The association of increased pre- and postnatal NO 2 and PM 2.5 exposure with the infant nasal microbiome composition and respiratory symptoms

Little is known about the mediating role of nasal microbiome on the association between pre- and postnatal air pollution exposure and subsequent respiratory morbidity in infancy. We aimed to examine the impact of air pollution on microbiome and respiratory symptoms, and whether microbiome mediates the association between air pollution and symptoms. Nasal swabs from 270 infants in the prospective Basel-Bern Infant Lung Development cohort were analyzed by 16S ribosomal RNA gene sequencing. We investigated the association of pre- and postnatal nitrogen dioxide (NO 2 ) and particulate matter ≤2.5 μm (PM 2.5 ) with microbiome at 4–6 weeks and with respiratory symptoms during the first year of life. Hierarchical clustering and generalized structural equation modeling were used. Mean prenatal air pollution levels were 21.54 μg/m 3 (NO 2 ) and 13.84 μg/m 3 (PM 2.5 ) (WHO guideline limits: NO 2 : 40 μg/m 3 (2005), 10 μg/m 3 (2021); PM 2.5 : 10 μg/m 3 (2005), 5 μg/m 3 (2021)). We identified two distinct microbiome clusters, characterized by high Corynebacterium / Dolosigranulum and high Staphylococcus abundance. Higher pre- and postnatal air pollution exposure was associated with Staphylococcus cluster (e.g., per 10 μg/m 3 increase of prenatal NO 2 : odds ratio 1.58, 95% confidence interval 1.08; 2.29, p adj  = 0.034). Pre- and postnatal PM 2.5 was associated with increased risk of severe respiratory symptoms. This association was not mediated by nasal microbiome. Pre- and postnatal air pollution was associated with microbiome and respiratory symptoms in infancy. The microbiome did not mediate the association of air pollution with respiratory symptoms, which may indicate that other mechanisms are more relevant at this age.