Study reveals earlier heat risk thresholds for vulnerable seniors

Nationally, heat-related mortality has risen by nearly 17 percent per year since 2016. As a result, New York City now issues heat alerts and opens cooling centers when the heat index is forecast to reach 95 degrees Fahrenheit or higher for at least two consecutive days or a heat index of 100 degrees Fahrenheit or higher for any length of time.

Meanwhile, older adults are known to have a higher risk of heat stroke and related death, to have more heat-sensitive chronic conditions such as heart disease, kidney disease, and diabetes, and to be more likely to take medications that impair heat regulation.

To confirm who may be most at risk from the heat and at what temperature, researchers from NYU Grossman School of Medicine analyzed data from the electronic health records of patients ages 65 and older at two New York City emergency departments (ED) within the same health system. They sought to determine if patients went to EDs for heat-associated illnesses at temperature thresholds that differed from municipal heat advisories.

Published online March 20 in the journal JAMA Network Open, the study found that in the one ED that served a more climate-vulnerable population (people who are from underserved minority racial and ethnic groups and more reliant on Medicaid), patients sought heat-associated emergency care starting at a daily heat index maximum of 66 degrees Fahrenheit, with amplified risks observed between 90 and 101 degrees. This 90-degree threshold of amplified risk is lower than the thresholds that currently trigger municipal heat advisories and related cooling programming. At the site serving more White, privately insured patients (potentially a more climate-resilient population), no significant association was observed between heat and ED use in older adults.

With an already severe heat wave underway in western regions of the United States, now is the time for healthcare systems to prepare. Electronic health record data offered our team an opportunity to identify heat exposure thresholds associated with ED use in a vulnerable population, and we found that they differed from population-level trends that inform municipal warning systems."

Alexander Azan, MD, study senior author, assistant professor in the Department of Population Health

"In this study's healthcare system, we now know that ED use among vulnerable older patients spikes at around 90 degrees Fahrenheit as opposed to 95 degrees. Our hope is that other healthcare systems will leverage their own electronic health record data to identify the heat thresholds at which their patients are most at risk and target interventions appropriately," added Dr. Azan.

According to Dr. Azan, targeted deployment of heat safety interventions tailored to the unique vulnerabilities of older adults can enhance their heat adaptive capacity in ways that are not accounted for by current municipal practices in New York City, which depend on the 95-degree threshold to be initiated.

How the study was conducted

The research team analyzed the electronic health record data of patients ages 65 and older who arrived at two EDs within the same health system but 10 miles apart (referred to as ED-1 and ED-2). The investigators analyzed a total of 55,200 visits, representing 15,092 unique patients at ED-1 and 19,559 at ED-2, during May through September from 2022 to 2024. ED-1 is associated with a community-based academic hospital that serves a socioeconomically, racially, and ethnically diverse patient population. ED-2 is housed in a larger academic medical center that serves a greater share of White, higher-income patients. The proportion of patients enrolled in Medicaid at ED-1 was two times higher than at ED-2.

The study team matched each ED visit with temperature data from the LaGuardia Airport monitoring site, which is highly correlated with other major National Weather Service sites. They then calculated heat index values over other extreme heat metrics to allow for direct comparison with New York City heat advisory thresholds.

At ED-1, the risk of older adults seeking heat-associated ED care began increasing at 66 degrees Fahrenheit, with augmented risks observed between 90 and 101 degrees. The investigators observed no significant associations at ED-2. The study team roughly estimated that if a healthcare-system-based heat warning system had been triggered on days that were 90 degrees or hotter, it may have prevented approximately 116 ED-1 visits during the study period.

"By leveraging electronic health record data, healthcare systems can customize heat warning interventions to save lives and improve health during extreme heat events," said co-investigator Leora Horwitz, MD, director of the Center for Healthcare Innovation and Delivery Science at NYU Langone.

According to Dr. Horwitz, also a professor in the Department of Population Health, the study team plans to pair their identification of locally relevant exposure thresholds with a comprehensive evaluation of how social and structural risk factors may further exacerbate heat-associated ED use by older adults. Such research holds promise to inform tailored, healthcare-system-based heat warning strategies that could reduce preventable heat-associated ED use in older adults.

Along with Drs. Azan and Horwitz, NYU Langone researchers involved in the study were Evan Siau, MD, MPH; Jeremy Lu, MS; Cassandra Thiel, PhD; and Simon A. Jones, PhD.

Other study co-investigators were Genevieve S. Silva, MD, and Katie E. Lichter, MD, at the University of California, San Francisco.