Wildfire-Led Indoor Activity May Raise Flu Transmission Risk

TOPLINE:

Researchers found that wildfire-induced deterioration of air quality led to substantial increases in indoor activities, creating a cascade effect that could dramatically increase the spread of respiratory pathogens such as the influenza virus.

METHODOLOGY:

• The 2020 West Coast wildfires highlighted how extreme weather events coupled with deteriorating air quality can influence disease transmission through changes in human behavior, particularly increased indoor activity.
• Researchers performed a modeling analysis to quantify behavioral changes induced by wildfires and assess their impact on the transmission dynamics of respiratory viruses.
• During the peak wildfire period, mobile phone data were used to track weekly visits to indoor locations (such as schools, hospitals, and grocery stores) vs outdoor locations (such as parks and cemeteries), comparing counties with an air quality index > 150 (most affected counties) with those with an index < 100 (unaffected counties).
• Using mathematical simulations, researchers assessed how these behavioral shifts (from outdoor to indoor activities) and indoor mask-wearing would influence the spread of faster and slower spreading viruses.

TAKEAWAY:

• In counties with elevated air quality index from wildfire smoke, sustained increases in indoor activity were reported — 10.8% in Washington, 14.3% in Oregon, with peak increase of 16% in Seattle and 11% in Portland. However, unaffected counties reported no change.
• Diseases with shorter generation times (influenza and SARS-CoV-2 ) showed a twofold increase in peak incidence in affected vs unaffected areas, attributed to increased indoor activity; this effect declined with longer generation time.
• Even with 50% population having immunity from past infection or vaccination, wildfire-affected counties showed higher incidence of influenza, suggesting that wildfire-driven behavior changes can still boost disease transmission.
• The study demonstrated that a modest 10% increase in mask usage notably reduced disease spread; however, substantial protection, required mask compliance rates of around 50%.

IN PRACTICE:

“By revealing how behavioral shifts induced by wildfires can elevate disease spread, our study advocates for the inclusion of behavioral responses in public health strategies. As climate change continues to alter our environment, it is crucial for public health interventions to evolve accordingly, equipping us to tackle the multifaceted and interconnected risks of a warming world,” the authors wrote.

SOURCE:

This study was led by Beatriz Arregui-García, Instituto de Física Interdisciplinar y Sistemas Complejos, Palma de Mallorca, Spain. It was published online on June 18, 2025, in PLOS Climate.

LIMITATIONS:

This study focused on a single wildfire season in the US, possibly limiting the generalizability of the findings. The analysis relied only on the ratio of indoor-to-outdoor activities and did not account for indoor activities at home. The study did not incorporate public health data on infection rates, limiting a direct correlation between behavioral changes and disease outcomes.

DISCLOSURES:

This study was supported by the Fritz Family Fellowship. One author disclosed receiving salary support from the fellowship program. Other authors declared having no competing interests.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.