Contemporary trends in anaphylaxis burden and healthcare utilisation in Western Australia: A linked data study

Background: Anaphylaxis is a growing public health problem in Australia. To determine the extent of the problem, we linked multiple health datasets to examine temporal trends in anaphylaxis events across the health system in Western Australia (WA).Methods: We identified an anaphylaxis cohort from 1980 to 2020 using linked datasets from ambulance, emergency departments, hospital inpatients and deaths. Age-standardised anaphy-laxis event rates were calculated from 2010 to 2020. Dataset-specific rates for anaphylaxis were also examined, to show differences in health care utilisation. Annual percent change in rates (2010-2019) were estimated using age-adjusted Poisson regression models.Results: A total of 19 140 individuals (mean age 31 years; 51% female) experienced 24 239 anaphylaxis events between 2010 and 2020. From 2010 to 2019, the average annual percent increase (95% CI) in rates was 5.3% (4.8-5.8%), from 70.3 to 113.9, with rates reducing to 76.5/100 000 population in 2020. Adolescents and young adults aged 5-14 years and 15-24 years had the greatest increase of 6.9% (5.6-8.1%) and 6.8% (5.6-8.0) respectively, with those over 25 years increasing by approximately 5% per year and children 1-4 years showing the lowest annual in-crease of 2.6% (1.1-4.2%). The highest absolute rates were seen in under 1 year (269.7/100 000; 2019). There has been an acceleration of trends from 2015 to 2019, underpinned by large in-creases in 15-24 and 25-34 years. All databases, show similar increasing trends, with ambulance attendance (33.7 per 100 000), emergency presentation (89.8 per 100 000) and hospital admis-sions (46.2 per 100 000), for anaphylaxis highest in 2019. However, whilst ambulance and emergency presentations have grown by 8.9% (95%CI 7.9-9.8%) and 6.6% per year (95%CI 6.0- 7.2%), respectively, hospitalisations appear to be steadying with only a 0.9% (95%CI 0.2-1.6%) yearly rise.Conclusion: Rates of anaphylaxis continue to increase, with WA having higher rates than pre-vious estimates for Australia. Whilst rates are still high in infants, lower trends in children compared to older ages may indicate better prevention of allergy. Results show more people experiencing anaphylaxis now receive care in emergency and ambulance, rather than hospital. Further exploration of the patient care journey through prehospital and inpatient care is required, to understand the changing health demands of people who experience anaphylaxis.