What are Heat-Related Illnesses?
Heat-related illnesses (HRI), like heat exhaustion or heat stroke, happen when the body is not able to properly cool itself. While the body normally cools itself by sweating, during extreme heat, this might not be enough. In these cases, a person's body temperature rises faster than it can cool itself down. This can cause damage to the brain and other vital organs 1.
From 2018 to 2020, over 3,000 people died from excessive heat exposure in the United States (U.S.) and during the same time period, an estimated 277,000 individuals sought heat-related illness (HRI) medical care in an U.S. Emergency Department (ED) 2 3.
Extreme hot ambient temperature poses an emerging public health threat, particularly in the context of climate change and rising global temperatures 3. Today, Delaware has on average only two days over 100 degrees Fahrenheit each year. But by 2100, Delaware is expected to have as many as 28 days over 100 degrees Fahrenheit 4.
This data story explores the first report published by the Delaware Department of Health and Social Services, Division of Public Health (DPH) on heat-related illness in Delaware. The findings in this five-year report showed the burden of heat-related illnesses on the Delaware population and identified populations that were most at risk for heat-related health impacts. This information can be used to guide preparedness planning efforts, to inform extreme heat response strategies and public health messaging during a heat wave, and to evaluate and monitor future trends.
Key Heat-Related Illness Indicators
In the U.S., the average annual incidence rate of heat-related illnesses (HRI) is 26.2 emergency department visits per 100,000 people which is similar to the 25.0 rate seen in Delaware. In Delaware, approximately 250 individuals seek emergency department care related to heat-related illnesses each year. The rise in extreme temperatures poses a growing public health threat, particularly in the context of climate change and increasing global temperatures. While fatalities from adverse health effects of heat are rare in Delaware, the impact on our population and healthcare system is preventable.
Methodology
DPH extracted Emergency Department visits between April 1, 2019 to November 30, 2023, using the Centers for Disease and Control and Prevention (CDC) National Syndromic Surveillance Program (NSSP) HRI v2 Definition. This definition identifies any visits assigned an International Classification of Diseases version 10 (ICD-10) diagnosis code of T67, (Effect of heat and light), X30 (Exposure to excessive natural heat), and and/or a chief complaint text consistent with excessive exposure to environmental heat. All records were reviewed to determine if the visit met the case definition for heat related illnesses.
HRI Investigated by Race
When examining rates of ED visits among Delaware residents alone, Black Delawareans saw the highest rate of HRI visits based on the proportion of Black residents in the state compared to White patients as Other Races is the highest. However, the gap in ED visit rates across Black, White, and other races has closed and in 2023 rates across these three categories were similar.
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Heat-Related Emergency Department Visit by Race (2019-2023)
Rate per 100,000 Delaware residents
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The unhoused population is especially at risk of developing heat related illnesses. Like in other states, the amount of individuals experiencing homelessness is increasing in Delaware. Housing Alliance Delaware and Delaware Continuum of Care conduct an annual Point-in-Time (PIT) count to generate a yearly homelessness census including type of housing and household make up 7. Between 2019 and 2023, a median of 1,245 individuals were identified as experiencing homelessness, either as occupying a shelter bed or an unsheltered location such as an encampment. The U.S. Department of Housing and Urban Development reported that homelessness was about 0.12% of Delaware's population in 2023 8.
Examining Conditions that Can Increase Risk
ENVIRONMENT
Among Emergency Department visits where the location of heat exposure (indoors or outdoors) was recorded, the vast majority involved outdoor exposure. This trend has been increasing, with over 60% of visits in 2023 reporting outdoor heat exposure.
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Heat-Related Illness Emergency Department Visits by Environment (2019-2023)
Percentage of all ED visits
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Examining Health Conditions that Increase Risk
The 2024 report The Burden of Chronic Disease in Delaware shows that many Delaware residents have chronic health conditions that could put them at risk for heat-related illness 9. Seven percent of adults in Delaware said they have chronic obstructive pulmonary disease (COPD), 14% have asthma, 14% have diabetes, and 34% are overweight.
Chronic diseases were common among heat-related illness (HRI) patients visiting Delaware emergency departments from 2019 to 2023, with similar rates each year. The diseases that patients had present at the time of their emergency department visit related to heat exposure are referred to as comorbidities. Annually:
- 31% to 41% of HRI patients had a circulatory disease such as high blood pressure.
- 25% to 35% had an endocrine or metabolic disease such as diabetes.
- 16% to 22% had a mental health issue such as anxiety or depression.
- 6% to 9% had a respiratory disease such as asthma.
- 5% to 13% had a behavioral or substance use issue.
