Descriptive Epidemiology and Trends of Human Infections with Avian Influenza A(H7N9) in Mainland China during the First Four Season

Objective: To describe the epidemiological characteristics of human infections with avian influenza A(H7N9) in mainland China during 2013--2016; to explore potential risk factors for death; and to examine whether these characteristics have changed in the first four seasons, in order to inform future prevention and control measures.;Methods: The surveillance case information on 766 cases of infection with A(H7N9) virus from 2013 to 2016 were obtained from the China CDC. Simple descriptive statistics were used to analyze basic epidemiological information, exposure factors, underlying medical conditions, antiviral treatment, and risk of death. Chi-square, Wilcoxon signed-rank and Cochran-Armitage trend tests were used to test the significance of difference between groups and 4-year trends. Logistic regression modeling was used to examine risk factors for death.;Results: Most human infections with A(H7N9) virus were males (69%), over 60 years old (40%), farmers, retirees and unemployed people (66%). Of all cases, 58% were exposed in the live poultry markets and 80% were exposed to poultry. The case mortality rate (CMR) was 41%. Most of the characteristics did not change over the four seasons. Multivariate analysis showed that older age in years (adjusted OR 1.04) and living in Anhui province (adjusted OR 2.26) were risk factors for death. Cases starting antiviral drugs within two days of illness onset (adjusted OR 0.47) or living in Fujian province (adjusted OR 0.48) were less likely to die. Only 10% of patients received antivirals within two days of illness onset.;Conclusion: More efforts are needed to decrease the incidence and CMR of elder people and to have more cases receive antivirals < 3 days after illness onset. Also, we need more information to explain the difference between the CMR in Anhui and Fujian provinces.