Objective  To investigate the epidemic characteristics of a family clustering of human infection with avian influenza A (H7N9) virus in Jiangxi province and to analyze the source and transmission mode of the infection.

  Methods  Two patients and their 57 close contacts were surveyed with a field investigation. The specimens sampled from the patients, close contacts and environment were tested by using real time reverse transcriptase-polymerase chain reaction (RT-PCR) and gene sequencing.

  Results  A 40 months old girls (the first case) and her 22 years old mother from Shangrao city of Jiangxi province were confirmed as avian influenza A (H7N9) virus infection on February 9 and 10, 2017. Both of the cases had a history of exposure to poultry before the incidence of the infection and the specimens collected from their residential environment were positive for avian influenza A (H7N9) virus. The phylogenetic tree analysis showed that the H7N9 virus strain isolated from the patients belonge to the Yangtze River Delta Lineage and is of low pathogenicity to birds. No abnormalities were observed during medical observation among all the close contacts of the girl patient, except for her mother with clinical symptoms 5 days after the occurrence of the girl's disease.

  Conclusion  The incidence of human avian influenza (H7N9) virus infection is a family clustering epidemic; the infection source for the first case could be the environment contaminated by the virus but there is no clear evidence for confirming the secondary infection being due to co-exposure to contaminated environment or limited human to human infection.