Epidemiological characteristics of human avian influenza A (H7N9) virus infection in China

To investigate the epidemiological characteristics of human infections with avian influenza A (H7N9) in China and to provide scientific evidence for the adjustment of preventive strategy and control measures.Demographic and epidemiologic information on human cases were collected from both reported data of field epidemiological investigation and the reporting system for infectious diseases.A total of 433 cases including 163 deaths were reported in mainland China before June 4, 2014. Two obvious epidemic peaks were noticed, in March to April, 2013 and January to February, 2014. Confirmed cases emerged in 14 areas of China. Five provinces, including Zhejiang, Guangdong, Jiangsu, Shanghai, and Hunan, reported about 85% of the total cases. Median age of the confirmed cases was 58 years (range, 1-91), with 70% as males. Of the 418 cases with available data, 87% had ever exposed to live poultry or contaminated environments. 14 clusters were identified but human to human transmission could not be ruled out in 9 clusters.Human infections with avian influenza A (H7N9) virus showed the characteristics of obvious seasonal distribution, with certain regional clusters. The majority of confirmed cases were among the elderly, with more males seen than the females. Data showed that main source of infection was live poultry and the live poultry market had played a significant role in the transmission of the virus.