Metropolitan air pollution and the upper and lower airway: chronic rhinosinusitis and asthma outpatient burden

Although evidence has implicated air pollution in both upper and lower airway inflammation, regulatory efforts have primarily emphasized lower-airway outcomes. We characterize the association between ambient pollutant levels and outpatient burden of chronic rhinosinusitis (CRS) and asthma across the US.

We conducted an ecological cohort study of US metropolitan statistical areas (MSAs) between 2007 and 2020. Annual outpatient claims were obtained from the MarketScan database and linked with data from the Environmental Protection Agency (EPA) monitoring network. For each MSA, annual outpatient visits for CRS and asthma were normalized to the number of wellness check visits (CRS-OV, asthma-OV). Daily 365-day rolling averages were calculated for each EPA-monitored pollutants. Mixed-effects models estimated associations with CRS-OV and asthma-OV, and additive pollutant interactions.

Controlling for community health indicators, higher levels of all EPA monitored pollutants predicted increased CRS-OV and asthma-OV. Adjusting for co-pollutant levels, PM2.5 (particles ≤ 2.5um in diameter) and SO2 (gas from fossil fuel combustion) remained independently predictive. Each standard deviation increase in PM2.5 corresponded to 15% and 6% increases in CRS-OV and asthma-OV, while each standard deviation increase in SO2, corresponded to 12% and 10%, respectively. Positive additive interaction between PM2.5 and SO2 was observed for both CRS-OV and asthma-OV.

While EPA-monitored pollutants were broadly associated with outpatient burden, PM2.5 and SO2 emerged as independent and synergistic predictors after co-pollutant adjustment, with stronger associations for CRS compared to asthma. Regulatory focus should extend beyond lower-airway outcomes and include upper-airway morbidity as a critical indicator of pollution-related burden.