Ambient Air Pollution and Risk of Admission Due to Asthma in the Three Largest Urban Agglomerations in Poland: A Time-Stratified, Case-Crossover Study

Ambient air pollution in urban areas may trigger asthma exacerbations. We carried out a time-series analysis of the association between the concentrations of various air pollutants and the risk of hospital admission due to asthma over 7 days from exposure. We used distributed lag nonlinear models to analyze data gathered between 2010 and 2018 in the three largest urban agglomerations in Poland. Overall, there were 31,919 asthma hospitalizations. Over 7 days since exposure, the rate ratio (95%CI) for admission per 10 µg/m(3) was 1.013 (1.002–1.024) for PM(10); 1.014 (1.000–1.028) for PM(2.5); 1.054 (1.031–1.078) for NO(2); and 1.044 for SO(2) (95%CI: 0.986–1.104). For all pollutants, the risk of admission was the greatest on the day of exposure (day 0), decreased below baseline on days 1 and 2, and then increased gradually up to day 6. The proportions (95%CI) of hospitalizations attributable to air pollution were 4.52% (0.80%–8.14%) for PM(10); 3.74% (0.29%–7.11%) for PM(2.5); 16.4% (10.0%–21.8%) for NO(2); and 2.50% (−0.75%–5.36%) for SO(2). In conclusion, PM(2.5), PM(10), NO(2), and SO(2) pollution was associated with an increased risk of hospital admission due to asthma in the three largest urban agglomerations in Poland over nine years.