emm1 increases in scarlet fever outbreaks

Large outbreaks of scarlet fever caused by emm12 group A Streptococcus (GAS) occurred in China in 2011. Since then, scarlet fever has been epidemic annually, but there are no continuous surveillance data on the molecular epidemiological characterization of the GAS isolates. This study aimed to figure out the dynamic prevalence and diversity of GAS population and to explore the pathogen-associated spread mechanism. Epidemiological data of scarlet fever in Shanghai during 2011–2015 were obtained from the National Notifiable Infectious Disease Surveillance System. Throat swabs of patients with scarlet fever were cultured, and GAS carriage surveillance was performed in schools. A total of 1,568 GAS isolates were collected for analysis, and 39 emm1 isolates were performed Illumina sequencing. This continuous study showed that the annual incidence of culture-confirmed scarlet fever was 7.5-19.4/100,000-person-year in Shanghai during 2011-2015, with an average GAS carriage rate being 7.6% in school-age children. With predominance of emm12 (61.8%, 897/1451) in patient isolates, the proportion of emm1 GAS strains increased from 3.8% in 2011 to 48.6% in 2014, and they harbored a superantigen profile different from emm12 isolates. Two predominant clones, SH001-emm12 and SH002-emm1, circulated in 66.9% of scarlet fever cases and 50% of carriers. GAS isolates showed high frequencies (>95%) of resistance to macrolides (ermB) and tetracycline (tetM). Genomic analysis showed emm1 isolates in China constituted distinct clads, harboring characteristic mobile genetic elements. GAS population causing scarlet fever in China is changing. Ongoing surveillance is warranted to monitor the dynamic changes of GAS emm type, predominant clone, and superantigen profile.

2011年中国暴发了由emm12型A群链球菌（group A Streptococcus, GAS）引起的大规模猩红热疫情。自此之后，猩红热每年均呈流行态势，但目前尚无关于GAS分离株分子流行病学特征的连续监测数据。本研究旨在明确GAS种群的动态流行与多样性特征，并探究病原体相关的传播机制。研究获取了2011–2015年上海市猩红热的流行病学数据，数据来源于国家法定传染病监测系统。研究人员对猩红热患者的咽拭子进行培养，并在学校内开展GAS携带状况监测。本研究共收集1568株GAS分离株用于分析，其中39株emm1型分离株采用Illumina测序技术进行测序。本连续性研究显示，2011–2015年上海市经培养确认的猩红热年发病率为7.5~19.4/10万人年，学龄儿童的GAS平均携带率为7.6%。患者分离株中以emm12型占比最高（61.8%，897/1451），而emm1型GAS菌株的占比从2011年的3.8%升至2014年的48.6%，且其携带的超抗原谱与emm12型分离株存在差异。两种优势克隆株——SH001-emm12与SH002-emm1——分别在66.9%的猩红热病例以及50%的携带者中流行。GAS分离株对大环内酯类抗生素（ermB介导）及四环素类抗生素（tetM介导）呈现高耐药性（耐药率>95%）。基因组分析显示，中国的emm1型GAS分离株构成了独特的进化簇，携带有特征性的移动遗传元件。中国引发猩红热的GAS种群正发生演变，需开展持续监测以跟踪GAS血清型、优势克隆株及超抗原谱的动态变化。