Background:
The emm92 group A Streptococcus (GAS) strain has been increasingly causing invasive GAS (iGAS) infections in the United States (US) since 2014 and disproportionately affects people who inject drugs (PWID) and people experiencing homelessness (PEH). Understanding the temporal and geographic spread of emm92 sub-lineages contributing to the expansion could help inform prevention and control strategies.
Methods:
We identified emm92 iGAS isolates in Active Bacterial Core surveillance (ABCs), a laboratory- and population-based surveillance system for invasive bacterial infections currently implemented in 10 US states. Whole-genome sequencing (WGS) data of isolates were used to construct a phylogenetic tree, from which sub-lineages were identified by the TreeCluster software. Temporal, geographic, and demographic features of sub-lineages were analyzed.
Results:
From 2015 to 2022, 1058 emm92 iGAS cases were documented in ABCs, with annual incidence increasing from 0.16/100,000 to 0.40/100,000 persons. Six major sub-lineages (57-291 isolates/sub-lineage) comprised nearly all isolates[1019 (96.3%)]. There was a strong association between sub-lineage and surveillance site (Cramér’s V=0.58; 95% CI 0.54-0.60). Since 2015, five sub-lineages increasingly caused iGAS infections over time, but their incidences peaked in different years; the other sub-lineage exhibited a decrease (p<0.05 for all trends, Cochran-Armitage test). The proportion of isolates differed significantly across sub-lineages for both PWID (range, 22%-44%; p<0.001, Fisher’s exact test) and PEH (range, 14%-32%; p<0.001)
Conclusions:
The recent expansion of emm92 iGAS in ABCs was associated with spread of multiple sub-lineages exhibiting varied geographic distributions, temporal dynamics, and PWID/PEH involvement, suggesting that tailored control measures may be needed for different populations.