Alari, AnnaRanzani, OtavioOlmos, SergioMilà, CarlesRico, AlexBallester, JoanBasagaña Flores, XavierDadvand, PayamDuarte Salles, Talita, 1985-Nieuwenhuijsen, Mark J.Vivanco Hidalgo, Rosa MaríaTonne, Cathryn2024-09-032024Alari A, Ranzani O, Olmos S, Milà C, Rico A, Ballester J, et al. Short-term exposure to air pollution and hospital admission after COVID-19 in Catalonia: the COVAIR-CAT study. Int J Epidemiol. 2024 Feb 14;53(2):dyae041. DOI: 10.1093/ije/dyae0410300-5771http://hdl.handle.net/10230/60993Background: A growing body of evidence has reported positive associations between long-term exposure to air pollution and poor COVID-19 outcomes. Inconsistent findings have been reported for short-term air pollution, mostly from ecological study designs. Using individual-level data, we studied the association between short-term variation in air pollutants [nitrogen dioxide (NO2), particulate matter with a diameter of <2.5 µm (PM2.5) and a diameter of <10 µm (PM10) and ozone (O3)] and hospital admission among individuals diagnosed with COVID-19. Methods: The COVAIR-CAT (Air pollution in relation to COVID-19 morbidity and mortality: a large population-based cohort study in Catalonia, Spain) cohort is a large population-based cohort in Catalonia, Spain including 240 902 individuals diagnosed with COVID-19 in the primary care system from 1 March until 31 December 2020. Our outcome was hospitalization within 30 days of COVID-19 diagnosis. We used individual residential address to assign daily air-pollution exposure, estimated using machine-learning methods for spatiotemporal prediction. For each pandemic wave, we fitted Cox proportional-hazards models accounting for non-linear-distributed lagged exposure over the previous 7 days. Results: Results differed considerably by pandemic wave. During the second wave, an interquartile-range increase in cumulative weekly exposure to air pollution (lag0_7) was associated with a 12% increase (95% CI: 4% to 20%) in COVID-19 hospitalizations for NO2, 8% (95% CI: 1% to 16%) for PM2.5 and 9% (95% CI: 3% to 15%) for PM10. We observed consistent positive associations for same-day (lag0) exposure, whereas lag-specific associations beyond lag0 were generally not statistically significant. Conclusions: Our study suggests positive associations between NO2, PM2.5 and PM10 and hospitalization risk among individuals diagnosed with COVID-19 during the second wave. Cumulative hazard ratios were largely driven by exposure on the same day as hospitalization.application/pdfeng© Oxford University Press. This is a pre-copyedited, author-produced version of an article accepted for publication in International journal of epidemiology following peer review. The version of record Alari A, Ranzani O, Olmos S, Milà C, Rico A, Ballester J, et al. Short-term exposure to air pollution and hospital admission after COVID-19 in Catalonia: the COVAIR-CAT study. Int J Epidemiol. 2024 Feb 14;53(2):dyae041. DOI: 10.1093/ije/dyae041 is available online at: http://dx.doi.org/10.1093/ije/dyae041info:eu-repo/semantics/articlehttp://dx.doi.org/10.1093/ije/dyae041Air pollutionCOVID-19Distributed lag non-linear modelsHospitalizationPopulation-based cohortTime-to-event analysisinfo:eu-repo/semantics/embargoedAccess