A Striking Increase in Carriage Among Young Children in Iceland Paralleled the Unprecedented Increase of Invasive Group A Streptococcal Infection From 2022 to 2023

Background:An unprecedented increase in pediatric invasive group A streptococcal (iGAS) infections was observed in most countries, including Iceland, in early 2023. The reasons for this rise are largely unknown. The aim of the study was to describe the parallel between nasopharyngeal (NP) carriage of group A streptococcal (GAS) in Icelandic children and the incidence of invasive disease.Methods:Electronic health records were used to identify children admitted to the Children's Hospital, Iceland, with iGAS. NP samples from asymptomatic children were collected for culture in February and March 2023 in 15 day-care centers in the greater Reykjavik area. Invasive and noninvasive isolates were characterized using whole genome sequencing. The results of the NP carriage were compared with data from 2009 to 2020.Results:Twenty-one children were diagnosed with iGAS from December 2022 to April 2023. Empyema, necrotizing fasciitis and septic or toxic shock were the most common clinical presentations. All the children were hospitalized; none died, but 9 needed intensive care. Pediatric iGAS infections increased 8-fold from a mean of 2.0/100.000 for 1975 to 2022 to 16.5/100.000 in early 2023. Asymptomatic NP GAS carriage among healthy children increased 3.5-fold from 8.0% from 2009 to 2020 to 28.5% in early 2023. Close genetic relatedness was found between carriage and invasive strains.Conclusions:The significant rise of NP GAS carriage observed in early 2023 likely contributed to the simultaneous increased incidence of iGAS. With surveillance data, microbiological culture and molecular typing, genetic similarities between invasive disease isolates and NP isolates characteristics were confirmed.