High Level of Nitrogen Dioxide in Ambient Air Increased Incidence of Influenza in Children: An Observational Study in China

Abstract

Background: The roles of air pollutants including nitrogen dioxide (NO2), sulfur dioxide (SO2), carbon monoxide (CO) and ozone (O3) in influenza incidence at nationwide level of China remained obscure. Methods: Data from two complementary nation-wide influenza surveillance systems were applied to examine the association between air pollutants and influenza incidences. Spatial epidemiological analyses were performed on both air pollutants and influenza incidences in 31 provinces of mainland China. Cities with consistent data patterns between the two surveillance systems were chosen to examine the effects of pollutants on monthly influenza incidences using generalized estimating equations (GEE) and on daily incidence using the distributed lag non-linear model (DLNM). Results: Out of five common air pollutants (NO2, SO2, O3, CO, PM2.5), the concentration of NO2 was found spatially correlated with annual average influenza positive rates at province level (Pearson’s correlation coefficient=0.69, P<0.001). Based on data from 134 cities, NO2 and SO2 were found positively associated with monthly influenza incidences with estimated RRs of 1.22 and 1.09, respectively. The RRs increased to 1.45 and 1.13 among children younger than 18 years. NO2 is the only pollutant that showed robust positive association with daily influenza incidence in 12 of the 18 cities with adequate daily incidence data. The positive association was found in children under 18 years but not in adults. Interpretation: A higher NO2 concentration in ambient air was associated with an increased incidence of influenza across a wide geographic range in China with more vulnerable impact in Children. These findings reflect the need for annual vaccination campaign among children and their parents as well as air pollution control in densely populated urban areas. Funding Information: The National Natural Science Foundation of China; The China Mega-Project on Infectious Disease Prevention; The Key Research and Development Program of China; The US National Institutes of Health grant. Declaration of Interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf and declare: no support from any organization for the submitted work; no financial relationships with any organizations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work. Ethics Approval Statement: The current study was approved by Beijing Institute of Microbiology and Epidemiology in accordance with the medical research regulations of China.