The influence of air pollutants on the risk of emergency department presentations of infants with bronchiolitis in an European air quality hotspot

Background: Acute bronchiolitis is the leading cause of hospitalization in infants, and air pollutants represent a risk factor for its development. This work aims to investigate the role of air pollution, considering conventional and nonconventional indicators, in the development of bronchiolitis in three urban areas in the Po Valley, Northern Italy. Methods: This multicentric, observational, retrospective, cohort study included infants under 12 months who were referred to the Pediatric Emergency Department of Bologna, Belluno, and Biella and diagnosed with bronchiolitis from 2016 to 2019. Data on daily ground-level mass concentrations of particulate matter (PM10 and PM2.5) and gaseous pollutants in the three areas, and additionally of organic carbon (OC) and elemental carbon (EC) in Bologna, were retrieved and assessed for possible relationships with the occurrence of bronchiolitis. Results: A total of 1316 patients were enrolled. All conventional air quality indicators (NO2, PM10, and PM2.5) showed statistically significant associations with the occurrence of referrals due to bronchiolitis. The highest impacts were observed for OC and EC, the carbonaceous components of PM, which were only measured in Bologna. Considering the conventional indicators, the strongest associations were found between 4-week moving average concentrations and weekly hospital admission, and the strongest associations were found considering NO2 and PM2.5. Conclusion: This study indicates that medium-term exposure to higher levels of air pollution increases the risk of the development of bronchiolitis. In particular, the best association results between bronchiolitis admissions and the exposure to the carbonaceous fraction of PM2.5.