Background <break><break>Exposure to ambient air pollution is strongly associated with increased cerebrovascular diseases. The 201920 bushfire season in Australia burnt 5.4 million hectares of land in New South Wales alone, with smoke so severe it affected cities in Argentina, 11,000 km away. We aimed to determine the effects of i) short-term air pollution triggered by bushfires and ii) high smoke days in increasing the daily number of hospital admissions with cerebrovascular diseases.<break><break>Methods <break><break>Hospitalisation data were accessed from the admitted patient dataset from seven local Government areas of Hunter New England Local Health District. The bushfire period was defined from 1 October 2019 to 10 February 2020, and a similar period from 2018-19 as the control. High bushfire smoke days were days when the average daily concentration of particulate matter was higher than the 95th percentile of the control period. Poisson regression models and fixed effect meta-analysis were used to analyse the data.<break><break>Results <break><break>In total, 275 patients with cerebrovascular admissions were identified, with 147 (53.5%) during the bushfire (2019-20) and 128 (46.5%) in the control period (2018-19). There was no significant increase in daily cerebrovascular disease (Incidence Rate Ratio, IRR: 1.04; 95% CI: 0.98-1.05; p-value: 0.73) or ischemic stroke (IRR: 1.18; 95% CI: 0.87-1.59; p-value: 0.28) admissions over the entire bushfire period. However, the high bushfire smoke days were associated with increased ischaemic stroke-related hospital admissions with a lag of 0-1 days (IRR: 1.28; 95% CI: 1.01-1.62; I2=18.9%). In addition, during the bushfire period, particulate matter, both PM10 and PM2.5 (defined as particulates that have an effective aerodynamic diameter of 10 microns, and 2.5 microns, respectively), were also associated with increased ischaemic stroke admissions with a lag of 0 to 3 days.<break><break>Conclusion <break><break>The results suggested an association between particulate matter and high smoke days with increased hospital admissions due to cerebrovascular diseases during the recent Australian bushfire season.

Exposure to air pollution is associated with increased cardio- and cerebro-vascular diseases. However, the evidence regarding the short-term effect of air pollution on cardio- and cerebro-vascular hospitalisations in areas with relatively low air pollution levels is limited. This study aims to examine the effect of short-term exposure to different air pollutants on hospital admissions due to cardio- and cerebro-vascular diseases in rural and regional Australia with low air pollution. The study was conducted in five local Government areas of Hunter New England Local Health District (HNE-LHD). Hospitalisation data from January 2018 to February 2020 (820 days) were accessed from the HNE-LHD admitted patients’ dataset. Poisson regression model was used to examine the association between the exposure (air pollutants) and outcome variables (hospitalisation due to cardio- and cerebrovascular disease). The concentrations of gaseous air pollutants, Sulphur Dioxide (SO2), Nitrogen Dioxide (NO2), Ozone (O3), Carbon Monoxide (CO), and Ammonia (NH3) were below national benchmark concentrations for every day of the study period. In single pollutant models, SO2 and NO2 significantly increased the daily number of cardio and cerebrovascular hospitalisations. The highest cumulative effect for SO2 was observed across lag 0-3 days (Incidence Rate Ratio, IRR: 1.77; 95% Confidence Interval, CI: 1.18-2.65; p-value: 0.01), and for NO2, it was across lag 0-2 days (IRR: 1.13; 95% CI: 1.02-1.25; p-value: 0.02). In contrast, higher O3 was associated with decreased cardio- and cerebro-vascular hospitalisations, with the largest effect observed at lag 0 (IRR: 0.94; 95% CI: 0.89-0.98; p-value: 0.02). In the multi-pollutant model, the effect of NO2 remained significant at lag 0 and corresponded to a 21% increase in cardio- and cerebro-vascular hospitalisation (95% CI: 1%-44%; p-value = 0.04). Thus, the study revealed that gaseous air pollutants, specifically NO2, were positively related to increased cardio- and cerebro-vascular hospitalisations, even at concentrations below the national standards.