Outcomes and associated risk factors among hospitalisations attributed to invasive group A streptococcal disease in Northern Queensland, Australia: a 21-year population-based data linkage study.

PURPOSE: Invasive group A Streptococcus (iGAS) disease is associated with substantial morbidity and mortality. This study aimed to assess the outcomes of iGAS infection and associated risk factors in Northern Queensland, Australia. METHODS: A retrospective cohort study was conducted using linked hospital data from 2000 to 2020. iGAS cases were identified using ICD-10-AM diagnosis codes in administrative health datasets. Mortality and disease burden were analysed, and risk factors for adverse outcomes were assessed using logistic regression and competing risks regression. Disability-Adjusted Life Years (DALYs) were estimated to quantify disease burden. RESULTS: A total of 933 iGAS related hospitalisations were identified among 870 individuals. The mean age of the cohort was 45 years (SD = 24), with a median age of 61 years (IQR: 48-77 years). Hospitalised case fatality rate was 5.2%. Intensive Care Unit (ICU) admission was required for 219 patients (23.5%). Readmissions occurred in 2.0% of cases, and 3.6% experienced recurrent infection. Most deaths were attributable to sepsis (80%), with necrotising fasciitis (18%) and septic shock (13.3%) also contributing. In multivariable analysis, age ≥ 60 years was associated with lower odds of ICU admission, while female sex, non-Indigenous status, higher Socio-Economic Indexes for Areas (SEIFA) decile, cardiac disease, and renal failure were associated with increased odds of ICU admission (p < 0.01). Older age, non-Indigenous status and renal failure were significantly associated with increased mortality (p < 0.01). The total DALY burden was 1,375 years. CONCLUSION: iGAS imposes a substantial health burden in Northern Queensland, characterised by significant morbidity and high advanced health resource utilisation. Identification of high-risk groups highlights opportunities for targeted prevention of adverse health outcomes of iGAS.