Impact of atmospheric nitrogen dioxide on emergency department visits for asthma in a low air pollution area: a time series and case-crossover study

Objective. To analyze the association between atmospheric levels of nitrogen dioxide (NO2) and the number of visits by adults to an emergency department (ED) for exacerbated asthma in an urban area with low levels of air pollution. Methods. Retrospective ecological time-series study. We quantified ED visits for asthma by consecutive patients over the age of 14 years between 2010 and 2018 (3287 days). The association between the mean atmospheric concentration of NO2 and the number of daily visits to the ED for asthma was analyzed with generalized linear regression analysis (Poisson modeling). The impact of exposure on individual risk was assessed by crossover analysis of case periods. We adjusted for confounding meteorologic variables, potential variability due to seasonal changes was corrected by trend analysis, and 3 time lags were assessed (0, 1, and 3 days). Results. We analyzed 2527 asthma emergencies in 1588 patients (70% female) with a mean (SD) age of 51 (21) years. A significant positive association (relative risk, 1.056, 95% CI, 1.006-1.108; P < .05) between atmospheric NO2 concentration and greater risk of visiting an ED within 3 days was detected. An increase of 10 mu g/m(3) of NO2 accounted for 5.3% of the visits (attributable fraction, 5.30, 95% CI, 0.60-9.75; P < .05). Conclusion. In an urban area with low pollution levels, an elevation in atmospheric NO2 is associated with more hospital ED visits for asthma attacks in adults.