Traffic-related air pollution and the local burden of childhood asthma in Bradford, UK

Asthma is a burdensome disease which is often cited as the most common chronic disease in childhood. Traffic-related air pollution (TRAP) may be an important exposure in the development of childhood asthma. However, the burden of childhood asthma attributable to TRAP is poorly documented. Using a land-use regression (LUR) model, we estimated the childhood (birth-18 years old) population exposure to the following three air pollutants in Bradford, UK: Particulate Matter equal or less than 2.5 micrometers in diameter (PM2.5), Particulate Matter equal or less than 10 micrometers in diameter (PM10) and Black Carbon (BC). We assigned exposures at the lowest census tract level: the ‘output area’. We extracted national and local childhood asthma incidence rates from the literature and used meta-analytic exposure-response functions to calculate the relative risk, population attributable fraction of childhood asthma in association with each pollutant and the number of childhood asthma cases attributable to each pollutant. We investigated the impacts of reducing air pollutants at each output area to comply with the World Health Organization’s (WHO) air quality guidelines. At the output area level, the annual mean PM2.5, PM10 and BC concentrations were 10.40 µg/m3, 16.63 µg/m3 and 1.07 × 10−5 m−1, respectively. Depending on the pollutant, the estimated number of attributable childhood asthma cases varied between 279 and 612 annually, representing between 15% and 33% of all cases in the city. Between 7% and 12% of annual childhood asthma cases were specifically attributable to TRAP. Compliance with the WHO air quality guidelines prevented up to 29 cases. Using national versus local baseline childhood asthma incidence rates with differing underlying asthma definitions resulted in up to 322% as many attributable cases. Air pollution is estimated to cause a large, but preventable, childhood asthma burden. The burden of disease varied depending on the pollutant selected.