Asthma exacerbations, meteorological variables, and multipollutant concentrations: Uncovering short-term patterns...

Asthma is a major global health issue, affecting millions of people and contributing significantly to disability-adjusted life years. This study investigates the short-term impacts of outdoor multi-pollutant mixture, pollen, and climate conditions on asthma exacerbations by identifying specific interval concentrations of pollutants that may increase asthma risk. Using a time-stratified case-crossover design combined with Association Rule Mining, a data mining technique, we analyzed data from adult patients who visited the emergency departments in 2019 and 2022 of La Paz University Hospital and Ramón y Cajal University Hospital in Madrid, Spain, and the data on PM₁₀, PM_2.5, O₃, NO₂, NO and SO₂ from 52 monitoring stations. Our findings revealed that specific pollutant concentrations, such as ozone (O₃; 65.3-100 μg/m³) and PM₁₀ (45-50 μg/m³), significantly increased asthma exacerbation risk. These exposures occurred simultaneously or with a time lag of up to three days. Notably, interactions between pollutants, such as O₃ and PM_2.5 or PM_2.5 and pollen, were strongly associated with asthma exacerbations, even when individual pollutant concentrations remained below WHO safety guidelines. Relative risks for these combinations ranged from 1.12 to 1.23, suggesting a cumulative effect. These results underscore the importance of considering pollutant interactions and their time-lagged effects in understanding asthma risks, rather than evaluating pollutants in isolation. Our findings provide mechanistic evidence that future air quality warning systems should account for multi-pollutant exposure patterns, particularly to protect vulnerable populations during critical exposure windows.