An integrated approach identifying seasonal variation in allergenic grass pollen in southern Australia

During the southern hemisphere spring, Melbourne, Australia experiences a pronounced increase in asthma-related hospital admissions that coincides with the grass pollen season. This period is also associated with heightened risk of epidemic thunderstorm asthma (ETSA), representing a significant public health concern. Accurate identification of the grass pollen taxa contributing to aeroallergen exposure, and understanding their temporal dynamics, is critical for effective clinical management of seasonal allergic disease and improved prediction of ETSA risk. We characterised airborne grass pollen diversity and allergen abundance in Melbourne using an integrated monitoring framework combining manual pollen counts, allergen immunoassays, DNA metabarcoding, and targeted quantitative PCR (qPCR) over two consecutive grass pollen seasons (2022-2023). Internal transcribed sequence 2 (ITS2) metabarcoding showed that airborne grass pollen was dominated by temperate Pooideae taxa, with Lolium (ryegrasses), Holcus (velvet grasses), Anthoxanthum (vernal grasses), and Agrostis (bent grass) comprising the majority of sequences. Assessing seasonal fluctuations in pollen-derived gDNA from these four taxa identified Lolium as having a significant association with weekly grass pollen levels and group 5 allergen concentrations. This finding confirms the view that Lolium is the most abundant type of grass pollen in Melbourne's air and the main contributor to seasonal allergies. Integrating traditional aerobiological monitoring with molecular and immunological techniques enabled identification of grasses that contribute clinically relevant aeroallergens and their temporal dynamics. This transferable framework improves assessment of grass pollen exposure, supports more informed clinical and public health decision-making, and provides a foundation for detecting climate-driven shifts in grass aeroallergen composition relevant to future ETSA risk and respiratory health planning.