EXTREME heat was linked to higher asthma emergency department visits among adults and children in Baltimore, especially after hot nights.
A spatially detailed analysis of asthma related emergency department visits in Baltimore, Maryland, found that extreme heat and asthma exacerbations were significantly associated across both pediatric and adult populations. The study included 819 adult and 695 pediatric asthma exacerbations from 2016 to 2022, combining geocoded electronic health records with air temperature measurements at multiple spatial resolutions.
The findings suggest that the way heat exposure is defined and measured can substantially shape clinical and public health conclusions. When temperature estimates were assessed at the census block group or census tract level, nighttime heat wave definitions based on elevated minimum temperatures showed strong associations with asthma exacerbations.
Nighttime Heat Signals Local Asthma Risk
Nighttime heat emerged as a key signal when investigators used more granular temperature data. These associations were observed in both age groups and were more pronounced in socially vulnerable areas, where neighborhood level heat exposure and asthma burden may overlap.
Baltimore’s urban heat island effect is particularly relevant at night, when built environments can retain heat and prevent temperatures from dropping. The study indicates that minimum temperature metrics may capture a clinically important dimension of heat exposure that daytime focused systems can miss.
By contrast, heat wave definitions derived from the city’s primary National Weather Service synoptic weather station showed associations between asthma and daytime heat extremes. This difference suggests that coarse weather station data may detect broader daytime hazards but fail to identify localized nighttime risk.
Heat Wave Definitions Shape Public Health Signals
The study tested 11 heat wave definitions from recent literature, including relative percentile based thresholds and fixed absolute temperature thresholds. Extreme heat and asthma associations varied depending on whether heat was defined by daytime, nighttime, or average temperature, as well as the spatial resolution used.
Notably, the extreme heat event definition used by Baltimore City’s Code Red system was not significantly associated with asthma exacerbations. The authors noted that alert systems relying on daytime heat indices may underestimate the full extent of heat exposure, particularly in neighborhoods affected by sustained nighttime temperatures.
These findings support greater attention to high resolution temperature data, geocoded health records, and nighttime heat metrics when evaluating asthma risk in urban environments. For clinicians and public health teams, the results reinforce that extreme heat and asthma risk may be most visible when exposure is measured at the neighborhood level.
Reference
Corpuz B et al. Impact of Extreme Heat on Emergency Department Admissions for Childhood and Adult Asthma: An Evaluation of Earth Observations and Heat Wave Definitions. GeoHealth. 2026;10(5):e2025GH001501.
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