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Study Question: Can avian influenza A (H7N9) virus be transmitted between unrelated individuals in a hospital setting?, Methods: An epidemiological investigation looked at two patients who shared a hospital ward in February 2015, in Quzhou, Zhejiang Province, China. Samples from the patients, close contacts, and local environments were examined by real time reverse transcriptase (rRT) polymerase chain reaction (PCR) and viral culture. Haemagglutination inhibition and microneutralisation assays were used to detect specific antibodies to the viruses. Primary outcomes were clinical data, infection source tracing, phylogenetic tree analysis, and serological results., Study Answer and Limitations: A 49 year old man (index patient) became ill seven days after visiting a live poultry market. A 57 year old man (second patient), with a history of chronic obstructive pulmonary disease, developed influenza-like symptoms after sharing the same hospital ward as the index patient for five days. The second patient had not visited any poultry markets nor had any contact with poultry or birds within 15 days before the onset of illness. H7N9 virus was identified in the two patients, who both later died. Genome sequences of the virus isolated from both patients were nearly identical, and genetically similar to the virus isolated from the live poultry market. No specific antibodies were detected among 38 close contacts. Transmission between the patients remains unclear, owing to the lack of samples collected from their shared hospital ward. Although several environmental swabs were positive for H7N9 by rRT-PCR, no virus was cultured. Owing to delayed diagnosis and frequent hospital transfers, no serum samples were collected from the patients, and antibodies to H7N9 viruses could not be tested., What This Study Adds: Nosocomial H7N9 transmission might be possible between two unrelated individuals. Surveillance on patients with influenza-like illness in hospitals as well as chickens in live poultry markets should be enhanced to monitor transmissibility and pathogenicity of the virus., Funding, Competing Interests, Data Sharing: Funding support from the Program of International Science and Technology Cooperation of China (2013DFA30800), Basic Work on Special Program for Science and Technology Research (2013FY114600), National Natural Science Foundation of China (81402730), Special Program for Prevention and Control of Infectious Diseases in China (2013ZX10004218), US National Institutes of Health (1R01-AI108993), Zhejiang Province Major Science and Technology Program (2014C03039), and Quzhou Science and Technology Program (20111084). The authors declare no other interests and have no additional data., (© Fang et al 2015.)