The epidemiology of invasive group A streptococcal disease in Victoria, 2007-2017: an analysis of linked datasets

Objective: To describe the incidence and severity of invasive group A streptococcal disease (iGAS) in Victoria, Australia. Methods: Retrospective analysis of iGAS cases identified in linked datasets, 2007-2017: laboratory data from the Victorian Hospital Pathogen Surveillance Scheme; hospitalisation data from the Victorian Admitted Episodes Dataset; and deaths reported by the Australian Coordinating Registry. Results: There were 1,369 confirmed and 610 probable cases of iGAS identified from 2007 to 2017 in Victoria, Australia. The median annual incidence was 3.1 (range 2.4-5.2) per 100,000 population. The incidence was highest in 2017, with 5.2 (95%CI: 4.6-5.8) cases per 100,000 population. The median length of stay in hospital was 10 days, with 33.1% (578/1,744) of cases admitted to the intensive care unit, of whom 49.5% (286/578) were mechanically ventilated. The case fatality rate was 5.6% (110/1,979), reaching 13.5% (51/378) among those aged 75 years or older. Conclusions: There was an increased incidence of iGAS in 2017 in Victoria, with substantial healthcare utilisation and a high case fatality rate among older Victorians. Implications for public health: These data support mandatory notification of iGAS, which will enable better characterisation of the disease, rapid identification of changes in epidemiology and targeted public health responses.