Inhalation of grass pollen can result in acute exacerbation of asthma, prompting questions about how grass pollen reaches metropolitan areas. We establish typical atmospheric Poaceae (grass) pollen concentrations recorded at two pollen samplers within the Sydney basin in eastern Australia and analyse their correlation with each other and meteorological variables. We determine the effect of synoptic and regional airflow on Poaceae pollen transport during a period of extreme (≥ 100 grains m−3 air) concentration and characterise the meteorology. Finally, we tested the hypothesis that most Poaceae pollen captured by the pollen samplers originated from local sources. Fifteen months of daily pollen data, three days of hourly atmospheric Poaceae pollen concentrations and fifteen months of hourly meteorology from two locations within the Sydney basin were used. Weather Research Forecasting (WRF), Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) modelling and conditional bivariate probability functions (CBPF) were used to assess Poaceae pollen transport. Most Poaceae pollen collected was estimated to be from local sources under low wind speeds. Extreme daily Poaceae pollen concentrations were rare, and there was no strong evidence to support long-distance Poaceae pollen transport into the Sydney basin or across the greater Sydney metropolitan area. Daily average pollen concentrations mask sudden increases in atmospheric Poaceae pollen, which may put a significant and sudden strain on the healthcare system. Mapping of Poaceae pollen sources within Sydney and accurate prediction of pollen concentrations are the first steps to an advanced warning system necessary to pre-empt the healthcare resources needed during pollen season.
Background Asthma affects approximately 11% of Australia’s population and allergic rhinitis 19%. Grass pollen is associated with asthma and allergic rhinitis exacerbations. This study tested the hypothesis that days with extreme numbers of general practice (GP) encounters for asthma and allergic rhinitis aligned with grass pollen season. Methods The MedicineInsight GP database contains longitudinal data on persons attending a sample of Australian GPs. We created time series of daily counts of asthma and allergic rhinitis encounters by state and territory to identify extreme encounter days; days with counts above the 99th percentile. Results Of 3,036,678 attendances during the study period, 2.4% were for asthma. There were 83 extreme encounter days during April to December, across Australia. Victoria and South Australia had the highest increase in attendances on extreme days. Allergic rhinitis encounters represented 0.9% of attendances. Of the 69 extreme allergic rhinitis encounter days across Australia, Victoria and Australian Capital Territory had the highest increase in attendances. Allergic rhinitis extreme days were clustered between mid-October and early December (72%), compared to 22% of the asthma extreme days. Conclusions Extreme asthma GP encounters were not as strongly associated with grass pollen season compared to allergic rhinitis encounters. Victoria had a high number of encounters on asthma and allergic rhinitis extreme days, many associated with thunderstorm asthma. Key messages Extreme asthma encounter days can be associated with cooler months, grass pollen season and school holidays. Extremes allergic rhinitis presentation days were aligned with grass pollen season.
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