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

TL;DR

In Canada, homeless people had a 70-fold higher rate of severe strep infections than housed people after the pandemic, with different risk factors and bacteria strains involved.

Contribution

Shows that homeless populations face a disproportionately higher burden of iGAS infections with distinct epidemiological patterns post-pandemic.

Findings

iGAS incidence was 70.7-fold higher among persons experiencing homelessness compared to housed individuals.

Persons experiencing homelessness were more likely to have nonintact skin and inject drugs, and less likely to be immunocompromised.

Different emm types caused iGAS in homeless versus housed populations, with emm49, 74, 80, 82, and 92 prevalent in homeless individuals.

Abstract

During the post–COVID-19 pandemic resurgence, how did invasive group A streptococcal (iGAS) infection compare between persons experiencing homeless (PEH) and housed persons?

This cross-sectional study demonstrated that iGAS increased among both PEH and housed persons; PEH were less likely to be immunocompromised, but more likely to be persons who inject drugs, to have nonintact skin, and to present with soft tissue infection. iGAS was 70.7-fold more common among PEH than housed persons and emm types causing disease were different between the groups.

The post–COVID-19 pandemic iGAS resurgence included PEH despite very different iGAS epidemiology between PEH and housed persons.

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.

This cross-sectional study compares the resurgence of invasive group A streptococcal (iGAS) infections after the COVID-19 pandemic between persons experiencing homelessness and housed persons.

Figures