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

Genomic sequencing analysis of emm66 group A streptococcus (GAS) isolates associated with an ongoing outbreak of invasive infection in England and Wales from January 2016 (#182)

Laura Bubba 1 2 , Juliana Coelho 2 , Georgia Kapatai 2 , Roger Daniel 2 , Nick Bundle 2 , Sooria Balasegaram 2 , Charlotte Anderson 2 , Maya Gobin 2 , Colin Brown 2 , Vicki Chalker 2 , Derren Ready 2
  1. European Centre for Disease Prevention and Control (ECDC), Stockholm, Sweden
  2. Public health England, London, ENGLAND, United Kingdom

An outbreak of an uncommon type, emm66 of group A streptococcus (GAS) infection, was investigated in England and Wales, defining a case as an infected person who injects drugs, homeless, reporting problematic alcohol use, or epidemiologically linked to cases. No common source of infection was identified for the ongoing outbreak.

Whole genome sequencing (WGS) was performed on 55 emm66 GAS isolates (n=50 emm66.0, n=5 emm66.1); including 34 cases, 3 contemporaneous (2016) patients not fitting the case definition and 18 sporadic historical isolates (2005-2015). The evolutionary rate was evaluated by BEAST analysis on emm66.0. Thirty-two emm66.0 outbreak cases merged into a single clade (single nucleotide polymorphisms, SNPs average difference: 6.8, range 0-16 SNPs); the remaining two (one emm66.1) had > 90 SNPs difference with other outbreak isolates. All emm66.0 2015 historical isolates (n=6) and the three 2016 contemporaneous cases fitted into the outbreak clade (SNPs average: 6.3). Outbreak cases had an average of 4,103 SNPs distance from the other historical isolates (emm66.0 and emm66.1) and 32 from the reference strain. Within the same town, cases had an average difference of 2.6 SNPs; six clusters with zero SNPs difference were identified in five towns. The evolutionary rate was 9 bases per year.

WGS proved relatedness within outbreak cases and to non-outbreak cases in 2015-17suggesting the emm66.0 strain was introduced to England and Wales in 2015. Close links within geographically clustered individuals were also confirmed. WGS can confirm links in a difficult to define population, to help target services to prevent further cases.