Icelandic pediatric nasopharyngeal carriage isolates, Feburary-March 2023, Day

In Iceland invasive Streptococcus pyogenes (aka Group A Streptococcus, GAS) infections have been continuously epidemiologically surveyed since 1975, and nasopharyngeal carriage of GAS in children attending day care centers (DCC) has been seasonally surveyed annually since 2009. An unprecedented increase in pediatric invasive Group A Streptococcal (iGAS) infections was observed in Iceland in early 2023. Pediatric iGAS infections increased 8-fold from a mean of 2.0/100.000 for 1975-2022 to 16.5/100.000 for early 2023. Contemporaneously, asymptomatic nasopharyngeal GAS carriage among healthy children increased 3.5-fold from a mean 8.0% for 2009-2020 to 28.5% in early 2023. The invasive infection and carriage isolates were of multiple GAS M-types, with M1s predominant in both cohorts. To facilitate comparison of the GAS invasive infection (see Bioproject PRJNA1076228) and nasopharyngeal carriage isolates, Illumina paired-end whole genome sequencing was done on all 113 isolates from GAS positive pediatric nasopharyngeal swabs. A comparison of the GAS invasive infection and asymptomatic carriage isolates found isolates of the same M-type to be phylogenetically intermingled, showing the invasive infection and asymptomatic carriage isolates to stem/arise from the same genetic pool, and consistent with the pool of nasopharyngeal carriage GAS in the human host population being a reservoir of transmission contributing to GAS invasive infections in the population.