Spatiotemporal Interactions of Air Pollution, Airborne Pollen, and Land Cover on Asthma and Allergies Medication Sales: A Population-Level Ecological Study

Introduction The interaction between air pollution and airborne pollen is emerging as a major public health concern, as it may enhance allergic responses and exacerbate asthma at the population level. Available evidence suggests that urban residents experience a higher burden of respiratory allergies than rural populations, potentially due to the combined effects of chemical air pollutants and pollen exposure. Air pollutants may modify pollen characteristics, increase allergen release and potency, and promote airway inflammation, thereby amplifying allergic sensitization and respiratory symptoms. Aims For the first time, the relationship between air pollution, pollen, and asthma and allergies is investigated by simultaneously factoring in spatiotemporal land cover data (urban, agricultural, and forest spaces). Methods We utilized descriptive statistics, Principal Component Analysis (PCA), Hierarchical Cluster Analysis (HCA), and spatial analysis to understand the relationship of birch, grass and all taxons count, NO2 and PM2.5 concentrations (micro grams/m3) and land cover type (urban/rural, agriculture, forest) in Bordeaux, Clermont, Marseille, Nancy, Paris, Poitiers, Reims and Strasbourg using prescribed and over the count sales data for asthma (R03) and allergies (R06), from a representative sample of pharmacies (n=12,000), in 2013. Results In 2013, the 8 cities saw total sales of 9,684,577 R03 and 12,344,102 R06 medications, with sales peaks coinciding with high pollen and air pollution. A spatiotemporal and land cover analysis revealed that relationships between these variables are highly context-dependent. For instance, higher R06 sales clustered in areas with medium pollen (taxon deciles 3 to 4, grass 4 to 5, birch 6 to 7), high pollution ("NO" _2 deciles 8 to 10, "PM" _2.5 5 and 8 to 10, "PM" _10 3, 7, 9 to10), high agricultural land, and low forest/urban space. Conversely, some associations did not vary by location, suggesting external influencing factors. Conclusions Our data raise evidence that pollen and air pollution can act synergistically according to the land cover characteristics. Other investigations are needed to confirm the relationship.