Poster Presentation Lancefield International Symposium for Streptococci and Streptococcal Diseases 2025

Inference of Streptococcus pyogenes transmission pathway parameters from analyses of whole genome sequence data of isolates collected in a high burden setting (#45)

Aarón Alonso Garcia 1 , Rebecca H Chisholm 1
  1. La Trobe University, Bundoora, VIC, Australia

Background

There are critical gaps in our understanding of Streptococcus pyogenes (Strep A) transmission pathways in high-burden settings, frustrating the design of interventions to reduce transmission and disease burden.  In particular, the relative roles of the different superficial Strep A infection types (pharyngitis, skin infections, throat carriage and skin colonisation) in sustaining transmission in these settings is unknown.

Methods

A recent genomic epidemiology method has been developed that is able to identify transmission links between infection isolates based on the similarity of Whole Genome Sequence data and time of isolation [1,2]. We extend this method to infer directionality of transmission links between isolates and apply it to isolates collected from a historical longitudinal household surveillance study in a remote Australian Aboriginal community [3]. We then calibrate a novel dynamic individual-based model of Strep A transmission to this transmission link data using an efficient Bayesian inference method [4] to quantify the relative infectiousness of throat carriage and skin infections in this setting.

Results

Our results indicate that Strep A throat carriage plays a significant role in the transmission of Strep A in this high burden setting, including in the persistence of skin infections.

Conclusion

Our findings suggest that treatment programs targeting both skin infections and throat carriage are likely necessary to reduce the burden of Strep A.

  1. JA Lacey, et al. Evaluating the role of asymptomatic throat carriage of Streptococcus pyogenes in impetigo transmission in remote Aboriginal communities in Northern Territory, Australia: a retrospective genomic analysis. The Lancet Microbe 4: 524-533 (2023).
  2. O Xie, et al. Temporal and Geographic Strain Dynamics of Invasive Streptococcus Pyogenes In Australia: A Multi-Centre Clinical and Genomic Epidemiology Study 2011-2023. Preprints with the Lancet: https://ssrn.com/abstract=4799123 (2024).
  3. MI McDonald, et al., Low rates of Streptococcal pharyngitis and high rates of pyoderma in Australian Aboriginal communities where acute rheumatic fever is hyperendemic. Clin Infect Dis 43:683–689 (2006).
  4. MU Gutman and J Corander, Bayesian Optimization for Likelihood-Free Inference of Simulator-Based Statistical Models, JMLR 17: 1-47 (2016).