Invasive Group A Streptococcal Disease in Persons Experiencing Postpandemic Homelessness in Canada

Both invasive group A streptococcal (iGAS) infections and the number of persons experiencing homelessness (PEH) are increasing. Protection of PEH from the burden of iGAS infections requires understanding of its epidemiology.

To assess whether the resurgence of iGAS infections after the COVID-19 pandemic included PEH.

This cross-sectional study of population-based iGAS surveillance used Canada's National Microbiology Laboratory for emm typing and Statistics Canada and point-in-time counts to identify denominators. Participants included 503 persons with iGAS infections from January 1, 2022, to December 31, 2023, in the Toronto and Peel Region, Canada (population, 4.5 million).

The main outcome was disease incidence among PEH over time and compared with housed persons. Secondary outcomes were differences in risk factors, presentation, disease severity, and infecting emm types between PEH and housed persons.

Ninety iGAS cases occurred among PEH (median age, 47.0 years [IQR, 37.7-59.5 years]; 66 men [73.3%]) and 413 occurred among housed adults (median age, 58.9 years [IQR, 42.1-73.3 years]; 259 men [62.7%]). iGAS incidence among PEH increased from 270.4 (95% CI, 184.5-383.2) per 100 000 per year in 2022 to 451.2 (95% CI, 348.2-575.7) per 100 000 per year in 2023 (incidence rate ratio [IRR], 1.67; 95% CI, 1.06-2.69), not significantly different than the increase from 3.4 to 7.0 per 100 000 per year among housed persons (IRR, 2.05; 95% CI, 1.67-2.52). iGAS incidence overall was 70.7-fold higher (95% CI, 56.3-fold to 88.7-fold) among PEH than housed persons. Compared with housed adults, PEH were less likely to be immunocompromised (adjusted odds ratio [AOR], 0.29; 95% CI, 0.11-0.73) and were more likely to be persons who inject drugs (AOR, 5.06; 95% CI, 2.79-9.19), to have nonintact skin (AOR, 4.16; 95% CI, 2.45-7.04), and to have iGAS presenting as soft tissue infection (AOR, 1.64; 95% CI, 1.02-2.64). PEH were less likely to die of iGAS than housed adults (AOR, 0.33; 95% CI, 0.12-0.95). Overall, emm1 and emm12 caused 33.7% of iGAS cases (137 of 406) among housed persons, but only 2.2% (2 of 90) among PEH; in contrast, isolates with emm types 49, 74, 80, 82, and 92 caused 77.8% of iGAS cases (70 of 90) among PEH, but only 34.2% (139 of 406) among housed persons (P < .001). The emm types frequently causing iGAS infections among PEH also caused iGAS infections among housed persons and were too highly clonal to assess transmission risk.

In this cross-sectional study, the post-COVID-19 pandemic resurgence of iGAS infections occurred among both PEH and housed adults, although the incidence among PEH was 70.7-fold greater. Risk factors, clinical presentations, outcomes, and infecting strains were very different. Improved iGAS protection for PEH, such as vaccines, is needed.