Remote wildfire smoke exposure was associated with an 18% increase in cardiopulmonary clinical encounters in Maryland during June 2023, according to a case-only study. The findings documented health impacts extending far beyond the immediate vicinity of wildfires.
In the study, published in JAMA Network Open, investigators analyzed data from the University of Maryland Medical System spanning nine counties, comparing cardiopulmonary clinical encounters during two smoke exposure periods in June 2023 to matched control periods in 2018 and 2019. The study identified 6 "hotspot days" when particulate matter 2.5 micrometers or smaller (PM2.5) levels exceeded the Environmental Protection Agency–National Ambient Air Quality Standard of 35 μg/m3.
During hotspot days, PM2.5 levels in Baltimore City reached mean concentrations of 70.8 μg/m3 (June 6 to 8) and 55.8 μg/m3 (June 28 to 30), representing 9.4-fold and 7.4-fold increases respectively compared with baseline levels of 7.5 μg/m3.
The analysis showed that 25.1% of cardiopulmonary encounters (n = 588/2,339) occurred during hotspot days in 2023 compared with 22.3% (n = 806/3,609) during matched control days (adjusted odds ratio [OR] = 1.18, 95% confidence interval [CI] = 1.03–1.34, P = .02). For cardiac disease specifically, there was a 20% increase in adjusted odds for clinical encounters (adjusted OR = 1.20, 95% CI = 1.01–1.42, P = .04).
The distribution of clinical encounters during hotspot days was:
- 166 (28.2%) in ambulatory settings
- 338 (57.5%) in inpatient settings
- 351 (59.7%) in emergency department settings.
The 2023 cohort included:
- 1,098 female patients (46.9%)
- 710 Black patients (30.4%)
- 1,528 White patients (65.3%)
- Mean age of 68 years.
Significant comorbidities in the 2023 cohort included:
- Systemic hypertension: 40.8%
- Coronary artery disease: 38.4%
- Diabetes: 33.8%
- Congestive heart failure: 35.1%
- Chronic obstructive pulmonary disease: 25.4%
- Obstructive sleep apnea: 12.9%
- Asthma: 9.4%.
The study covered diverse geographic regions, including urban areas (Baltimore and Prince George's Counties) and rural communities (Eastern Shore). The investigators analyzed data from Baltimore, Harford, Anne Arundel, Prince Georges, Charles, Kent, Queen Anne's, Talbot, and Dorchester counties.
The smoke plume trajectory was tracked using Hazard Mapping System data, documenting migration from Western Canadian provinces to Maryland, covering approximately 3,400 km (2,100 miles).
Statistical analysis incorporated adjustments for:
- Age
- Sex
- Race
- Body mass index
- Smoking status
- Overall social vulnerability index.
The proportion of clinical encounters in ambulatory settings during hotspot days was 31.1% (n = 166/533) compared with inpatient settings at 23.2% (n = 338/1,455) and emergency department settings at 22.9% (n = 351/1,536).
The study excluded data from 2020 to 2022 as a result of potential COVID-19 pandemic effects. The investigators used standardized days of the week across years, comparing four complete weeks of June in each year starting with the first Monday and ending with the last Friday of the month.
The research was funded by Montgomery County, Maryland and The University of Maryland Strategic Partnership, with additional support from National Institutes of Health grants 5R01ES033963-02 and T32 AG000262.
Conflict of interest disclosures can be found in the study.