title: Dynamic epidemiology of group A streptococcal serotypes associated with pharyngitis.
abstract: BACKGROUND
  Despite the past 15 years of heightened awareness of the disease-causing potential of group A streptococci, the possible epidemiological influence of rapid changes in prevalent serotypes has not been fully appreciated.
  
  
  METHODS
  We analysed throat cultures collected as part of routine medical care in a semi-closed community of nearly 500 children and adults between January, 1999, and April, 2000. beta-haemolytic streptococci from all positive cultures were characterised by serological grouping, T-agglutination pattern, and serotyping for M protein or opacity factor.
  
  
  RESULTS
  We saw an increase in the number of symptomatic individuals with pharyngitis beginning in mid-1999. Between July 1 and Dec 31, 1999, 111 (29%) of 378 throat cultures yielded group A streptococci, 102 (92%) of which were serotype M1. Between Jan 1 and Mar 31, 2000, 126 (45%) of 277 throat cultures yielded group A streptococci. Unexpectedly, 106 (84%) of these throat isolates were serotype M6, and only 16 (13%) were M1. 20 (28%) of the 71 individuals with M1 infection subsequently acquired infection with M6.
  
  
  CONCLUSIONS
  This rapid and almost complete shift in predominance of group A streptococcal serotype in this community draws attention to the dynamic epidemiology of these organisms. This change has important implications for further understanding the epidemiology of group A streptococcal infections, and for the development and use of a vaccine.
authors.affiliation: Department of Pediatrics, WHO Collaborating Center for Reference and Research on Streptococci, University of Minnesota Medical School, Minneapolis, MN 55455, USA. kapla001@umn.edu
authors.forename: E L
authors.initials: EL
authors.lastname: Kaplan
authors.forename: J T
authors.initials: JT
authors.lastname: Wotton
authors.forename: D R
authors.initials: DR
authors.lastname: Johnson
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D004196:Disease Outbreaks; D006801:Humans; D007223:Infant; D008875:Middle Aged; D010612:Pharyngitis / Q000453:epidemiology / Q000382:microbiology*; D015995:Prevalence; D012621:Seasons; D012703:Serotyping; D013290:Streptococcal Infections / Q000453:epidemiology*; D013297:Streptococcus pyogenes / Q000145:classification / Q000302:isolation & purification*; D014481:United States / Q000453:epidemiology