Oral Presentation Lancefield International Symposium for Streptococci and Streptococcal Diseases 2025

The clinical and genomic epidemiology of invasive Streptococcus dysgalactiae subsp. equisimilis and Streptococcus pyogenes in Australia (117293)

Ouli Xie 1 , Leo Featherstone 2 , Thi Nhu An Nguyen 2 , Andrew J Hayes 2 , Miranda Pitt 3 , Stephanie Spring 4 , Alice Liu 1 , Gerry Tonkin-Hill 2 , Ravindra Dotel 5 , Neela Joshi Rai 6 , Alexander Rofe 7 , Sebastian Duchene 8 , Deborah C Holt 9 , Louise M Judd 2 , Lachlan JM Coin 2 , Vicki L Krause 10 , Matthew VN O'Sullivan 6 , Robert W Baird 11 , Katherine Bond 1 , Benjamin P Howden 2 , Tony M Korman 4 , Bart J Currie 9 , Mark R Davies 2 , Steven YC Tong 1
  1. Department of Infectious Diseases, The Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia
  2. Department of Microbiology and Immunology, The Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia
  3. Australian Institute for Microbiology and Infection, University of Technology Sydney, Sydney, NSW, Australia
  4. Monash Infectious Diseases, Monash Health, Melbourne, VIC, Australia
  5. Department of Infectious Diseases, Blacktown Hospital, Sydney, NSW, Australia
  6. Department of Infectious Diseases, Westmead Hospital, Sydney, NSW, Australia
  7. Victorian Infectious Diseases Service, The Royal Melbourne Hospital, at the Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia
  8. Department of Computational Biology, Institut Pasteur, Paris, France
  9. Global and Tropical Health Division, Menzies School of Health Research, Darwin, NT, Australia
  10. Northern Territory Centre for Disease Control, Northern Territory Department of Health, Darwin, NT, Australia
  11. Territory Pathology, Northern Territory Department of Health, Darwin, NT, Australia

Background

Streptococcus dysgalactiae subsp. equisimilis (SDSE) is closely related to Streptococcus pyogenes (StrepA). We compared the clinical and genomic epidemiology of invasive SDSE (iSDSE) to invasive StrepA across different settings in Australia.

Methods

Cases of iSDSE (n=693) were retrospectively identified (January 2011-February 2023) across five hospital networks in urbanised south-east (SE) Australia and the tropical Top End of the Northern Territory and compared to co-collected invasive StrepA cases (n=995). Genomic transmission clusters were inferred using single nucleotide variant thresholds from transmission studies (SDSE ≤7, StrepA ≤5). Penicillin binding protein sequences were examined for mutations associated with increased penicillin MIC.

Findings

In SE Australia, iSDSE incidence was comparable to invasive StrepA but unlike StrepA, did not dramatically decline in 2020-2021 during COVID-19 non-pharmaceutical interventions. In the Top End where StrepA is hyperendemic, iSDSE incidence was four-fold lower than StrepA but remained greater than SE Australia and disproportionately affected First Nations Australians.

In lineages with ≥5 cases, only 6% (24/384) of iSDSE cases were assigned genomic transmission clusters compared to 52% (271/524) for StrepA. A stG62647-lineage encompassed 26% (113/436) of sequenced iSDSE isolates with rapid expansion inferred between 1990-2005 in Australia. Analysis of SDSE PBP2x found 3 isolates with mutations in, and 31 isolates with mutations within 10 amino acids, of an active site motif.

Conclusion

There is a substantial burden of iSDSE dominated by the emergent stG62647-lineage. The contrasting epidemiology in different disease settings and genomic infection patterns indicate cross-pathogen transmission and host-pathogen differences with implications for disease control measures.