To determine age-specific and age-standardised incidence trends of acute rheumatic fever (ARF) or rheumatic heart disease (RHD) among Indigenous Western Australians aged less than 35 years of age.

A population-based retrospective cohort study with linked data analysis.

Western Australian hospital admissions (1996–2022) and RHD notifications to the state-based register (2011–2015).

Patients, both Indigenous and non-Indigenous aged

Of 1746 incident ARF/RHD cases, 1526 (87%) were Indigenous peoples, with the highest rates observed in patients aged 5–14 years, with an annual estimated increase of 4.3% (95% CI 3.2% to 5.2%). The 0–4 years age group experienced an annual increase in incidence rates of 4.8% (95% CI 1.4% to 8.2%). Overall, Indigenous patients experienced an annual increase of 1.9% (95% CI 1.3% to 2.6%) from 1996 to 2022. However, most cases (n=894) were identified after multiple significant policy developments (2011–2022) with an annual increase of 5.7% (95% CI 3.7% to 7.5%) for this period.

Increasing trends of incident ARF/RHD were observed in Indigenous patients aged under 15 years, with the greatest annual increments observed after policy implementation for disease reporting and awareness in the period from 2011 to 2022. Improvement in case ascertainment of ARF/RHD may be contributing towards increasing trends with improved reporting and monitoring of incident cases in very young Indigenous Australians more recently.