Epidemiological trends of invasive Streptococcus pyogenes infections in Catalonia, 2022-2024: a two-year analysis

Invasive group A streptococcal (iGAS) infections resurged across Europe in late 2022. We aimed to describe the incidence, clinical characteristics, and outcomes of iGAS in Catalonia over two epidemic seasons (2022/23 and 2023/24), and to identify risk factors associated with mortality.

A prospective study was conducted including all confirmed iGAS cases reported to the Microbiological Reporting System of Catalonia between October 2022 and October 2024. Epidemiological and clinical data were collected from medical files and incidence rates (IRs) calculated. Multivariable logistic regression was used to assess risk factors associated with mortality.

A total of 589 laboratory-confirmed iGAS cases were included; 416 cases (70.6%) from 2022/23 season, and 173 (29.4%) from 2023/24. The overall IR decreased from 5.3 to 2.2 cases per 100,000 population (p < 0.001). In 2022/23, incidence was higher in children (0-14 years) than in adults (9.8 vs. 4.6 per 100,000; p < 0.001), whereas this pattern reversed in 2023/24 (1.7 vs. 2.3; p = 0.028). Pleural empyema predominated in children, while skin and soft tissue infections with bacteraemia in adults. Respiratory viral coinfections were more common in children than in adults (47.1% vs. 10.8%; p < 0.001). Overall, 97.3% of patients were hospitalized, and 26.9% required intensive care (33.3% in children vs. 25.2% in adults; p = 0.08). Overall mortality was 11.3% (12.9% in adults and 5.8% in children: p < 0.05). Multivariable analyses showed age, respiratory viral coinfections, chronic renal disease, and intensive care unit admission independently associated with mortality.

The decline in iGAS incidence in 2023/24 was accompanied by a shift in age distribution and a reduction in respiratory viral coinfections, suggesting a return toward pre-pandemic epidemiological patterns. Further research is needed to clarify pathogenic mechanisms and outcome determinants.