Nationally, heat-related mortality rates have increased by nearly 17 percent annually since 2016. As a result, New York City now issues heat warnings and opens cooling centers when the heat index is predicted to reach 95 degrees Fahrenheit or higher for at least two consecutive days, or when the heat index is predicted to reach 100 degrees Fahrenheit or higher.
Older people, on the other hand, are known to be at higher risk of heatstroke and related mortality, have chronic heat-sensitive illnesses such as heart disease, kidney disease, and diabetes, and are more likely to take medications that impair heat regulation.
Researchers at New York University Grossman School of Medicine analyzed data from electronic medical records of patients 65 and older from two New York City emergency departments (EDs) within the same health system to see who is most at risk from heat and at what temperatures. They sought to determine whether patients presented to emergency hospitals for heat-related illnesses at temperature thresholds that differed from municipal heat advisories.
Published in an online journal on March 20th JAMA network openThe study found that in one ED serving a climate-vulnerable population (those in underserved minority racial and ethnic groups who are highly dependent on Medicaid), patients sought heat-related emergencies starting at daily heat index peaks of 66 degrees Fahrenheit, with an amplification of risk observed between 90 degrees Fahrenheit and 101 degrees Fahrenheit. This 90-degree threshold for amplified risk is lower than the threshold that currently triggers municipal heat advisories and associated cooling programs. No significant association between fever and ED use among older adults was observed in facilities serving more white, privately insured patients (a potentially more climate-resilient population).
With severe heatwaves already occurring in the western United States, now is the time to prepare health systems. Electronic health record data provided our team with the opportunity to identify heat exposure thresholds associated with ED use in vulnerable populations, but we found these to be distinct from population-level trends that inform municipal alert systems. ”
Alexander Azan, MD, lead study author, assistant professor in the Department of Population Health
“The health systems in this study found that among vulnerable older patients, ED use spikes around 90 degrees Fahrenheit, not 95 degrees Fahrenheit. Our hope is that other health systems will leverage their own electronic health record data to identify the fever thresholds at which patients are most at risk and target appropriate interventions,” Dr. Azan added.
Targeted deployment of heat safety measures tailored to the unique vulnerabilities of older adults can increase their ability to adapt to heat in a way that New York City’s current municipal practices, which rely on a 95-degree starting point, do not take into account, Dr. Azan said.
How to conduct research
The research team analyzed electronic medical record data for patients aged 65 and older who arrived at two acute care hospitals (called ED-1 and ED-2) located 16 miles apart within the same health system. Researchers analyzed a total of 55,200 visits representing 15,092 unique patients in ED-1 and 19,559 unique patients in ED-2 between May and September from 2022 to 2024. ED-1 is affiliated with community-based academic hospitals that serve a socio-economically, racially and ethnically diverse patient population. ED-2 is housed in a larger academic medical center with a high proportion of high-income white patients. The proportion of patients enrolled in Medicaid in ED-1 was twice as high as in ED-2.
The researchers matched each emergency worker’s visit with temperature data from the LaGuardia Airport monitoring site, which is highly correlated with other major National Weather Service sites. We then calculated heat index values based on other heat indexes so that they could be directly compared to heat advisory thresholds for New York City.
In ED-1, older adults’ risk of seeking heat-related ED care began to increase at 66 degrees Fahrenheit, and increased risk was observed between 90 and 101 degrees Fahrenheit. Researchers observed no significant association for ED-2. The researchers roughly estimated that about 116 ED-1 visits could have been prevented during the study period if the health system-based heat warning system had been activated on days with temperatures above 90 degrees.
“By leveraging electronic health record data, health systems can customize heat warning interventions to save lives and improve health during extreme heat events,” said co-investigator Leora Horwitz, M.D., Ph.D., director of NYU Langone’s Center for Healthcare Innovation and Delivery Sciences.
Horwitz, who is also a professor in the Department of Population Health, said the research team plans to combine identification of regionally relevant exposure thresholds with a comprehensive assessment of how social and structural risk factors further exacerbate heat-related ED use among older adults. It is anticipated that such studies may provide customized heat warning strategies based on healthcare systems that can reduce preventable heat-related ED use in older adults.
With the doctors. Azan and Horwitz researchers at NYU Langone who were involved in the study were Evan Siau, MD, MPH; Jeremy Lu, MS; Dr. Cassandra Thiel. and Dr. Simon A. Jones.
Other study collaborators are Genevieve S. Silva, MD, and Katie E. Lichter, MD, of the University of California, San Francisco.
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Reference magazines:
Shaw, E. Others. (2026). Extreme urban heat and emergency department visits among the elderly. JAMA network open. DOI: 10.1001/jamanetworkopen.2026.2645. https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2846734
