Spatial Analysis of Ambient Air Pollution and COVID-19 Death in a Hospitalized Cohort of Confirmed Cases in Southern California

Abstract

Background Recent evidence links ambient air pollution to COVID-19 incidence, severity, and death, but few studies have analyzed individual-level health data with high quality exposure models. Objective We sought to assess whether air pollution exposures led to greater risk of death during or after hospitalization in confirmed COVID-19 cases among patients who were members of the Kaiser Permanente Southern California (KPSC) healthcare system. Methods We used 1 km resolution chemical transport models (CTMs) to estimate ambient concentrations of several common air pollutants, including ozone, nitrogen dioxide, and fine particle matter (PM2.5). We also derived estimates of pollutant exposures less-commonly available in epidemiological studies, including ultra-fine particulate matter (PM0.1), PM chemical species, and PM sources. We used Cox proportional hazards models to assess associations between air pollution exposures and death from COVID-19, while controlling for potential individual and contextual confounders. Results We found significant associations between COVID-19 death and several air pollution exposures, including: PM2.5 mass, PM0.1 mass, PM2.5 nitrates, PM2.5 elemental carbon, PM2.5 on-road diesel, and PM2.5 on-road gasoline. Based on the interquartile (IQR) exposure increment, effect sizes ranged from hazard ratios (HR) = 1.12 for PM2.5 mass and PM2.5 nitrate to HR ~ 1.06-1.07 for other species or source markers. Humidity and temperature in the month of diagnosis were also significant predictors of COVID-19 death and inverse modifiers of the air pollution effects. Conclusion Higher air pollution exposures were associated with a greater risks of COVID-19 death in a cohort of patients hospitalized for COVID-19 in Southern California.