Background: Wildfire smoke exposure has been increasing in the United States in recent years. Previous research has found that wildfire smoke PM2.5 exposure is associated with increased risk of asthma hospitalizations and emergency department visits.
Objectives: In this study, we used the claims of a large insurance provider to estimate the association between wildfire smoke and asthma-related healthcare utilization and prescriptions among children in California.
Methods: Using claims data from a large health plan, we constructed a sample of census tract by day utilization rates for asthma related outcomes and combined this with data measuring PM2.5 associated with wildfire smoke. Our sample consisted of children with commercial health insurance who resided in California between January 2013 and December 2020. We utilized Poisson regression models with linear and binned measures of wildfire smoke exposure and contemporaneous and lagged exposure variables. We account for confounding with multiple fixed effects to control for changes in utilization across time and geography. Wildfire smoke while expected in California may be viewed as quasi-randomly occurring on a single day.
Results: We found that an additional 10 µg/m3 of PM2.5 is associated with increases in inhaler fills (RR 1.041 [95% CI 1.033-1.050], absolute change 1.32 fills per 100,000 children), emergency department visits (RR 1.055 [95% CI 1.032-1.080, absolute change 0.0891 visits per 100,000), and outpatient visits (RR 1.015 [95% CI 1.008-1.023], absolute change 0.50 visits per 100,000). A day with extremely high levels of PM2.5 derived from smoke (above 62.5 µg/m3 ) were associated with large increases in use across: inhaler fills (RR 1.297 [95% CI 1.210-1.391]), emergency department visits (RR 1.597 [95% CI 1.304-1.956]), and outpatient visits (RR 1.097 [95% CI 1.035-1.162]).
Conclusions: In this panel data study, we identified the association between wildfire smoke and increases in asthma-related healthcare utilization for children in California. We find that emergency department visits and inhaler fills were the most responsive to increases in wildfire smoke exposure. This shows that prior studies utilizing data only from emergency department visits only account for half of the direct healthcare impact of wildfire smoke. Inhaler fills being made on the day of the smoke exposure shows that inhalers are not being kept on-hand and are being purchased in response to an increase in symptoms. Public health measures to increase the filling and refilling of inhalers before wildfire smoke could produce increases in welfare for affected children and decrease the load on emergency departments allowing for focus on more severe and acute reactions to wildfire smoke.
