More than 300 suspected heat-related deaths in the Phoenix area are being investigated

More than 300 deaths believed to be linked to this summer’s record-breaking heat wave are being investigated in a single Arizona county, official statistics showed Thursday morning.

A heat dashboard for Maricopa County, which includes Phoenix and is the fourth most populous county in the U.S. with 4.4 million residents, found that 322 deaths in the year ending July 13 were suspected to be due to heat-related illnesses – a huge increase from the previous year.

Nearly 100 of these suspected heat-related deaths occurred in a single week, July 7-13, when temperatures reached 46 degrees. Previously, parts of Arizona, Nevada and Texas had experienced the hottest June on record.

According to the data, there have been 23 confirmed heat-related deaths in the county this year, 17 of which were directly caused by the heat and 6 were “heat-related.”

“We know that June was hotter than last year,” Nick Staab, deputy medical director for the Maricopa County Health Department, told NBC affiliate KPNX in Phoenix. “We know that with these higher temperatures comes an increased risk of heat-related death,” he said.

According to a recent count by NBC News, there have been at least 73 heat-related deaths in the United States so far this year.

And the extreme heat in the Southwest is not over yet. Temperatures of up to 46 degrees are expected in Phoenix on Friday, so a heat advisory has been issued through Saturday night. There is even a chance of some thunderstorms on Thursday and through the rest of the week.

In comparison, during the same period last year, there were 12 confirmed heat-related deaths and 106 cases under investigation, KPNX reported.

County data shows that 70% of fatalities were male, while drugs played a role in just over half of the deaths and 39% of victims were homeless. Alcohol played a role or contributed to 13% of the deaths.

“A heat warning means there will be a period of very hot temperatures even by local conditions. Actions should be taken to reduce the impacts of extreme heat,” the National Weather Service said.

Maricopa residents can call 211 to find the nearest cooling center and request free transportation. Firefighters in Phoenix began using ice packs this year to aggressively combat heat stroke and lower patients’ body temperatures.

Maricopa’s data is broken down by zip code, and the area with the most heat-related deaths is the city of Mesa, east of Phoenix.

Last year, there were 579 confirmed and 56 suspected heat-related deaths in Maricopa, compared with 386 in 2022, according to data from the Department of Health and Human Services.

According to DHH, a quarter of last year’s deaths occurred indoors, with two-thirds of those victims having air conditioning systems that were not working properly.

The heat dashboard was introduced by the county in May to better track illnesses and deaths resulting from extreme temperatures.

NBC News has contacted Maricopa County for comment.