Impacts of ambient air quality on acute asthma hospital admissions during the COVID-19 pandemic in Oxford City, UK: a time-series study.

<h4>Objectives</h4>The study aims to investigate the short-term associations between exposure to ambient air pollution (nitrogen dioxide (NO₂), particulate matter pollution-particles with diameter<2.5 µm (PM_2.5) and PM₁₀) and incidence of asthma hospital admissions among adults, in Oxford, UK.<h4>Design</h4>Retrospective time-series study.<h4>Setting</h4>Oxford City (postcode areas OX1-OX4), UK.<h4>Participants</h4>Adult population living within the postcode areas OX1-OX4 in Oxford, UK from 1 January 2015 to 31 December 2021.<h4>Primary and secondary outcome measures</h4>Hourly NO₂, PM_2.5 and PM₁₀ concentrations and meteorological data for the period 1 January 2015 to 31 December 2020 were analysed and used as exposures. We used Poisson linear regression analysis to identify independent associations between air pollutant concentrations and asthma admissions rate among the adult study population, using both single (NO₂, PM_2.5, PM₁₀) and multipollutant (NO₂ and PM_2.5, NO₂ and PM₁₀) models, where they adjustment for temperature and relative humidity.<h4>Results</h4>The overall 5-year average asthma admissions rate was 78 per 100 000 population during the study period. The annual average rate decreased to 46 per 100 000 population during 2020 (incidence rate ratio 0.58, 95% CI 0.42 to 0.81, p<0.001) compared to the prepandemic years (2015-2019). In single-pollutant analysis, we observed a significantly increased risk of asthma admission associated with each 1 μg/m³ increase in monthly concentrations of NO₂ 4% (95% CI 1.009% to 1.072%), PM_2.5 3% (95% CI 1.006% to 1.052%) and PM₁₀ 1.8% (95% CI 0.999% to 1.038%). However, in the multipollutant regression model, the effect of each individual pollutant was attenuated.<h4>Conclusions</h4>Ambient NO₂ and PM_2.5 air pollution exposure increased the risk of asthma admissions in this urban setting. Improvements in air quality during COVID-19 lockdown periods may have contributed to a substantially reduced acute asthma disease burden. Large-scale measures to improve air quality have potential to protect vulnerable people living with chronic asthma in urban areas.