title: Age influences the emm type distribution of pediatric group A streptococcal pharyngeal isolates.
abstract: BACKGROUND
  emm types 12, 1, 28, 3, 4, 2 and 6 (in that order) are the types most commonly associated with uncomplicated group A streptococcal (GAS) pharyngitis in the United States, together accounting for approximately 78% of isolates.
  
  
  OBJECTIVE
  To determine whether the distribution of common pharyngeal group A streptococcal GAS types differs at various ages throughout childhood.
  
  
  METHODS
  We emm typed 3356 GAS isolates collected from the United States and Canada during 3 streptococcal seasons (2000-2003). Variations in prevalence by age for the 7 most prevalent emm types and the "uncommon" category (all types accounting for <5% of the total number of isolates) were analyzed and assessed for significance by chi2.
  
  
  RESULTS
  The proportion of uncommon isolates increased significantly with increasing age from 18% in group 1 to 37% in group 4 (P = 0.001). We found a significant decrease in the proportion of the common pharyngeal emm types, specifically emm 12 and emm 4 type isolates, with increasing age (P = 0.001 and P = 0.003, respectively); there was no significant decline in the prevalence of other common pharyngeal types (emm 1, 2, 3, 6 and 28) with increasing age.
  
  
  CONCLUSIONS
  Age-related changes in emm type distribution of pharyngeal GAS are present in childhood; these changes may reflect acquisition of immunity to more common types as a consequence of exposure early in life, but this remains to be demonstrated.
authors.affiliation: Children's Memorial Hospital, Chicago, IL 60614, USA. jaggi@childrensmemorial.org
authors.forename: Preeti
authors.initials: P
authors.lastname: Jaggi
authors.forename: Robert R
authors.initials: RR
authors.lastname: Tanz
authors.forename: Bernard
authors.initials: B
authors.lastname: Beall
authors.forename: Stanford T
authors.initials: ST
authors.lastname: Shulman
mesh_terms: D000293:Adolescent; D017677:Age Distribution; D000375:Aging / Q000276:immunology*; D000942:Antigens, Bacterial / Q000145:classification* / Q000235:genetics / Q000378:metabolism; D001425:Bacterial Outer Membrane Proteins / Q000145:classification* / Q000235:genetics / Q000378:metabolism; D002352:Carrier Proteins / Q000145:classification* / Q000235:genetics / Q000378:metabolism; D002648:Child; D002675:Child, Preschool; D006801:Humans; D010612:Pharyngitis / Q000453:epidemiology* / Q000382:microbiology*; D010614:Pharynx / Q000382:microbiology*; D011159:Population Surveillance; D015995:Prevalence; D013290:Streptococcal Infections / Q000453:epidemiology / Q000382:microbiology; D013297:Streptococcus pyogenes / Q000145:classification* / Q000302:isolation & purification
chemical_list: D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D002352:Carrier Proteins; C014689:streptococcal M protein