Chronic Conditions Among Heat-Related Emergency Department Visits by Year (2019-2023)
Percentage of all ED visits
Data Table for Chronic Conditions Among Heat-Related Emergency Department Visits by Year
Comorbidity | 2019 | 2020 | 2021 | 2022 | 2023 |
|---|---|---|---|---|---|
Circulatory Diseases | 39.3% | 31.0% | 40.8% | 35.7% | 41.1% |
Endocrine/Metabolic Diseases | 31.7% | 25.3% | 32.6% | 31.7% | 35.3% |
Mental Health Disorders | 13.0% | 22.4% | 13.3% | 16.3% | 12.1% |
Respiratory Diseases | 8.7% | 8.6% | 5.5% | 9.3% | 6.8% |
Behavioral/Substance Disorders | 7.2% | 12.6% | 7.8% | 7.0% | 4.7% |
Addressing Emerging Excessive Heat in Delaware
This Surveillance Report is the first of its kind published by the Delaware Division of Public Health (DPH) on heat-related morbidity in the state. The findings from this five-year surveillance report reveal a significant burden of heat-related illness (HRI) and identify the populations in Delaware that are most at risk for health impacts due to extreme heat. State agencies and non-governmental organizations can use this report to develop data-driven strategies to mitigate the effects of climate change and address future extreme heat events.
The Delaware Department of Public Health (DPH) collaborates with various agencies to address extreme heat risks and respond to heat-related illnesses (HRI) through public messaging, cooling centers, and improved healthcare capacity. In 2024, the CDC introduced clinical tools for healthcare providers to assess heat risk, focusing on vulnerable populations 10. Additionally, the Delaware Department of Labor through Safe DE provides helpful heat prevention tips and resources at their website.
The majority of heat-related illness emergency department visits in Delaware during the time of study were among working adults aged 20-64 years. The leading activities that Delawareans engaged in during heat exposure were working (both paid and unpaid) and recreation, sport, and exercise activities. The study concluded that there are disproportionately higher HRI rates among Black patients, males, individuals experiencing homelessness, and workers exposed to heat. These specific populations will likely require tailored messaging and outreach activities to encourage action.
Since 2022, DPH has conducted daily surveillance of HRI to identify trends and improve response strategies, emphasizing the need for adequate resources for effective monitoring and potential expansion to include cold weather impacts.
Technical Notes & Sources
Methodology
DPH extracted Emergency Department visits between April 1, 2019 to November 30, 2023, using the Centers for Disease and Control and Prevention (CDC) National Syndromic Surveillance Program (NSSP) HRI v2 Definition. This definition identifies any visits assigned an International Classification of Diseases version 10 (ICD-10) diagnosis code of T67, (Effect of heat and light), X30 (Exposure to excessive natural heat), and and/or a chief complaint text consistent with excessive exposure to environmental heat. All records were reviewed to determine if the visit met the case definition for heat related illnesses.
Footnotes
1
Centers for Disease Control and Prevention. (n.d.). About extreme heat and your health. CDC. Retrieved November 18, 2024, from: https://www.cdc.gov/heat-health/about/index.html
2
Spencer, M. R., & Garnett, M. F. (2022). QuickStats: Percentage Distribution of Heat-Related Deaths, by Age Group — National Vital Statistics System, United States, 2018-2020. MMWR Morb Mortal Wkly Rep, 71(808). doi:http://dx.doi.org/10.15585/mmwr.mm7124a6
3
Dring P, A. M. (2022, Nov 10). Emergency Department Visits for Heat-Related Emergency Conditions in the United States from 2008-2020. Int J Environ Res Public Health, 19(22). doi:doi: 10.3390/ijerph192214781
4
Delaware Sea Grant. (n.d.). Retrieved 2024, from Climate Change & Delaware: https://www.deseagrant.org/climate-change
5
Associated General Contractors of America. (2023, September). The Economic Impact of Construction in the United States and Delaware. Retrieved from: https://www.agc.org/sites/default/files/users/user21902/DE-US%20construction%20fact%20sheet_92023.pdf
6
U.S. Bureau of Labor Statistics. (2024, April). 37-3011 Landscaping and Groundskeeping Workers. Retrieved from Occupational Employment and Wage Statistics: https://www.bls.gov/oes/current/oes373011.htm
7
Housing Alliance Delaware. (2023, June). 2023 Point in Time Count. Retrieved from Delaware Continuum of Care: https://drive.google.com/file/d/1k4gscyQu80jhYk26txwDnWV33mcJ3H0Q/view
8
U.S. Department of Housing and Urban Development. (2023, December). The 2023 Annual Homelessness Assessment Report (AHAR) to Congress. Retrieved from: https://www.huduser.gov/portal/sites/default/files/pdf/2023-ahar-part-1.Pdf
9
Delaware Division of Public Health. (2024, June). The Burden of Chronic Disease in Delaware 2024. Retrieved from The Physical Activity, Nutrition, and Obesity Prevention Program: https://dhss.delaware.gov/dph/dpc/files/BurdenOfChronicDiseaseInDelaware2024Final.pdf
10
CDC. (n.d.). Clinical Guidance for Heat Health. Retrieved from U.S. Centers for Disease Control and Prevention Heat Health: https://www.cdc.gov/heat-health/hcp/clinical-guidance/index.html
