On 31 March 2013, Chinese authorities announced the identification of a novel reassortant A(H7N9) influenza virus isolated from three unlinked fatal cases of severe respiratory disease in eastern China; two in Shanghai and one in Anhui province. The WHO Collaborating Centre for Reference and Research on Influenza at the Chinese Center for Disease Control and Prevention (CCDC) had subtyped and sequenced the viruses; they were found to be almost identical and considered to be of low-pathogenic avian origin. This is the first time that human infection with avian influenza virus A(H7N9) has been identified. This is also the first time that a low-pathogenic avian virus caused lethal human infections. Since then, human cases have continued to be reported, and as of 1 May, there were 128 laboratory-confirmed cases, including 26 deaths reported from eight neighbouring provinces (Anhui, Fujian, Henan, Hunan, Jiangsu, Jiangxi, Shandong, and Zhejiang) and two municipalities (Beijing and Shanghai). One case who acquired his infection in Jiangsu travelled to Taiwan before developing illness. A few small clusters were detected but almost all cases have occurred sporadically, without obvious epidemiological links. While occasional human-to-human transmission in the clusters cannot be ruled out, there is certainly no confirmed sustained human-to-human transmission. A few mild cases have been detected. Outside the clusters, more than 3000 contacts of the cases were traced, which did not lead to the detection o
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