Ambient Anthropogenic Carbons and Pediatric Respiratory Infections: A Case-Crossover Analysis in the Megacity Beijing.

Carbon loading in airway cells has shown to worsen function of antimicrobial peptides, permitting increased survival of pathogens in the respiratory tract; however, data on the impacts of carbon particles on childhood acute respiratory infection (ARI) is limited. We assembled daily health data on outpatient visits for ARI (bronchitis, pneumonia, and total upper respiratory infection [TURI]) in children aged 0-14 years between 2015 and 2019 in Beijing, China. Anthropogenic carbons, including black carbon (BC) and its emission sources, and wood smoke particles (delta carbon, ultra-violet absorbing particulate matter, and brown carbon) were continuously monitored. Using a time-stratified case-crossover approach, conditional logistic regression was performed to derive risk estimates for each outcome. A total of 856,899 children were included, and a wide range of daily carbon particle concentrations was observed, with large variations for BC (0.36-20.44) and delta carbon (0.48-57.66 μg/m). Exposure to these particles were independently associated with ARI, with nearly linear exposure-response relationships. Interquartile range increases in concentrations of BC and delta carbon over prior 0-8 days, we observed elevation of the odd ratio of bronchitis by 1.201 (95% confidence interval, 1.180, 1.221) and 1.048 (95% CI, 1.039, 1.057), respectively. Stronger association was observed for BC from traffic sources, which increased the odd ratio of bronchitis by 1.298 (95% CI, 1.273, 1.324). Carbon particles were also associated with elevated risks of pneumonia and TURI, and subgroup analyses indicated greater risks among children older than 6 years. Our findings suggested that anthropogenic carbons in metropolitan areas may pose a significant threat to clinical manifestations of respiratory infections in vulnerable populations.