title: Invasive infections due to Streptococcus pyogenes: seasonal variation of severity and clinical characteristics, Iceland, 1975 to 2012.
abstract: 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.
authors.affiliation: Department of Medicine, Landspitali University Hospital, Reykjavik, Iceland.
authors.forename: L B
authors.initials: LB
authors.lastname: Olafsdottir
authors.forename: H
authors.initials: H
authors.lastname: Erlendsdóttir
authors.forename: J
authors.initials: J
authors.lastname: Melo-Cristino
authors.forename: D M
authors.initials: DM
authors.lastname: Weinberger
authors.forename: M
authors.initials: M
authors.lastname: Ramirez
authors.forename: K G
authors.initials: KG
authors.lastname: Kristinsson
authors.forename: M
authors.initials: M
authors.lastname: Gottfredsson
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D001426:Bacterial Proteins; D002352:Carrier Proteins; D002648:Child; D002675:Child, Preschool; D006801:Humans; D007055:Iceland / Q000453:epidemiology; D015994:Incidence; D008875:Middle Aged; D011159:Population Surveillance; D012189:Retrospective Studies; D012621:Seasons; D012720:Severity of Illness Index; D017678:Sex Distribution; D013290:Streptococcal Infections / Q000175:diagnosis* / Q000453:epidemiology / Q000382:microbiology; D013297:Streptococcus pyogenes / Q000235:genetics / Q000302:isolation & purification* / Q000472:pathogenicity*; D014774:Virulence; D055815:Young Adult
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; C099983:Emm2 protein, Streptococcus pyogenes