Extreme Heat Tied to Dermatologic Acute Care Diagnoses

Key Takeaways

• Among adults in Chicago emergency department and urgent-care settings, at the warm-season 95th-percentile temperature relative to diagnosis-specific minimum risk temperatures, multiple dermatologic and pressure-related diagnoses showed elevated cumulative odds of acute-care visits over lags 0 to 3 days.
• The heat-associated diagnosis spectrum also included fluid-balance and renal disorders, varicose veins of the lower extremities, multiple sclerosis, a cannabinoid-related mental and behavioral disorder, and injuries and external causes.
• The two-stage analysis narrowed the initial heat-associated signal to a smaller set of diagnoses meeting the stage 2 numerical reporting criteria.
• The authors said that examining the full diagnostic spectrum improved characterization of heat-associated morbidity in acute-care settings.

During periods of extreme heat, acute-care morbidity can extend beyond visits coded as heat illness alone. Patients presenting during or shortly after extreme heat may have diagnoses extending beyond explicitly coded heat illness, including renal and fluid-balance disorders, dermatologic conditions, neurologic or behavioral diagnoses, and injuries. Examining only explicit heat-illness codes may therefore provide an incomplete picture of heat-associated acute-care morbidity. In Chicago adults, this raised a broader question about which diagnoses move with extreme heat when clinicians look beyond explicit heat illness codes.

Investigators conducted a study of acute care diagnoses during extreme heat using routine emergency department and urgent-care encounters among adults in Chicago, Illinois, across four health care systems from 2011 to 2023. The dataset included 916,904 acute-care visits among 372,140 adults. Researchers used a two-stage analysis: first applying quasi-Poisson regression to screen diagnosis codes associated with heat, and then using distributed lag nonlinear models in a time-stratified case-crossover design to characterize how those associations related to exposure intensity and short-term timing.

Stage 1 retained 44 diagnosis codes, and 33 diagnoses met the stage 2 numerical reporting criteria. During extreme heat, investigators observed elevated cumulative odds over lags 0 to 3 days. The reported diagnosis groups extended beyond explicit heat illness coding and included dermatologic and pressure-related conditions; fluid-balance and renal disorders; varicose veins of the lower extremities; multiple sclerosis; a cannabinoid-related mental and behavioral disorder; and multiple injuries and external causes.

These findings describe observational associations rather than causation, and the reported setting was adult acute-care settings in Chicago across four health care systems, which limits how directly the pattern can be applied to other populations or care environments. The findings also require replication because both analytic stages used the same underlying cohort without external validation, and several associations were sensitive to screening criteria and seasonal definition. When analyses were restricted to June through August, only volume depletion remained in the stage 2 reporting set, supporting cautious interpretation of several injury and external-cause findings as exploratory warm-season signals.

Heat-associated acute-care morbidity appeared to extend beyond explicit heat illness coding, with dermatologic and pressure-related presentations included in a broader clinical spectrum. The authors said that analyzing the full diagnostic spectrum of acute-care services improved characterization of heat-associated morbidity in acute-care settings.

Clinician Questions

Which patients and acute-care settings were included in the Chicago heat-wide association study?

The analysis covered 916,904 acute-care visits among 372,140 adults in Chicago across four health care systems from 2011 to 2023, and the encounters included emergency department and urgent-care visits. The reported context was adult acute-care settings in Chicago rather than pediatric, inpatient, or nonacute outpatient populations.

What does the lag 0 to 3 days finding mean for heat-associated acute-care diagnoses?

The study reports elevated cumulative odds when effects were summed across lags 0 to 3 days for the named diagnosis groups.

What diagnoses were captured when investigators looked beyond explicit heat illness codes in Chicago adults?

The broader diagnostic spectrum included dermatologic and pressure-related conditions along with fluid-balance and renal disorders, varicose veins of the lower extremities, multiple sclerosis, a cannabinoid-related mental and behavioral disorder, and multiple injuries and external causes. That spectrum reflects diagnoses identified when investigators screened across acute-care codes rather than relying only on explicit heat illness labels.