Bushfire-smoke trigger hospital admissions with cerebrovascular diseases: evidence from 2019-20 bushfire in Australia

Background Exposure to ambient air pollution is strongly associated with increased cerebrovascular diseases. The 2019–20 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. Methods 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 95 th percentile of the control period. Poisson regression models and fixed effect meta-analysis were used to analyse the data. Results 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; I 2 =18.9%). In addition, during the bushfire period, particulate matter, both PM 10 and PM 2.5 (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. Conclusion 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.