自2013年3月中国首次发现新型禽流感病毒H7N9以来，其于2013—2014年期间发生流行，2015年也有散发性感染。该病毒的流行不仅危及家禽养殖业，还对公共卫生安全造成严重威胁。为调查活禽市场中H7N9的进化史和季节性变化，本研究于2013年7—12月在H7N9主要流行地区之一江苏省苏州市活禽市场采集2 655份鸡、鸭咽拭子样本，对样本中流感病毒核酸进行检测。结果显示，冬季样本中H7N9阳性率显著高于夏季样本，同时发现样本中存在H5、H7和H9亚型毒株之间的混合感染。进一步对H7N9阳性样本的HA、NA和PB2基因序列进行分析，结果表明阳性样本中HA、NA和PB2基因序列与新型H7N9病毒的相应基因序列同源，其在家禽体内传代时也在继续进化。特别是一些样品中PB2基因序列与H5N1病毒PB2基因序列的同源性较高。结果提示，苏州存在一种新型H7N9病毒基因重排的可能性，建议在活禽市场对所有禽流感病毒亚型进行持续监控，从而有助于流感病毒的及时防控。

A novel avian influenza A (H7N9) virus has caused epidemics during 2013 to 2014, and sporadic infections in 2015. To investigate the evolutionary history and seasonal variations of H7N9 in live poultry markets (LPMs), 2 655 pharyngeal swabs of chickens and ducks were collected from July to December 2013 in Suzhou, Jiangsu Province, China, which was one of the major epidemic areas in 2013. The results showed that the positive rate in winter was higher than that in summer and there were mixed infections among H5, H7, and H9 strains, suggesting the occurrence of multiple reassortment events. The HA, NA and PB2 genes from selected H7N9-positive samples were then sequenced to trace the evolutionary history of the novel H7N9 virus. Phylogenetic analysis revealed that all Suzhou isolates in this study were clustered around the novel H7N9 virus, but they also continued to evolve while circulating in the poultry. In fact, the PB2 gene of some sequenced samples was closely related to H5N1. This study identifies the genetic reassortment of a novel H7N9 virus in Suzhou and suggests that constant surveillance of all avian influenza virus subtypes in LPMs will help to track the source of newly emerging virulent viral strains.