Disruption of outdoor activities caused by wildfire smoke shapes circulation of respiratory pathogens

As climate change accelerates, the frequency and severity of extreme weather events, such as wildfires, are increasing, with profound impacts on human health. While much attention has been paid to the direct health consequences of these events, such as chronic diseases from poor air quality, less is known about how behavioral shifts induced by such events can influence the transmission of infectious diseases. This study investigates how wildfire-induced changes in human behavior during the U.S. West Coast wildfires of 2020 may affect the spread of airborne diseases. Using a mobility data-driven indoor activity index, we find that the wildfire-induced deterioration of air quality led to a substantial increase in indoor activities, fostering conditions conducive to airborne disease transmission. Specifically, counties in Oregon and Washington experienced an average 10.8% and 14.3% increase in indoor activity, respectively, during the wildfire events, with major cities like Portland and Seattle experiencing increases of 11% and 16%, respectively. We quantify these behavioral changes and integrate them into an SIR epidemic model to characterize the increased indoor activity and disease dynamics. The model predicts the greatest impact on diseases with shorter generation times, such as RSV and influenza. Our results show that even a modest increase in indoor mask-wearing (as low as 10%) could significantly reduce the risk of disease spread in these settings, with higher compliance needed for more substantial reductions. As wildfires and other climate-related events become more frequent, integrating behavioral responses into public health policies will be crucial to mitigate the compounded risks of climate change and its secondary health impacts.