Late Breaking Abstract - Pre- and postnatal air pollution’s association with infant microbiome and respiratory symptoms

<bold>Background:</bold> Little is known about the mediating role of nasal microbiome on the association between pre- and postnatal air pollution and subsequent respiratory morbidity in infancy. <bold>Aims:</bold> We aimed to examine the impact of air pollution on nasal microbiome and respiratory symptoms in infancy, and if microbiome mediates the association between air pollution and symptoms. <bold>Methods:</bold> Nasal swabs from 270 infants from the prospective Basel-Bern Infant Lung Development (BILD) cohort were analysed by 16S ribosomal RNA gene sequencing. We investigated the effect of nitrogen dioxide (NO2) and particulate matter ≤ 2.5 µm (PM2.5) during pregnancy and the first 4–6 weeks of life on microbiome at 4–6 weeks and on weekly assessed respiratory symptoms during the first year of life. Hierarchical clustering was performed to characterize microbiome profiles and generalized structural equation modelling for mediation analysis. <bold>Results:</bold> We identified two distinct microbiome clusters, characterized by high Corynebacterium/Dolosigranulum and high Staphylococcus/Streptococcus abundance, respectively. Increased pre- and postnatal air pollution exposure was associated with Staphylococcus/Streptococcus cluster (e.g., per 10 µg/m3 increase in prenatal NO2: odds ratio 1.63, 95% confidence interval 1.12;2.38, padj=0.022). Pre- and postnatal PM2.5 increased the risk for severe respiratory symptoms. This association was not mediated by the nasal microbiome. <bold>Conclusion:</bold> Pre- and postnatal air pollution was associated with microbiome and respiratory symptoms in infancy. The microbiome did not mediate the effect of air pollution on respiratory symptoms, which may indicate that other mechanisms are more relevant at this age.