Asthma-Associated Emergency Department Visits During the Canadian Wildfire Smoke Episodes — United States, April– August 2023

Results

During days of wildfire smoke occurring during April 30–August 4, 2023, overall observed asthma-associated ED visits^¶¶ were 17% higher than expected among all age groups and HHS regions. Increased (excess) asthma-associated ED visits were detected more commonly on days with a higher percentage of air quality monitors reporting PM_2.5 concentrations indicative of a wildfire smoke day (Supplementary Table, https://stacks.cdc.gov/view/cdc/132183). Specifically, Region 2 (Figure 1), Region 3 (Figure 2), and Region 5 (Figure 3) experienced the most wildfire smoke days with the highest reported PM_2.5 concentrations, the highest percentages of air quality monitors detecting wildfire smoke, and the highest number of excess asthma-associated ED visits.

Region 3 experienced 5 wildfire smoke event days, the highest total amount for any region with more than 1% of air quality monitors reporting AQI ≥101, with a maximum 24-hour average PM_2.5 concentration of 259 μg/m³, and Region 2 and Region 5 experienced a total of 4 wildfire smoke event days, with each reporting a maximum 24-hour average PM_2.5 concentration of 204 μg/m³ and 216 μg/m³, respectively. Within the identified smoke event days, the percentages of air quality monitors reporting wildfire smoke by HHS region ranged from 0.5%–69.0% (Supplementary Table, https://stacks.cdc.gov/view/cdc/132183).

Region 2 experienced the largest increase in asthma-associated ED visits. During June 6–8, higher-than-expected asthma-associated ED visits occurred for all age groups on 2 days, representing 364 excess visits, and among patients aged 5–17 (2 days, 123 excess visits), 18–64 (2 days, 251 excess visits), and ≥65 years (2 days, 12 excess visits) (Figure 1) (Supplementary Table, https://stacks.cdc.gov/view/cdc/132183). On another day (June 29), wildfire smoke was detected at 2.4% of stations, but no days of higher-than-expected asthma-associated ED visits were detected in any age group (Figure 1).

In Region 3, during June 6–8, 1 day of higher-than-expected asthma-associated ED visits was observed among all age groups combined (179 excess visits), and 2 days of higher-than-expected visits were observed among patients aged 18–64 years (128 excess visits). During June 28–29, no higher-than-expected asthma-associated ED visits were observed (Figure 2). In Region 5 during June 27–29, 1 day of higher-than-expected asthma-associated ED visits was observed among all age groups (172 excess visits) and among persons aged 5–17 years (14 excess visits); among persons aged 18–64 years, 2 days of higher than expected asthma-associated ED visits were observed (155 excess visits).

Regions 1, 4, and 9 each experienced 1 day of wildfire smoke and, within these regions, higher-than-expected asthma-associated ED visits were only observed in Region 4. Region 7 experienced 4 days of wildfire smoke, but asthma-associated ED visits were not increased. In Region 8, 3 wildfire smoke days and 1 day of higher-than-expected asthma-associated ED visits occurred among persons aged 18–64 years, representing 18 excess visits. In Region 10, 4 wildfire smoke days with less than 1% of air quality monitors reporting AQI ≥101 had higher-than-expected asthma-associated ED visits representing 14 excess visits among persons aged 18–64 years.