title: Association of the shuffling of Streptococcus pyogenes clones and the fluctuation of scarlet fever cases between 2000 and 2006 in central Taiwan.
abstract: BACKGROUND
  The number of scarlet fever occurrences reported between 2000 and 2006 fluctuated considerably in central Taiwan and throughout the nation. Isolates of Streptococcus pyogenes were collected from scarlet fever patients in central Taiwan and were characterized by emm sequencing and a standardized pulsed-field gel electrophoresis (PFGE) method. National weekly report data were collected for investigating epidemiological trends.
  
  
  RESULTS
  A total of 23 emm types were identified in 1,218 S. pyogenes isolates. The five most prevalent emm types were emm12 (50.4%), emm4 (23.2%), emm1 (16.4%), emm6 (3.8%) and emm22 (3.0%). PFGE analysis with SmaI suggested that, with a few exceptions, strains with a common emm type belonged to the same clone. There were two large emm12 clones, one with DNA resistant to cleavage by SmaI. Each prevalent emm clone had major PFGE strain(s) and many minor strains. Most of the minor strains emerged in the population and disappeared soon after. Even some major strains remained prevalent for only 2-3 years before declining. The large fluctuation of scarlet fever cases between 2000 and 2006 was associated with the shuffling of six prevalent emm clones. In 2003, the dramatic drop in scarlet fever cases in central Taiwan and throughout the whole country was associated with the occurrence of a severe acute respiratory syndrome (SARS) outbreak that occurred between late-February and mid-June in Taiwan.
  
  
  CONCLUSIONS
  The occurrences of scarlet fever in central Taiwan in 2000-2006 were primarily caused by five emm types, which accounted for 96.8% of the isolates collected. Most of the S. pyogenes strains (as defined by PFGE genotypes) emerged and lasted for only a few years. The fluctuation in the number of scarlet fever cases during the seven years can be primarily attributed to the shuffling of six prevalent emm clones and to the SARS outbreak in 2003.
authors.affiliation: The Central Region Laboratory, Center for Research and Diagnostics, Centers for Disease Control, Taichung City 40855, Taiwan. nipmcsc@cdc.gov.tw
authors.forename: Chien-Shun
authors.initials: CS
authors.lastname: Chiou
authors.forename: You-Wun
authors.initials: YW
authors.lastname: Wang
authors.forename: Pei-Ling
authors.initials: PL
authors.lastname: Chen
authors.forename: Wan-Ling
authors.initials: WL
authors.lastname: Wang
authors.forename: Ping-Fuai
authors.initials: PF
authors.lastname: Wu
authors.forename: Hsiao-Lun
authors.initials: HL
authors.lastname: Wei
mesh_terms: D015373:Bacterial Typing Techniques; D004196:Disease Outbreaks; D016521:Electrophoresis, Gel, Pulsed-Field; D005838:Genotype; D006801:Humans; D015994:Incidence; D017720:Molecular Epidemiology; D012541:Scarlet Fever / Q000453:epidemiology*; D013297:Streptococcus pyogenes / Q000235:genetics* / Q000302:isolation & purification; D013624:Taiwan / Q000453:epidemiology