Oral Presentation 20th Lancefield International Symposium on Streptococci and Streptococcal Diseases 2017

The utility of Whole Genome Sequencing in Group A Streptococcus outbreaks in England – a perspective from the reference laboratory (#36)

Juliana Coelho 1 , Georgia Kapatai , Roger Daniel , Derren Ready , Vicki Chalker
  1. Publich Health England, London, LONDON, United Kingdom

Streptococcus pyogenes infection may have serious outcomes for patients and clusters and require management and control of onward transmission. RVPBRU routinely performs emm typing of isolates from invasive disease and also superficial isolates linked to clusters. Whole Genome Sequencing (WGS) is increasingly being requested by public health professionals during outbreak investigations. RPVBRU investigated 91 GAS/iGAS transmission events queries between 2016/2017, where two or more isolates were received for typing. Surveillance data for iGAS indicates that the five most common emm types in England are emm 1.0, 89.0, 12.0, 28.0 and 94.0. Interestingly, they were responsible for 36 of the 91 clusters (39.6%; 10, 9, 6, 6 and 5 clusters, respectively).

Four prolonged outbreaks with iGAS/GAS strains (two emm 1.0; one emm 5.23; one emm 11.0) were investigated. The emm 1.0 strains from two care homes and one shared staff member displayed 0-2 SNPs difference (average SNP variation between sporadic, contemporaneous emm 1.0 isolates was 29.8), suggesting a transmission event. Analysis of another emm 1.0 cluster in a maternity unit revealed that the isolates were not related (20 and 24 SNPs difference).

Phylogenetic analyses of the emm 5.23 and emm 11.0 clusters revealed that all cluster-related isolates co-located within the same clade distinct from contemporaneous sporadic isolates of the same emm type, suggesting that persistence rather than strain reintroduction was responsible for these two cases. These results demonstrate that the implementation of WGS analysis is a viable alternative and provides finer resolution to outbreak investigations.