Epidemiology of human infection with avian influenza A (H7N9) virus and environmental virus surveillance in Shaoxing, Zhejiang

Objective To understand the epidemiological characteristics of human infection with avian influenza A (H7N9) virus and the distribution of H7N9 virus in environment in Shaoxing, Zhejiang province, and provide evidence for the prevention and control of human infection with (H7N9) virus. Methods Descriptive epidemiological analysis was conducted on the incidence data of human infection with H7N9 virus from April 2013 to April 2014 and the surveillance data of (H7N9) virus in environment in Shaoxing. The statistical analysis was conducted with Fisher's Exact Test, Pearson Chi-Square, and Two independent sample t-test. Results Fourteen cases of human infection with H7N9 were confirmed, including 7 deaths (50%). Among the confirmed cases, nine were males (64.29%), eleven were aged 50 years (78.57%), and 13 had alive poultry exposure histories (92.86%). H7N9 viruses were detected in the samples collected from the environments around 6 confirmed cases. The mean interval was 7.071.73 days between onset and diagnosis and 16.0015.21 days between onset and death. A total of 530 environmental samples, including those from alive poultry, were collected in 2013, the detection rate of H7N9 virus was 1.51%, and 745 environmental samples, including those from alive poultry, were collected in 2014, the detection rate of H7N9 was 16.11%, the difference was statistical significant (2=61.37,P0.001). The positive detection rate of H7N9 virus in outer environment was correlated with the time distribution of human infection cases. Conclusion Human infection with H7N9 virus mainly occurred in males and old people. The detection results of chicken throat swabs and cutting board/cage smears can be used as sensitive indicators in outer environment surveillance for the early warning and prevention of human H7N9 infection outbreak.