Wildfire Smoke Tied to More Respiratory Hospitalizations in Older Adults

New research shows that high levels of smoke pollution are linked to an increase in hospitalizations for respiratory diseases among older adults.1

“This study, to our knowledge the largest study of smoke PM2.5 and hospitalization to date, found strong evidence of a nonlinear association between daily, county-level smoke PM2.5 and respiratory hospitalizations and weaker but suggestive evidence for cardiovascular hospitalizations,” wrote investigators, led by Sofia L. Vega, AM, from the department of biostatistics at Harvard TH Chan School of Public Health.

This year, 3 wildfires spread across 45 square miles in the highly populated Los Angeles area—the Palisades Fire in Pacific Palisades, the Eaton Fire near Pasadena, and the Hughes Fire in the Castaic area. On January 27, the Los Angeles County Medical Examiner's office reported 29 wildfire-related deaths, according to ABC News.2

Wildfires have surged throughout the West Coast due to climate change, and recently, the East Coast has also faced destructive fires. Grist reported that the Jonas Road Wildfire, which began last Tuesday in the Pine Barrens, is on track to become the worst in New Jersey’s history.3

The fire has spread more than 23 square miles, forced thousands to evacuate, and threatened nuclear waste at a power plant. This wildfire followed other recent ones in the Northeast, including the one in the Hudson Valley and the Catskills last fall and several in the 5 boroughs of New York City.

Wildfires do more than force evacuations and destroy homes or towns—the smoke fumes can extend for thousands of miles and are the predominant source of hazardous fine particulate matter exposure.1

Previous studies have shown the link between wildfire smoke and adverse mortality, respiratory, and cardiovascular outcomes. However, investigators recognized the need for a broader understanding of the health impact of wildfire smoke.

Investigators sought to characterize the associations between exposure to smoke-specific fine particulate matter (PM2.5) and cause-specific hospitalizations among older US adults on the West Coast. They conducted a retrospective cohort study leveraging 2006 to 2016 Medicare inpatient claims data linked to machine learning-derived smoke-specific PM2.5 to evaluate associations between smoke levels and hospitalization rates.

The sample included 10,369,361 older adults aged ≥ 65 years (mean age, 74.7 years) who lived on the West Coast, either Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming. Less than half were female (46.9%), and most were White (80.7%), followed by Hispanic (4.1%) and Black (3.6%). Among the participants, there were 57 million person-months of follow-up, and 4.7 million unscheduled hospitalizations.

The main outcomes were daily county-level rates of unscheduled hospitalization for 13 broad case categories. Investigators analyzed the data between October 2023 and February 2025.

The study showed that smoke PM2.5 concentration-response curves for respiratory and cardiovascular hospitalizations were flat at lower concentrations but had an upward trend at concentrations > 25 μg/m3.

“…hospitalization rates were largely unrelated to smoke PM2.5 at levels less than 20 μg/m3, with a positive association observed at higher concentrations,” the investigators wrote.

On average, daily hospitalizations per 100,000 patients increased by 2.40 (95% confidence interval [CI], 0.17 to 4.63) for respiratory concerns and by 2.61 (95% CI, -0.09 to 5.30) for cardiovascular concerns. These increased daily hospitalizations occurred when smoke PM2.5 concentrations increased the same day or preceding week from 0 to 40 μg/m3. The link between PM2.5 concentrations and increased daily hospitalizations was nonsignificant for patients being admitted for cardiovascular concerns.

“In this cohort study of older adults in the US, exposure to high levels of smoke pollution was associated with an increase in hospitalizations for respiratory diseases,” the investigators concluded. “Findings for cardiovascular disease were not statistically significant but suggest the need for further investigation. This information can be used by both policymakers and clinicians to design policies and guidelines to protect vulnerable older adults from the escalating health threats posed by wildfire smoke.”

References

1. Vega SL, Childs ML, Aggarwal S, Nethery RC. Wildfire Smoke Exposure and Cause-Specific Hospitalization in Older Adults. JAMA Netw Open. 2025;8(4):e257956. doi:10.1001/jamanetworkopen.2025.7956.

2. California fires updates: Death toll in Los Angeles fires rises to 29. ABC News. January 27, 2025. https://abcnews.go.com/US/live-updates/california-wildfires-los-angeles-weather/?id=117613594. Accessed May 1, 2025.

3. The New Jersey wildfire signals new era for Northeast. NJ Spotlight News. May 1, 2025. https://www.njspotlightnews.org/2025/05/the-new-jersey-wildfire-signals-new-era-for-northeast/. Accessed May 1, 2025.