Oral Presentation BACPATH 2019

Rapid transmission and replacement of diverse Streptococcus pyogenes isolates along household and community networks in rural Indigenous communities (#15)

Jake A Lacey 1 2 , Adrian Marcato 1 2 , Nicholas Geard 1 2 , David J Price 1 2 , Patricia T Campbell 1 2 3 , Rebecca H Chisholm 2 , Malcom I McDonald 4 , Deborah C Holt 4 , Phillip M Giffard 4 , Jodie McVernon 1 2 , Mark R Davies 1 2 , Steven YC Tong 1 2 4 5
  1. The Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia
  2. The University of Melbourne, Melbourne, VIC, Australia
  3. Murdoch Children’s Research Institute, Parkville, Melbourne, VIC, Australia
  4. Menzies School of Health Research, Charles Darwin University, Darwin, Northern Territory, Australia
  5. Victorian Infectious Diseases Service, The Royal Melbourne Hospital, Melbourne, VIC, Australia

Superficial infections with Streptococcus pyogenes (S. pyogenes), such as pyoderma and pharyngitis, can lead to invasive diseases, chronic renal/cardiac diseases, and early mortality. Prevalence of S. pyogenes infections in many remote Indigenous communities in the Northern Territory (NT) can be as high as 30-40% at any one time. Efforts to control superficial GAS infections and their sequelae in Indigenous populations have been hampered by an incomplete understanding of transmission dynamics and population biology.

We utilised data collected during a longitudinal household study conducted in two geographically-separated remote communities of the NT from 2003-2005. Household were selected based on a known history of rheumatic heart disease. Houses were visited on a monthly basis to screen individuals for sore throat and pyoderma. S. pyogenes isolated from skin and throat were subject to whole genome sequencing which was used to determine strain relatedness and define migration of strains throughout households and the communities.

A total of thirty-four genotypes were defined with each genotype forming distinct, closely related subgroups when compared to global isolates of the same emm/MLST type. Each genotype was only isolated for a limited amount of time within a community (<6 months). The migration of strains within and between households was investigated using pairwise comparisons. Potential transmissions between individuals was established by isolation of the same genotype at the same period in time or subsequent month with a pairwise SNP distance of <4 SNPs. Using these thresholds >100 within and between household transmission events were predicted. 

These data demonstrate the S. pyogenes population in rural indigenous communities in the NT is highly diverse but comprises of distinct sub-lineages in comparison to global isolates. Migration of stains in these communities is rapid and genotype replacement occurs frequently. These factors need to be accounted for when implementing control strategies and informing policy design, such as vaccination, to reduce the burden of S. pyogenes mediated disease in rural settings.

  1. McDonald M.I, Towers R.J , Fagan P, Carapetis J.R, and Currie B.J, (2007). Molecular typing of Streptococcus pyogenes from remote Aboriginal communities where rheumatic fever is common and pyoderma is the predominant streptococcal infection. Epidemiology and Infection, 135, pp 1398-1405.
  2. McDonald M.I, Towers R.J , Andrews R.M, Norma B, Currie B.J and Carapetis J.R (2006). Low rates of Streptococcal pharyngitis and high rates of pyoderma in Australian Aboriginal communities Where acute rheumatic fever is hyperendemic. Clinical Infectious Diseases, 43 pp683-689