Poster Presentation Lancefield International Symposium for Streptococci and Streptococcal Diseases 2025

The Emergence and Impact of M1UK on Invasive Group A Streptococcus Disease in Aotearoa New Zealand (#43)

Anna Vesty 1 2 , Xiaoyun Ren 2 , Prachi Sharma 1 , Natalie Lorenz 1 3 , Thomas Proft 1 3 , Allan Hardaker 2 , Christina Straub 2 , Julie Morgan 2 , Audrey Tiong 2 , Anneka Anderson 4 , Rachel Webb 5 , Julie Bennett 1 6 , Philip Carter 2 , Nikki Moreland 1 3
  1. University of Auckland, Auckland, NZ, New Zealand
  2. The Institute of Environmental Science and Research, Porirua, New Zealand
  3. Maurice Wilkins Centre for Biodiscovery, The University of Auckland, Auckland, New Zealand
  4. Te Kupenga Hauora Māori, The University of Auckland, Auckland, New Zealand
  5. Department of Paediatrics, The University of Auckland, Auckland, New Zealand
  6. Department of Public Health, University of Otago, Wellington, New Zealand

A toxigenic variant of the Group A Streptococcus (GAS) emm1 lineage, known as M1UK and characterised by increased production of superantigen streptococcal pyrogenic exotoxin A (SpeA), has been associated with increases in invasive infections (iGAS) globally. These increases have been especially pronounced in the post-pandemic era concurrent with relaxation of restrictions. Recent iGAS trends in Aotearoa New Zealand (NZ) mirror those observed in other settings, though the post-pandemic surge was delayed, peaking in mid-2023. This retrospective genomic analysis explored the prevalence of M1UK in NZ over the last decade (2013-2023). The Institute of Environmental Science and Research received 417 emm1 isolates over this time period as part of passive (non-notifiable) national iGAS surveillance. Allele-specific PCRs and whole genome sequencing demonstrated that the M1UK lineage has outcompeted its M1global counterpart and by 2023 accounted for 88% of all emm1 iGAS in NZ. Phylogenetic analysis showed multiple introductions of the M1UK lineage into NZ in the last 10 years and that emm1 isolates causing iGAS are genomically related to those associated with community infections over the same time-period. Intriguingly, despite the described increase in SpeA production by M1UK,  antibody responses to SpeA were not significantly increased in children with pharyngitis caused by M1UK compared to those with M1global. The increasing trends for both iGAS and the M1UK lineage highlight a need for ongoing surveillance underpinned by genomics. iGAS became notifiable in NZ in late 2024, which is expected to improve the timeliness of detecting these events.