RESUMO
<p><b>OBJECTIVE</b>To understand the transmission mode of human infection with avian influenza A (H7N9) virus.</p><p><b>METHODS</b>Field epidemiological investigation was conducted for a family clustering of human infection with H7N9 virus in Hengxian county, Guangxi Zhuang Autonomous Region in February 2014. Two patients and their 82 close contacts were surveyed. The samples collected from the patients, environments and poultry were tested by using real time reverse transcriptase-polymerase chain reaction (rRT-PCR), and the samples from patients were used for virus isolation. The samples from 5 close contacts were tested with RT-PCR. The clinical data, exposure histories of the patients and the detection results of the isolates and their homology were analyzed.</p><p><b>RESULTS</b>Patient A became ill 4 days after her last exposure to poultry in Zhongshan, Guangdong province, and returned to her hometown in Hengxian 2 days after onset. Patient B was patient A's 5 years old son, who had no known exposure to poultry but slept with patient A for 4 days. He developed symptoms 4 days after last contact with his mother. Two strains of H7N9 virus were isolated from the two patients. The 2 isolates were highly homogenous (almost 100%) indicated by gene sequencing and phylogenetic tree. None of the other 81 close contacts developed symptoms of H7N9 virus infection.</p><p><b>CONCLUSION</b>Patients B was infected through close contact with patient A, indicating that avian H7N9 virus can spread from person to person, but the transmissibility is limited and non-sustainable.</p>