Increase in Invasive Group A Streptococcal Disease and Emergence of Mucoid Strains in a Pediatric Population: February-June 2017

Infection with group A Streptococcus (GAS) can cause severe systemic and locally invasive disease. Invasive group A streptococcal (iGAS) disease incidence varies both seasonally and year-to-year, and it may exhibit clustered outbreaks. We observed an upswing in iGAS cases at a tertiary care Children's Hospital, prompting further characterization of local iGAS disease. Methods: Cases of iGAS disease were abstracted from the medical record by manual chart review of all positive screening tests and cultures for GAS over a 4-year span. Incidence rates per 1000 hospital admissions and per 100 positive GAS tests were calculated and compared. Selected isolates were further characterized by whole-genome sequencing. Results: Significant year-to-year differences in per-admission iGAS incidence rate were observed in February and June, although per-positive test incidence rates were not significantly different. Whole-genome sequencing revealed 2 dominant serotypes - emm3 and emm6 - with high rates of mucoid phenotype and systemic bacteremia. Conclusions: We document a significant but transient increase in iGAS disease incidence in 2 months of 2017. Genome sequencing revealed 2 dominant serotypes associated with mucoid phenotypes and severe disease, highlighting the dynamic nature of iGAS disease pattern.