If we don’t know the extent of a problem, we can’t or won’t do much to fix it. That’s what’s going on with heat-related mortality. Until we know how many people are dying of heat exposure and who they are, most government officials and policymakers can and will ignore the existential danger of extreme heat.
This past week Planet Earth experienced its hottest day since record-keeping began. It seems like a good time to review how physicians, coroners, and medical examiners are investigating the possibility of heat-related mortality during heat waves.
How does Heat Kill Humans?
A 2023 research study examined the physiology of heat survivability in excruciating detail. A sample statement: “A human would experience heat stroke death from hyperthermia on 99.9% of occasions when an individual’s core temperature (Tcore) exceeds 43 °C (109.4°F).” The bad news? People can die at (much) lower temperatures depending on humidity, sun or shade exposure, age, body size, and health conditions.
Besides heat stroke, excess heat kills by cardiovascular collapse (heart attacks, heart failure) and kidney failure. One of the reasons hydration is important during periods of hot weather is to maintain kidney function. We know this because of research on acute and chronic kidney disease in young male agricultural workers in Central America. High rates of hypertension, diabetes, and vascular disease—all risk factors for kidney disease—in the United States suggest that in the longer term increasing temperatures will mean increasing deaths from renal failure.
What is a Heat-Related Death?
Part of the reporting problem is lack of a standard definition or protocol for heat-related death. The three criteria used by the Cook County Medical Examiner’s office (CCMEO) during the 1995 Chicago heat wave still make sense today.
- Core body temperature of the decedent greater than or equal to 105 F (greater than or equal to 40.6 C) at the time of or immediately after death
- Substantial environmental or circumstantial evidence of heat as a contributor to death (e.g., decedent found in a room without air conditioning, all windows closed, and a high ambient temperature)
- Decedent in a decomposed condition without evidence of other cause of death and with evidence that the decedent was last seen alive during the heat wave period
A big problem is that taking someone’s temperature during a medical emergency just doesn’t happen. By the time someone calls 9-1-1, by the time EMS stabilizes and transports a patient, by the time someone pronounces the patient dead in the emergency room, by the time a medicolegal death investigator arrives and—finally—takes a temperature, that temperature is much lower than it was at the time of death.
CDC and NAME guidance on Heat-Related Mortality
CDC developed and published Death Scene Investigation after Natural Disaster or Other Weather-Related Events: A Toolkit in 2017. The first section is about investigating deaths where heat may have been a factor.
A more recent resource is the National Association of Medical Examiners (NAME) position paper on disaster-related deaths. NAME also includes extreme temperatures as a type of disaster.
Despite this CDC and NAME guidance, most C/MEs continue to under-report heat-related deaths. Reasons include lack of resources and incomplete information-gathering about the death. Some cases never even make it to the C/ME. Physicians in the community may fail to recognize heat as a contributing factor when someone dies of a heart attack, stroke, or kidney failure. Even when physicians suspect heat exposure, they may not be aware they must report such deaths to their county’s C/ME.
Hot Spots
Since Planet Earth experienced its hottest day on record this month, I took a look at heat death reporting in some of the hottest spots in the United States. For each location, I checked CDC’s Heat and Health Tracker to determine the location’s Social Vulnerability Index (SVI). The SVI is a measure of social and economic factors that impact vulnerability to events like pandemics or environmental disasters.
Southern Nevada Health District (includes Las Vegas)
The average summer daytime high in Clark County (home of Las Vegas) is 104. Although Clark County has a heat safety initiative called Stay Cool, it still has a huge heat death problem. That’s due in part to its high SVI.
I couldn’t find an annual report on the Clark County Coroner’s Office website, but the county’s Public Information Office provided a link to a 2024 county heat death report. That report notes only six heat-related deaths as of mid-2024, compared with 293 confirmed deaths in 2023.
