to draw firm conclusions.

David Hondula, who oversees heat response and mitigation for the City of Phoenix, warned earlier this month against coming to quick conclusions.

“My advice would be it’s a little early to really interpret the mortality data from the county,” he said.

Sonia Singh, supervisor with the Maricopa County Public Health Department's communications office, said the update means only “that seven additional deaths were confirmed in that time frame, not necessarily that they occurred in that time frame.”

“We will likely not have a complete count of deaths resulting from this heat wave for some time,” Singh said in a written statement. “This is for a couple reasons: 1) the deaths are reported from multiple sources and may not come in to Public Health right away, and 2) these deaths sometimes take a while to go from a suspect case to a confirmed case.”

For instance, toxicological tests that can takes weeks or months after an autopsy is conducted could eventually result in many deaths listed as under investigation being changed to confirmed.

An example of this was seen in last year's numbers.

At the end of last year, Maricopa County had reported there were 378 heat-associated deaths confirmed for all of 2022. By this spring, that number had grown to 425, the current number, as more deaths that were under investigation were confirmed as heat-associated. More than half of the deaths occurred in July in what was the hottest summer on record — a record that is likely to be broken this year.

WHO HAS BEEN DYING IN THE HEAT?

Both this year and last, about 80% of the people who died fell ill when they were outdoors, and more than a third were people experiencing homelessness. Over half of all heat-associated deaths involved drug use.

All of the people who died indoors both years were in uncooled environments. Most of the people had an air conditioner that was nonworking, turned off or nonexistent. In three cases this year, there was no electricity to power a cooling system.

The death of a 72-year-old woman in metro Phoenix five years ago when her electricity was turned off over a $51 debt forced utilities to change their rules.

WHAT ROLE DOES THE URBAN HEAT ISLAND EFFECT PLAY IN PHOENIX?

An analysis published Wednesday says Phoenix would be consistently 7 F (3.9 C) cooler, every day and night, if not for the heat created by the city’s built environment, also known as the heat island effect.

The phenomenon makes every city hotter. In Phoenix, it pushes temperatures to extremes, said Jen Brady, research manager with Climate Central and one of the analysis’ authors.

“Some cities have a lot less to play with before people are at very high risk for health impacts,” Brady said.

About 17,000 residents live in areas of Phoenix where the urban surroundings add at least 10 F (5.6 C) to what they would experience otherwise.

WHAT'S HAPPEPNING IN OTHER PARTS OF ARIZONA?

Other parts of Arizona, especially the southern Yuma, Pima and Santa Cruz counties, are also seeing dangerous, record high weather that has resulted in deaths, but only Maricopa County releases a weekly online update on heat-associated deaths.

The Yuma County Sheriff’s Office said farmworker Dario Mendoza, 26, died after collapsing in the fields July 20 after the high reached 116 F (46.7 C) in the agricultural region. The Yuma County medical examiner said the death was heat-related, a sheriff’s spokesperson said.

The Arizona Division of Occupational Safety and Health is investigating.

The Tucson sector of the U.S. Border Patrol reported that during the first three weeks of July it had received 151 calls for help and rescued more than 1,100 migrants in the sweltering desert near the U.S.-Mexico border. Agents have also encountered human remains.

"Arizona’s west desert is the most dangerous place to cross the southwest border, and this intense heat only increases the chances for tragedy,” said Joel D. Garcia, patrol agent in charge of the Ajo Station.

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Associated Press writer Mary Katherine Wildeman contributed to this report from Hartford, Connecticut.

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