Wildfire-season Fine Particulate Matter Exposure and Associations with Influenza and Influenza-like-illness Risk in the Western USA.

Authors

Ava Orr, Nisha B Alden, Elizabeth Austin, Zeina Jaffar, Jonathon Knudson, Jon Graham, Christopher T Migliaccio, Curtis Noonan, Shawn Urbanski, Maximilian Wegener, Erin L Landguth

Published in

Environmental health perspectives. Jun 09, 2025. Epub Jun 09, 2025.

Abstract

Influenza remains a significant public health threat, with pandemic potential. Understanding environmental factors influencing virus spread and severity is critical, particularly as wildfires become more frequent and intense. While temperature and humidity's roles in virus seasonality and persistence are well understood, the impacts of air pollution-especially wildfire-specific particulate matter (PM_2.5)-on respiratory infections are less explored.
This study aimed to investigate the association between wildfire PM_2.5 exposure and influenza or influenza-like illness (ILI) incidence. Specifically, we assessed (1) the long-term impact of PM_2.5 exposure during the preceding wildfire season on influenza/ILI risk in the following flu season, and (2) the effects of short-term PM_2.5 exposure during the active flu season.
We utilized ILI and influenza data from state health departments in six Western U.S. states (Arizona, Colorado, Montana, Nevada, Oregon, and Washington) from 2010 to 2019. We applied generalized linear distributed lag models to assess the impact of PM_2.5 exposure during the preceding wildfire season on influenza or ILI risk in the subsequent flu season, as well as the effect of short-term PM_2.5 exposure during the current flu season.
Long-term exposure to wildfire PM_2.5 was associated with increased influenza risk in states with influenza data: Arizona ([Rate Ratio (RR) =1.061 (1.026-1.100)]), Colorado [RR=1.067 (1.056-1.078)], Montana [RR=1.038 (1.013-1.063)], and Oregon [RR=1.049 (1.041-1.057)], per 10 µg/m³ PM_2.5 increase. However, the states with only ILI data did not follow this pattern, revealing no observed effect in Nevada [RR=1.005 (0.920-1.097)] and a negative effect in Washington [RR=0.884 (0.842-0.919)]. Similarly, but to a lesser degree, short-term PM_2.5 exposure effects were noted in states with only influenza data, but not ILI data.
Our findings underscore a positive association between wildfire-specific PM_2.5 and influenza risk in states with influenza data, suggesting a differential effect of PM_2.5 on respiratory infections. This study supports further investigation into causative mechanisms behind these correlations, particularly considering the increasing frequency of wildfires and the resulting air quality impacts. https://doi.org/10.1289/EHP16607.

PMID:
40489657
Bibliographic data and abstract were imported from PubMed on 10 Jun 2025.

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