Invasive GAS Resurgence in Persons Experiencing Homelessness

In a population-based surveillance analysis from Toronto and Peel Region, invasive group A Streptococcus infections resurged after the COVID-19 pandemic among adults, with sharply different reported burden between persons experiencing homelessness and housed adults in a two-year dataset drawn from invasive group A Streptococcus (iGAS) surveillance. The authors describe surveillance spanning January 1, 2022, through December 31, 2023, in which 558 total iGAS cases (55 in children and 503 in adults) were identified, including 90 cases among adults experiencing homelessness. The analysis centers on comparing incidence patterns along with clinical features and strain distributions across the two housing groups.

Surveillance ascertainment was described as laboratory based across hospitals and laboratories serving the surveillance area, with case capture triggered by isolation of group A Streptococcus from sterile sites and supplemented by audits for completeness. Using denominators derived from regional population estimates and point-in-time homelessness counts, investigators report that iGAS incidence among persons experiencing homelessness increased from 270.4 (95% CI, 184.5-383.2) per 100000 per year in 2022 to 451.2 (95% CI, 348.2-575.7) per 100000 per year in 2023 (IRR, 1.67; 95% CI, 1.06-2.69). They also report overall incidence was 70.7-fold higher among persons experiencing homelessness than among housed adults (95% CI, 56.3-88.7), establishing the incidence contrast used for subsequent comparisons.

Against that incidence backdrop, the authors report differences in presenting features and risk profiles in the group experiencing homelessness. In adjusted comparisons, persons experiencing homelessness were more likely than housed adults to have nonintact skin at presentation and a primary clinical diagnosis categorized as soft tissue infection, and they were more likely to be persons who inject drugs. The age distribution also differed, with a younger median age reported among persons experiencing homelessness. Investigators also report that persons experiencing homelessness were less likely to be immunocompromised, indicating that the contrasts extended beyond exposure context to baseline host factors and clinical phenotype.

Microbiologic results likewise diverged, with the authors highlighting differences in emm-type distribution between housing groups. They report that isolates from persons experiencing homelessness were dominated by emm types 49, 74, 80, 82, and 92, while housed adults had a larger contribution from emm1 and emm12 over the same period. For the emm types enriched among persons experiencing homelessness and prioritized for genomic assessment, phylogenetic analysis was reported to show very high clonality, and the authors state that this limited what could be inferred about transmission using core single nucleotide variant comparisons. They describe this as a constraint on interpreting relatedness when dominant strains are closely related across cases.

In the discussion and conclusions, the authors frame the findings as documenting a postpandemic resurgence that included both housed adults and persons experiencing homelessness, while underscoring that epidemiology and clinical profile differed between the groups. They report that, compared with housed adults, persons experiencing homelessness differed in risk factors, clinical presentation and severity, and the infecting strains (emm types) observed. The paper’s central message, as reported, is that the resurgence coincided with markedly higher incidence among persons experiencing homelessness alongside distinct clinical characteristics and a different distribution of circulating emm types.

Key findings:

• The authors report that iGAS incidence increased over the two years studied and that persons experiencing homelessness experienced a markedly higher overall burden than housed adults.
• Compared with housed adults, investigators observed that persons experiencing homelessness more often had nonintact skin and soft-tissue presentations and injection drug use, were younger, and were less likely to be immunocompromised.
• The authors report that emm types differed by housing status and that dominant emm types among persons experiencing homelessness were highly clonal, which they state constrained transmission inference using core SNV comparisons.