The 2023 Southern Nevada Health District heat report noted that heat was the cause of slightly more than 50% of the 293 deaths, while the others were deemed “heat-related.” The report did not include criteria for these two designations. Some facts: 73% of heat deaths were in men, most happened outside, and most were urban (in Las Vegas proper rather than the rest of the county). Coroners in Southern Nevada counties provided data on how many were homeless. Twenty-four percent of heat deaths were in unhoused individuals with another 19% not having a known address. That’s shocking considering that approximately 1% of the Las Vegas population was homeless in 2023.
Maricopa County Arizona (includes Phoenix) takes Heat Doom seriously
Known as the hottest city in the United States, Phoenix has a moderate to high SVI. In 2023, 645 people died of heat-related causes in Maricopa County. Four hundred those deaths were in Phoenix. Scientific American characterized the dire situation there as “a collision of homelessness and record-setting heat waves.” Among the dead were 290 unhoused people. The city is currently using temporary pandemic relief funding to expand cooling centers and increase times the centers are open.
Arizona medical examiners are setting the standard for identifying and reporting heat deaths. In May of this year, NPR noted that the work those investigators are doing “could redefine how the United States understands the growing cost of climate change, because right now, the human toll of climate-worsened disasters is dramatically undercounted.”
What do thorough death investigators like forensic pathologists Greg Hess (Pima County) and Jeffrey Johnston (Maricopa county do? Well, they seriously investigate, carefully recording and tracking down temperatures (people and environments) and painstakingly evaluate the circumstances of each potentially heat-related death. What they do isn’t rocket science: it’s remarkably like the readily available protocol CDC provides in its Toolkit.
Bexar County TX (includes San Antonio)
Back in February, environmental activist and reporter Greg Harman of Deceleration News in South Texas contacted me about the death of Albert Garcia, an unhoused man, during a 2023 San Antonio heat wave. The subsequent news report (note: I was a source for the article) questioned why the Medical Examiner did not categorize Garcia’s death as heat-related. Harman and Deceleration have posted an online petition demanding better recording of heat-related mortality.
The most recent Bexar County ME report is from 2022. I couldn’t find any mention of heat-related deaths. The city of San Antonio has a heat-related illness dashboard but it also fails to mention heat-related deaths. Bexar County has a high SVI: more than 17% live in poverty and over three thousand were homeless in 2024 (888 were unsheltered).
Southern Florida (includes Miami-Dade)
Farmworker Efraín López García, a Guatamalan immigrant, was working in a Miami-Dade County field when he died during extreme heat in July 2023. His case illustrates the challenges of attributing a death to heat exposure. Despite a public outcry about working conditions during the heat, the ME ultimately determined the cause of death to be complications of diabetes mellitus, with cocaine use as a contributory factor. He added that there was “insufficient evidence to opine that the decedent died as a primary result of heat stroke.”
I couldn’t find an annual report on the Miami-Dade ME website either. After contacting the office, I received a link to this Florida vital statistics database. Veronica Melton-Lamar, Medical Records Manager for the Miami-Dade Medical Examiner Department, informed me by email that there were two heat-related deaths in Miami-Dade in 2023 and none so far in 2024.
Some believe that officials are grossly underreporting heat-related deaths in Florida and elsewhere. The reported number for Miami-Dade does seem low, given its high SVI and extreme heat. If it really has so few heat-related deaths, it would be helpful to know why.
How can we improve reporting of heat-related mortality?
My admittedly aspirational short (yes, really) list:
- Update and reactivate CDC training on certification of disaster-related deaths
- Break out environmental exposure deaths (like drug deaths, falls, and motor vehicle collisions) on accidental death statistics
- Collect and publicize heat-related deaths in each county
- Establish a National Environmental Death Reporting System—analogous to the National Violent Death Reporting System, Drug Overdose Reporting System, and Infant/Child Death Reporting
- Increase training and presentations about heat-related death certification at professional conferences (IACME, NAME, AAFS, MDI training programs, medical conferences)
- Increase awareness that all work-related deaths—including those associated with heat exposure— are reportable to OSHA.