When temperatures soar, emergency physicians typically expect more cases of dehydration and heat stroke. But a new Northwestern University study suggests extreme heat is connected to a much broader range of health problems treated in emergency departments and urgent care clinics, including skin conditions, kidney problems, multiple sclerosis and injuries from traffic accidents.

The findings, published Aug. 26 in Science Advances, could help emergency departments and health care systems better prepare for heat waves, which are becoming more frequent with climate change. Heat-related illness can be difficult to track because medical records often document the condition being treated without indicating whether extreme temperatures may have contributed.

Researchers used an innovative approach inspired by methods from genomics research to examine 1,803 diagnoses across nearly 1 million emergency department and urgent care visits in Chicago between May and September from 2011 to 2023. They identified 33 diagnoses associated with extreme heat exposure, including several conditions that have received relatively little attention in previous heat-related health research.

“If we’re only tracking the more commonly known heat-related illnesses, we’ll underestimate the true heat-related health burden, which could result in vulnerable people and communities being overlooked,” said corresponding author Hyojung Jang, a Ph.D. candidate in biostatistics at Northwestern University Feinberg School of Medicine. She said protecting people and communities most vulnerable to the effects of climate change is an important public health responsibility.

Among the diagnoses associated with extreme heat were skin rashes and swelling, acute kidney failure, multiple sclerosis, mental and behavioural disorders, insect bites and stings, traffic accidents, assault and firearm-related injuries. Co-author Daniel Horton said previous research has found that extreme heat can increase stress and aggressive behaviour, potentially contributing to accidents and other injuries.

Unlike earlier studies that typically began with predetermined conditions such as heat exhaustion, heat stroke or heart disease, the researchers used a data-driven approach adapted from genome-wide association studies. By linking clinical information from Chicago’s CAPriCORN data network with climate data according to location and time, the researchers were able to explore a much wider range of potential health effects.

Although the study focused only on Chicago, the researchers said the framework could be applied to other cities, states and countries. It could also be used with different types of health information, including death records and ambulance calls, potentially giving public health officials a more complete picture of how extreme temperatures affect communities.

The findings could also influence how cities prepare for increasingly severe heat. Chicago already uses a Heat Vulnerability Index to help identify neighbourhoods at greater risk and prioritize measures such as air-conditioning upgrades at park fieldhouses. Other proposed strategies include planting more trees, adding shade at bus stops, strengthening heat protections for outdoor workers and ensuring adequate cooling in apartments. Horton said that because extreme heat is associated with numerous health outcomes, reducing people’s exposure to dangerously high temperatures is critical.

More information: Hyojung Jang et al, Identifying heat-related diagnoses in emergency department visits among adults in Chicago: A heat-wide association study, Science Advances. DOI: 10.1126/sciadv.aed3977

Journal information: Science Advances Provided by Northwestern University