Exposure to outdoor air pollution and risk of hospitalization for bronchiolitis in an urban environment: A 9-year observational study

Background: Outdoor air pollution is supposed to influence the course of bronchiolitis, but the evidence is limited. The present study aimed at evaluating the role of outdoor air pollutants on hospitalization for bronchiolitis. Methods: Infants aged ≤12 months referred for bronchiolitis to our Pediatric Emergency Department in Bologna, Italy, from 1 October 2011 to 16 March 2020 (nine epidemic seasons) were retrospectively included. Daily concentrations of benzene (C6H6), nitrogen dioxide (NO2), particulate matter ≤2.5 μm (PM2.5), and ≤10 μm (PM10), and the mean values of individual patient exposure in the week and the 4 weeks before hospital access were calculated. The association between air pollutants exposure and hospitalization was evaluated through logistic regression analysis. Results: A total of 2902 patients were enrolled (59.9% males; 38.7% hospitalized). Exposure to PM2.5 in the 4 weeks preceding bronchiolitis was identified as the main parameter significantly driving the risk of hospitalization (odds ratio [95% confidence interval]: 1.055 [1.010–1.102]). After stratifying by season, higher values of other outdoor air pollutants were found to significantly affect hospitalization: 4-week exposure to C6H6 (Season 2011–2012, 4.090 [1.184–14.130]) and PM2.5 (Season 2017–2018, 1.282 [1.032–1.593]), and 1-week exposure to C6H6 (Season 2012–2013, 6.193 [1.552–24.710]), NO2 (Season 2013–2014, 1.064 [1.009–1.122]), PM2.5 (Season 2013–2014, 1.080 [1.023–1.141]), and PM10 (Season 2018–2019, 1.102 [0.991–1.225]). Conclusion: High levels of PM2.5, C6H6, NO2, and PM10 may increase the risk of hospitalization in children affected by bronchiolitis. Open-air exposure of infants during rush hours and in the most polluted areas should be avoided.