Global, national, and urban burdens of paediatric asthma incidence attributable to ambient NO2 pollution: estimates from global datasets

Background Paediatric asthma incidence is associated with exposure to traffic-related air pollution (TRAP), but the TRAP-attributable burden remains poorly quantified. Nitrogen dioxide (NO2) is a major component and common proxy of TRAP. In this study, we estimated the annual global number of new paediatric asthma cases attributable to NO2 exposure at a resolution sufficient to resolve intra-urban exposure gradients. Methods We obtained 2015 country-specific and age-group-specific asthma incidence rates from the Institute for Health Metrics and Evaluation for 194 countries and 2015 population counts at a spatial resolution of 250 x 250 m from the Global Human Settlement population grid. We used 2010-12 annual average surface NO2 concentrations derived from land-use regression at a resolution of 100 x100 m, and we derived concentration-response functions from relative risk estimates reported in a multinational meta-analysis. We then estimated the NO2-attributable burden of asthma incidence in children aged 1-18 years in 194 countries and 125 major cities at a resolution of 250 x 250. Findings Globally, we estimated that 4.0 million (95% uncertainty interval [UI] 1. 8-5.2) new paediatric asthma cases could be attributable to NO2 pollution annually; 64% of these occur in urban centres. This burden accounts for 13% (6-16) of global incidence. Regionally, the greatest burdens of new asthma cases associated with NO2 exposure per 100 000 children were estimated for Andean Latin America (340 cases per year, 95% UI 150-440), high-income North America (310, 140-400), and high-income Asia Pacific (300, 140-370). Within cities, the greatest burdens of new asthma cases associated with NO2 exposure per 100 000 children were estimated for Lima, Peru (690 cases per year, 95% UI 330-870); Shanghai, China (650, 340-770); and Bogota, Colombia (580, 270-730). Among 125 major cities, the percentage of new asthma cases attributable to NO2 pollution ranged from 5.6% (95% UI 2.4-7.4) in Orlu, Nigeria, to 48% (25-57) in Shanghai, China. This contribution exceeded 20% of new asthma cases in 92 cities. We estimated that about 92% of paediatric asthma incidence attributable to NO2 exposure occurred in areas with annual average NO2 concentrations lower than the WHO guideline of 21 parts per billion. Interpretation Efforts to reduce NO2 exposure could help prevent a substantial portion of new paediatric asthma cases in both developed and developing countries, and especially in urban areas. Traffic emissions should be a target for exposure-mitigation strategies. The adequacy of the WHO guideline for ambient NO2 concentrations might need to be revisited. Copyright (C) 2019 The Author(s). Published by Elsevier Ltd.