Association of the shuffling of Streptococcus pyogenes clones and the fluctuation of scarlet fever cases between 2000 and 2006 in central Taiwan

<p>Abstract</p> <p>Background</p> <p>The number of scarlet fever occurrences reported between 2000 and 2006 fluctuated considerably in central Taiwan and throughout the nation. Isolates of <it>Streptococcus pyogenes </it>were collected from scarlet fever patients in central Taiwan and were characterized by <it>emm </it>sequencing and a standardized pulsed-field gel electrophoresis (PFGE) method. National weekly report data were collected for investigating epidemiological trends.</p> <p>Results</p> <p>A total of 23 <it>emm </it>types were identified in 1,218 <it>S. pyogenes </it>isolates. The five most prevalent <it>emm </it>types were <it>emm</it>12 (50.4%), <it>emm</it>4 (23.2%), <it>emm</it>1 (16.4%), <it>emm</it>6 (3.8%) and <it>emm</it>22 (3.0%). PFGE analysis with <it>Sma</it>I suggested that, with a few exceptions, strains with a common <it>emm </it>type belonged to the same clone. There were two large <it>emm</it>12 clones, one with DNA resistant to cleavage by <it>Sma</it>I. Each prevalent <it>emm </it>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 <it>emm </it>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.</p> <p>Conclusion</p> <p>The occurrences of scarlet fever in central Taiwan in 2000–2006 were primarily caused by five <it>emm </it>types, which accounted for 96.8% of the isolates collected. Most of the <it>S. pyogenes </it>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 <it>emm </it>clones and to the SARS outbreak in 2003.</p