IMPORTANCE

The escalating intensity of wildfires in the western US is increasing exposure to smoke pollution. Previous studies of wildfire smoke and health have primarily focused on mortality and respiratory and cardiovascular events, with limited research on broader health impacts or on the shape of concentration-response curves.

OBJECTIVE

To characterize the associations between exposure to smoke-specific fine particulate matter (PM2.5) and cause-specific hospitalizations among older adults in the western US.

DESIGN, SETTING, AND PARTICIPANTS: This retrospective cohort study used Medicare inpatient claims data from 2006 to 2016 linked with machine learning-derived smoke-specific PM2.5 to assess associations between smoke PM2.5 and hospitalization rates. Participants included Medicare beneficiaries aged 65 years or older who lived in a western US state (ie, Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, or Wyoming). Analyses were conducted from October 2023 to February 2025.

EXPOSURES

Daily county-level smoke-specific PM2.5 concentrations were estimated from machine learning models trained on monitor and satellite data.

MAIN OUTCOMES AND MEASURES

Daily county-level rates of unscheduled hospitalization for each of 13 broad cause categories. To characterize the association between each cause of hospitalization and smoke PM2.5, distributed lag models were fitted with hospitalization rates modeled as a function of same-day smoke PM2.5 exposure and exposures on each day of the preceding week, using splines on exposure to allow for nonlinearity.

RESULTS

The study included 10 369 361 individuals (mean [SD] age, 74.7 [7.9] years; 4 862 826 male [46.9%]; 5 506 535 female [53.1%]; 373 252 Black [3.6%]; 420 577 Hispanic [4.1%]; and 8 365 607 White [80.7%]), 57 million person-months of follow-up, and 4.7 million unscheduled hospitalizations. Smoke PM2.5 concentration-response curves for respiratory hospitalizations and cardiovascular hospitalizations were flat at lower concentrations but showed increasing trends at concentrations above 25 μg/m3. On average, daily hospitalizations (per 100 000) increased by 2.40 (95% CI, 0.17 to 4.63) for respiratory concerns when increasing same-day and preceding week smoke PM2.5 concentrations from 0 to 40 μg/m3; hospitalizations for cardiovascular concerns increased by 2.61 (95% CI, -0.09 to 5.30), a difference that was not statistically significant. No associations were observed for other causes of hospitalization.

CONCLUSIONS AND RELEVANCE

In this cohort study, exposure to high levels of smoke pollution was associated with an increase in hospitalizations for respiratory diseases. These findings underscore the need for interventions to mitigate the health impacts of wildfire smoke exposure.