Heat-related Illness

Rates of emergency department visits involving heat-related illness highest among older adults and South King County residents. 

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The impacts of climate change affect everyone’s health and can even make some health conditions worse as our summers get longer and hotter. One way to get a sense of the impact of climate change on King County residents’ health is to look at the number of heat-related illness emergency department (ED) visits that happen. Heat-related illnesses can include heat exhaustion, sun stroke, and fainting, and can also cause death.  

When thinking about counting ED visits as a rate per population, it can help to think about it like this: If we followed 100,000 King County residents for one year, the rate would represent how many residents visited the ED for a heat-related illness. In 2025, the rate of ED visits involving heat-related illness among King County residents was 9.6 per 100,000 population.  

  • Age: The highest rate of ED visits involving heat-related illness were among older adults ages 75+ at 27.0 per 100,000. Older adults are more likely to suffer from heat-related health problems. 

  • Trends: For King County residents, the rate of ED visits involving heat-related illness has generally risen over time. King County, along with the rest of Washington State and Oregon, experienced a heat dome in June 2021 that lasted about one week. The rate of ED visits involving heat-related illness during 2021 was 29.2 per 100,000. The rate was highest among older adults ages 75+ in 2021, at 152.2 per 100,000.

Additional Resources 

  • King County Climate Impacts on Health Data Dashboards show other health conditions related to climate change 

 

Notes and Sources

Source: Washington State Department of Health’s Rapid Health Information Network (RHINO) 

These data are reported by emergency departments (EDs) to the Washington State Department of Health’s Rapid Health Information Network (RHINO, which oversees the collection and dissemination of syndromic surveillance, or healthcare encounter data, for the state of Washington). Visits are grouped into syndromes based on chief complaint narrative and available diagnosis codes as well as other relevant fields from the visit record.  

Syndromic surveillance focuses on the number of visits, rather than the number of patients, so individuals with multiple emergency department visits may be counted multiple times. Because people with symptoms consistent with heat-related illness or related health outcomes might present with a non-specific chief complaint or have a diagnosis that was missed by the syndrome definitions, data do not reflect the exact number of visits attributed to these conditions. 

For more information on RHINO, click here.

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