Last summer was the hottest ever recorded in the United States, and heat-related health emergencies also reached record-high levels in some parts of the country.
In the United States, the vast majority of emergency department visits for heat-related emergencies — such as heat stroke, heat cramps and sunburns — happen during the warm season that lasts from May through September, peaking in July and August, according to surveillance data collected by the US Centers for Disease Control and Prevention.
During the warm season last year, heat-related illnesses accounted for a 20% larger share of emergency department visits than they did in the five previous seasons. Data from hundreds of emergency departments across the country shows that 180 out of every 100,000 total visits were due to heat-related illness in 2023, compared with 151 out of every 100,000 total visits from 2018 to 2022.
The risks of peak heat are also becoming more extreme, with the rate of heat-related emergency department visits surging above peaks from previous years and other parts of the same warm season. In July and August of last year, there were more than 300 heat-related emergencies for every 100,000 total emergency department visits, CDC data shows. That’s nearly 50% higher than the average peak rate from 2018 to 2022, and about three times higher than the rate from other warm-season months in the same year. In previous years, risk during the peak heat season was about twice as high as in other warm months in the same year.
The US Department of Health and Human Services considers a day to be an extreme heat day if the temperature rises above 95% of the average historical temperatures in that region. The CDC assessed trends in heat-related emergency department visits against a similar threshold.
In 2023, all regions of the US experienced at least one day where the rate of heat-related emergency department visits reached an extreme level, topping 95% of rates from 2018 to 2022. In a particular southern region — encompassing Arkansas, Louisiana, New Mexico, Oklahoma and Texas — emergency department visits for heat-related illness reached this extreme level for more than a third of 2023’s warm season, including a period of 16 consecutive days. In four southern regions, comprised of 21 states, 2023 brought more days with extreme rates of emergency department visits for heat-related illness than any other year on record.
“Deaths and illnesses associated with heat exposure are a continuing public health concern as climate change results in longer, hotter, and more frequent episodes of extreme heat,” CDC experts wrote in a report that published Thursday. “Near real-time monitoring of weather conditions and adverse health outcomes can guide public health practitioners’ timing of risk communication and implementation of prevention measures associated with extreme heat.”
Last August, HHS’ Office of Climate Change and Health Equity in partnership with the National Highway Traffic Safety Administration launched a dashboard that uses data from the National EMS Information System to track the rates of EMS responses to 911 calls for heat-related illness and injury. Data updates weekly with a lag of no more than two weeks, showing where states and counties fall relative to the national average and disparities by age, race, gender and urban-rural area.
“Heat is the most lethal of all types of extreme weather and heat exposure is worsening with increasing global warming,” Dr. John Balbus, acting director of the HHS Office of Climate Change and Health Equity, said at the time. “But existing data on heat-related deaths don’t shed light on where people actually fall ill. This new dashboard makes it possible to see where the needs are greatest, plan for the future, and save lives.”
CDC has also used data collected from health departments that participate in the National Syndromic Surveillance Program Surveillance System for the Early Notification of Community-Based Epidemics (ESSENCE) to monitor heat-related health trends. In June and August, high levels of heat-related emergency department visits prompted the agency to issue public health alerts, according to Thursday’s report.
The new CDC analysis may underestimate the prevalence of heat-related illnesses since it doesn’t capture cases among people who sought treatment elsewhere, and the Covid-19 pandemic may have generally affected health care utilization patterns. Broad regional analysis may also obscure more local trends.
Understanding regional trends and differences in emergency department visits for heat-related illness can help public health officials better develop and implement intervention strategies, according to the new CDC report.
“Effective implementation of heat mitigation strategies is associated with social determinants of health,” the authors wrote, such as access to air conditioning, cooling spaces and reliable power grids.
Certain groups are particularly susceptible to the health risks of heat waves, including children and adults with underlying health conditions, pregnant women and outdoor workers. In July, President Joe Biden asked the Department of Labor to issue a “hazard alert” for heat and ramp up enforcement to protect workers from extreme heat.
“For years, heat has been the number one cause of weather-related deaths in America. And workers, including farmworkers, farmers, firefighters, and construction workers, are disproportionately impacted by extreme heat,” the administration wrote in a statement on the “hazard alert” proposal.