Heat-Related Illness on the Rise in the U.S., Study Finds

ARLINGTON, Va. -- The incidence of heat-related ailments -- including heat stress, heat exhaustion, and heat stroke -- has been increasing, Isabelle Creavin said at the Health Datapalooza meeting here sponsored by AcademyHealth.

Creavin is special assistant to the president at FAIR Health, an organization with the largest repository of private health claims data in the U.S. Creavin presented data from a FAIR Health study published in December 2022 which analyzed 39 billion health claims filed in the months of May through December during the years 2016 through 2021, looking for those dealing with heat stress, heat exhaustion, and heatstroke. Claims were analyzed by age and gender as well as the percentage diagnosed with each type of illness, Creavin said at her presentation on Thursday.

Heat stress, the least severe of the three illnesses, is characterized by fainting, heat cramps, heat fatigue, and swelling. "Every month from May to September, the percentage of patients diagnosed with heat stress increased during one month in 2016 to the same month in 2021," with the greatest increase, 37.8%, occurring from May 2016 to May 2021, and the smallest increase, 6.7%, occurring from August 2016 to August 2021, she said. For most months, the greatest percentage of patients diagnosed with heat stress occurred in 2021, although there were a couple of exceptions.

Age also appeared to play a role, as people 65 and older were more than twice as likely to be diagnosed with heat stress as the next most likely age group, those 55 to 64, Creavin said.

As for gender, more men than women were diagnosed, with men comprising 52% of heat stress patients compared with 48% for women. "This is opposite of the gender distribution we typically see for most other conditions in the FAIR Health data collection," said Creavin, adding that "the findings of other researchers also show that women are more likely than men to visit physicians and make use of healthcare services generally," making this finding even more unusual.

For heat exhaustion, the increases from 2016 to 2021 were bigger than those for heat stress, with the largest increase in diagnoses being 52.5% from June 2016 to June 2021. The smallest increase was "still quite notable" -- an increase of 25.9% from September 2016 to September 2021, Creavin said. For the month of June, 2021 was the peak year for diagnosing heat exhaustion, while for all other months, 2020 was the peak year.

Similar to heat stress, diagnoses of heat exhaustion -- characterized by heavy sweating and rapid pulse -- increased with age, and the greatest percentage was found in the oldest age group. "Among the 65-and-older population, heat exhaustion affected 2.61% of all patients who received medical services nationally," while "the smallest percentage of patients diagnosed with heat exhaustion was in the 0-to-18 age group, at 0.57%," she said.

And while males were once again diagnosed with this heat-related illness more often than females, the difference between genders was greater with heat exhaustion, with 64% of patients being male and 36% being female. "As has been noted by other researchers, possible reasons for that association may include occupational factors, such as the greater likelihood of men working in outdoor jobs such as construction or agriculture," said Creavin.

For heatstroke -- the most severe of the three types of heat-related illness studied -- the year in which the highest percentage of people were diagnosed with the illness depended on the month studied, she said. For example, for the month of July, the peak year for heatstroke diagnosis was 2018, while for August and September it was 2021. In patients with heatstroke, the body is unable to cool itself down, and the patient may stop sweating.

The gender distribution for heatstroke patients "was the same as that for heat exhaustion, with males constituting 64% of the diagnoses and females 36%," she said. In every age group, males were diagnosed with heatstroke more than females. "The greatest percentage of females with heatstroke was in the age group 0 to 18, and the greatest percentage of males with heatstroke was in the age group 55 to 64."

During a question-and-answer session, Creavin was asked how concerned people should be about these findings. "It is quite alarming that between June 2016 to June 2021 there was a 50% increase in heat exhaustion, and I can't really tell you how you should feel about that," she said. "But I think moving forward, we definitely need more studies. This brings to light, really, how severe this increase is -- that it's just a couple-year period as compared to decades before."

"We're just hoping that it's these kinds of studies that really help people think more about what state of crisis we're in," she added. "This [data] can certainly be used by policymakers to really think about how they can move forward with heat-related illnesses and climate change."

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