F2F Poster 21st Lancefield International Symposium for Streptococci and Streptococcal Diseases 2022

Modelling the effect of direct competition on the population-level strain diversity of Group A Streptococcus    (#310)

Nefel Tellioglu 1 , Jake Lacey 2 , Mark R Davies 3 , Nic Geard 1 4 , Rebecca H Chisholm 5 6
  1. School of Computing and Information Systems, University of Melbourne, Melbourne, VIC, Australia
  2. Doherty Department, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia
  3. Department of Microbiology and Immunology, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia
  4. Department of Infectious Diseases, University of Melbourne, Melbourne, VIC, Australia
  5. Department of Mathematics and Statistics, La Trobe University, Bundoora, VIC, Australia
  6. Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, VIC, Australia

Background

Group A Streptococcus (GAS) causes millions of infections annually. Interventions can be complicated by the high strain diversity often observed in disease-endemic settings. It is not well understood how high strain diversity is maintained in these populations given that strains compete with each other both directly (within an individual host) and indirectly (via host immunity). Several previous studies have investigated how indirect competition affects the prevalence and diversity of strains. However, these studies tend to make simplifying assumptions about the role of direct competition, such as virulence and metabolic type, that may occur within hosts. There is little data available to determine the validity of these assumptions and there is a need to clarify how sensitive model outputs are to these assumptions.

Methods

In this study, we develop an agent-based model which enables us to compare the epidemiological dynamics of a multi-strain pathogen under different assumptions about direct competition between strains.

Results

Our results suggest that while direct and indirect competition can each decrease strain diversity when they act in isolation, they may increase strain diversity when they act together. This indicates that GAS modelling studies should examine sensitivity to assumptions about direct competition. Ongoing model calibration using longitudinal endemic GAS surveillance data is being used to assess the effect of direct competition on population-level GAS strain diversity.

Conclusions

Omitting considerations of direct competition can lead to inaccurate estimates of the likely effectiveness of control strategies as changes in strain diversity shift the level of direct strain competition.