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Multicenter Study
. 2025 Nov;44(11):2677-2684.
doi: 10.1007/s10096-025-05229-y. Epub 2025 Aug 5.

Role of viral coinfection in post-pandemic invasive Group A streptococcal infections in adults, a nation-wide cohort study (iGASWISS)

S Musumeci  1   2 , A MacPhail  3 , M Weisser Rohacek  4 , A Erba  4 , D Goldenberger  5 , C Lang  5 , E Colin-Benoit  6 , S L Leib  7 , P Sendi  7 , C Chuard  8 , V Erard  8 , C Fournier  8 , L Cobuccio  9 , F Tagini  9   10 , C Bertelli  10 , L Senn  9 , R Sommerstein  6   11 , G Blättler  11 , C Vieira Gomes  12 , M Moraz  12 , S Emonet  12   13 , C Strahm  14 , P Kohler  14 , S N Seiffert  15 , K Herzog  16 , D Vuichard Gysin  16 , S D Brugger  17 , O Nolte  18 , A Egli  18 , D Weller  17 , A M Andrianaki  17 , A S Zinkernagel  17 , D-L Vu  19 , A Uribe Caparros  19 , G Laurie  19 , N Gaia  20 , V Lazarevic  20 , P François  20 , J Schrenzel  20   13
Affiliations
Multicenter Study

Role of viral coinfection in post-pandemic invasive Group A streptococcal infections in adults, a nation-wide cohort study (iGASWISS)

S Musumeci et al. Eur J Clin Microbiol Infect Dis. 2025 Nov.

Abstract

Objective: During the winter season of 2022-2023, numerous countries experienced a surge in invasive Streptococcus pyogenes (iGAS) infections. The role of viral coinfections in the post-COVID surge has not been elucidated. We report nation-wide data describing clinical presentation, microbiological characteristics, and associations with viral infection in adults during this period.

Methods: A multicenter retrospective cohort study was conducted across 10 hospitals in Switzerland, including adults (> 16 years old) with iGAS infection from November 2022 to February 2023. Descriptive analysis was performed. A multivariable logistic regression model was fitted to assess the impact of viral coinfection. In addition, genetic analysis was performed in available isolates.

Results: A total of 194 patients were included, with a median age of 50 years (interquartile range [IQR]: 37-69). 17/194 (8.8%) were immunosuppressed and 40/194 (20.6%) exhibited concomitant viral infections, predominantly Influenza A (21/40, 53%). Illness severity was high: 65/194 (33.5%) of cases necessitated admission to an intensive care unit (ICU), and the 30-day mortality was 4% (n = 8). Among the available strains for genetic analysis (n = 48), heterogeneity was found although ST28-emm1 isolates (also known as M1UK) was predominant (22/48).

Conclusion: The post-COVID iGAS surge in Switzerland was associated with high levels of morbidity and mortality in immunocompetent adults. M1UK was predominant within the iGAS strains circulating in Switzerland during the study period and viral coinfection was a predictor for ICU admission and mortality.

Keywords: emm1; Invasive group a Streptococcus (iGAS); M1UK clone; Post-pandemic epidemiology; Viral coinfection.

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Conflict of interest statement

Declarations. Competing interests: The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Available strains (n = 48) genotyped via a dedicated in-house developed MLVA assay. Genotyping tree using multilocus variable-number tandem repeat analysis (MLVA) of representative isolates identified in the different Swiss Cantons. The main cluster contains 40% of strains of the collection and shows isolates harboring emm1 belonging to sequence type 28, originating from 4 different Cantons. The scale indicates the level of genetic relatedness within this set of strains based on UPGMA analysis.
Fig. 2
Fig. 2
Respiratory viral coinfections in iGAS cases and associated severity outcomes (ICU admission and/or death). The pie chart illustrates the proportional distribution of detected respiratory viruses among iGAS patients with any viral coinfection. The table shows the number of patients with each virus. The left column indicates the total number of iGAS cases associated with each detected virus. The right column displays the subset of those patients who experienced a severe outcome, defined as ICU admission and/or 30-day mortality.
See this image and copyright information in PMC

References

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