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Extreme but discrete fine particle <2.5μm (PM_2.5) exposure is associated with higher prevalence of respiratory symptoms. It was unknown whether these effects abate, persist, or worsen over time, nor whether they are exacerbated by COVID-19.

We analysed longitudinal survey data from a cohort residing near a 2014 coalmine fire in regional Australia. A 2016/2017 survey included 4,056 participants, of whom 612 were followed-up in 2022. Items included questions on respiratory symptoms, history of COVID-19, and time-location diaries that were combined with geospatial and temporal models of fire-related PM_2.5. Associations were examined using logistic and mixed-effects logistic regressions.

PM_2.5 exposure predicted higher prevalence of chronic cough and current wheeze 2-3 years post-fire. At the 2022 follow-up, PM_2.5 exposure was associated with worsening prevalence of chronic cough and possibly current wheeze. While there were no detectable interaction effects between PM_2.5 and COVID-19, PM_2.5 exposure was associated with additional respiratory symptoms among participants who reported a history of COVID-19.

Short-term but extreme PM_2.5 may increase the long-term prevalence of chronic cough, while COVID-19 may exacerbate the effect on additional respiratory symptoms.