Virtual Poster Presentation Australian Society for Microbiology Annual Scientific Meeting 2022

Density and diversity of Strep A emm-types to inform sore throat and skin sore epidemiology and transmission (#212)

Janessa Pickering 1 , Mark Davies 2 , Dylan D Barth 1 , Slade Sibosado 1 , Liam Bedford 1 , Bernadette Wong 1 , Scott Winslow 1 , Tim Barnett 1 3 , Jonathan Carapetis 1 , Asha Bowen 1 4
  1. Telethon Kids Institute, University Of Western Australia, Subiaco, WA, Australia
  2. Department of Microbiology and Immunology, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia
  3. School of Biomedical Sciences, University of Western Australia, Nedlands, WA, Australia
  4. Department of Infectious Diseases, Perth Children’s Hospital, Nedlands, WA, Australia

Background:

Group A streptococcus (Strep A) is a globally important pathogen. High quality surveillance data will be required to evaluate future Strep A vaccine introduction, particularly impacts on strain-specific disease prevalence and herd immunity. An understanding of transmission in endemic settings also informs vaccine strategy. Consequently, we investigated Strep A density and diversity in a cohort of remote-living children in Western Australia (WA) who experience high rates of Strep A infection.

Methods:

We utilised samples from the Missing Piece Surveillance Study (1) (based in two school sites in the Kimberley, WA) which comprised of cross-sectional screening twice per year and weekly active surveillance over 9 months. Children were assessed for Strep A pharyngitis and impetigo. Throat and skin swabs were collected, Strep A were isolated, and whole genome sequenced to derive emm-types, resistance and virulence profiles. speB quantitative PCR was performed directly on swab specimens to determine Strep A density. Densities were compared within clinical sources and inferred to be due to single emm­-types.

Results:

Eighty-two Strep A isolates were derived from 470 swab specimens. Sixteen unique emm-types were identified, with 12, 1, 44 and 70 being most prevalent. Six of 16 emm-types were found in pharyngitis, carriage, or skin only. emm-type densities were not stable across clinical sources or within individuals over time, with wide ranges (0.02pg/µL->1000pg/µL) evident in most prevalent types. Participants displayed a myriad of infectious patterns, including long term carriage, repeat infection due the same strain, and concurrent skin and throat infections due to the same emm type.

Conclusion:

Dynamic transmission between host niches and within schools was evident. In settings where Strep A throat and skin infections are prevalent, sampling pharyngitis cases only would not provide adequate coverage to inform epidemiological burden. Density measures add complexity, yet is a secondary metric for routine surveillance. Future work will encompass the preparation of detailed transmission maps and comparative genomics.

  1. 1. BARTH DD, MULLANE MJ, SAMPSON C, CHOU C, PICKERING J, NICOL MP, DAVIES MR, CARAPETIS J, BOWEN AC. Missing Piece Study protocol: prospective surveillance to determine the epidemiology of group A streptococcal pharyngitis and impetigo in remote Western Australia. BMJ Open. 2022;12(4):e057296.