Invasive infections due to Streptococcus pyogenes: seasonal variation of severity and clinical characteristics, Iceland, 1975 to 2012

Euro Surveill. 2014 May 1;19(17):5-14.


Epidemiology and clinical characteristics of invasive Group A streptococcal infections (IGASI) are highly variable. Long-term studies are needed to understand the interplay between epidemiology and virulence. In a population-based study of IGASI in Iceland from 1975 to 2012, 288 cases were identified by positive cultures from normally sterile body sites. Charts were reviewed retrospectively and emm-types of viable Streptococcus pyogenes isolates (n=226) determined. Comparing the first and last decade of the study period, IGASI incidence increased from 1.09 to 3.96 cases per 100,000 inhabitants per year. The most common were emm types 1 (25%), 28 (11%) and 89 (11%); emm1 strains were most likely to cause severe infections. Infections in adults were significantly more likely to be severe during the seasonal peak from January to April (risk ratio: 2.36, 95% confidence interval: 1.34–4.15). Significant seasonal variability in severity was noted among patients with diagnosis of sepsis, respiratory infection and cellulitis, with 38% of severe infections in January to April compared with 16% in other months (p<0.01). A seasonal increase in severity of IGASI suggested that generalised seasonal increase in host susceptibility, rather than introduction of more virulent strains may play a role in the pathogenesis of these potentially fatal infections.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Age Distribution
  • Aged
  • Aged, 80 and over
  • Bacterial Proteins
  • Carrier Proteins
  • Child
  • Child, Preschool
  • Humans
  • Iceland / epidemiology
  • Incidence
  • Middle Aged
  • Population Surveillance
  • Retrospective Studies
  • Seasons
  • Severity of Illness Index
  • Sex Distribution
  • Streptococcal Infections / diagnosis*
  • Streptococcal Infections / epidemiology
  • Streptococcal Infections / microbiology
  • Streptococcus pyogenes / genetics
  • Streptococcus pyogenes / isolation & purification*
  • Streptococcus pyogenes / pathogenicity*
  • Virulence
  • Young Adult


  • Bacterial Proteins
  • Carrier Proteins
  • Emm2 protein, Streptococcus pyogenes