12 Oct 2022
Unlocking epidemiology of invasive group A Streptococcus disease (iGAS) in Victoria
A team of researchers from the Doherty Institute undertook a statewide analysis to characterise the incidence and severity of invasive group A Streptococcus disease (iGAS) in Victoria, Australia using linked administrative datasets.
Group A Streptococcus (GAS) is a type of bacteria commonly found in the throat and on the skin. While GAS can primarily cause non-invasive infections such as pharyngitis, in rare cases, the bacteria can also lead to severe, life-threatening infections known as iGAS, including necrotising fasciitis, osteomyelitis, and streptococcal toxic shock syndrome.
In this study published in the Australian and New Zealand Journal of Public Health, researchers compiled, linked and analysed a large amount of data from multiple sources across the state to investigate the incidence and severity of iGAS. The result is the most comprehensive picture of the true burden and epidemiology of iGAS in Victoria between 2007 and 2017.
Between 1 January 2007 and 31 December 2017, 1,979 cases of iGAS were identified in the state, with a median annual incidence of 3.1 cases per 100,000 population.
Of the 88 per cent of cases with hospitalisation information, the median length of stay in hospital was 10 days, of whom 33 per cent were admitted to the intensive care unit. The case fatality rate was 5.6 per cent over the decade.
Researchers observed a considerably higher number of iGAS cases in 2017 compared to previous years (158 cases in 2007 to 327 cases in 2017), and that this increase occurred suddenly rather than as a gradual increase over time, resulting in the highest incidence recorded that year (5.2 cases per 100,000 population).
The team also found that 12 of the 20 cases where there was a co-infection with influenza occurred in 2017, when Victoria had a large influenza outbreak. This led the researchers to recommend further investigation into the potential for influenza epidemics to drive a surge in iGAS cases.
Royal Melbourne Hospital’s Dr Katherine Gibney, infectious diseases physician, public health physician and medical epidemiologist at the Doherty Institute, said that linking the multiple datasets is a is a particular strength of this study.
“For the first time, we’ve been able to analyse additional demographic and clinical factors, compared to prior Victorian research, and this enabled us to better understand iGAS incidence and severity than previous studies,” Dr Gibney said.
“This linked dataset approach has the potential to unlock our ability to identify and respond to epidemiological trends and outbreaks, especially now that iGAS has been made notifiable in Victoria.
“Our results support the recent introduction of mandatory disease notification at a national level. Ongoing surveillance data arising from mandatory notification will help to identify key populations at greater risk of iGAS and enable health departments and clinicians to provide prophylaxis to close contacts to prevent additional iGAS cases.
“Eventually, this could be used to target interventions, such as prophylactic antibiotics or future vaccines, to the highest risk groups,” Dr Gibney concluded.
Examining linked datasets, this study covers all age groups and geographic locations in Victoria, with maximum case and outcome ascertainment to better describe iGAS incidence and severity than previous studies.
Funding: National Health and Medical Research Council (NHMRC) and RACP Foundation