Introduction. Since September 2022, an increase in iGAS infections has been reported with different time waves around the world.
Materials and Methods. In the years 2023-2024, 777 reports of iGAS were received, of which 372 were accompanied by the bacterial strain. Demographic and clinical characteristics were collected using a standardized form. iGAS strains were characterized by emm sequence typing, speA and speC genes, susceptibility testing to erythromycin and clindamycin. emm1 isolates were distinguished between M1global and M1UK variants.
Results. The most vulnerable age groups were 0-9 years (22%) and 70-79 years (19%). Unlike the usual seasonal trend with spring and winter peaks, in 2023 the period of greatest iGAS diffusion extended from spring until midsummer. emm1 (about 45%) was the dominant serotype, with the emm1.0 and emm1.137 subtypes being the most frequent, followed by emm 12 (10%). The emerging emm3.93 serotype has only been detected since 2024.
All the emm1 isolates possessed the superantigen speA gene and approximately 50% belonged to the M1UK variant. Resistance rates to erythromycin and clindamycin were about 6%.
Conclusions
The spread of iGAS infections was devoid of the classical seasonality in Italy in 2023. This anomalous trend was probably responsible for the large number of reported iGAS infections, which doubled those of the following year. Although geographic differences in emm type-subtype distribution were noted, emm1 was primarily responsible for iGAS while the emerging emm3.93 type was poorly represented. Macrolide-resistant iGAS, reported as a medium priority by the WHO, do not constitute an alert in Italy.