Clinical severity of human infections with avian influenza A(H7N9) virus, China, 2013/14

L Feng; J T Wu; X Liu; P Yang; T K Tsang; H Jiang; P Wu; J Yang; V J Fang; Y Qin; E H Lau; M Li; J Zheng; Z Peng; Y Xie; Q Wang; Z Li; G M Leung; G F Gao; H Yu; B J Cowling

doi:10.2807/1560-7917.ES2014.19.49.20984

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Clinical severity of human infections with avian influenza A(H7N9) virus, China, 2013/14
L Feng^1,2 , J T Wu^2,3 , X Liu^2,4 , P Yang^2,5 , T K Tsang³ , H Jiang¹ , P Wu³ , J Yang¹ , V J Fang³ , Y Qin¹ , E H Lau³ , M Li¹ , J Zheng¹ , Z Peng¹ , Y Xie⁴ , Q Wang⁵ , Z Li¹ , G M Leung³ , G F Gao^6,7 , H Yu¹ , B J Cowling³
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Affiliations: ¹ Division of Infectious Disease, Key Laboratory of Surveillance and Early-warning on Infectious Disease, Chinese Center for Disease Control and Prevention (China CDC), Beijing, China ² These authors contributed equally to this work ³ School of Public Health, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong Special Administrative Region, China ⁴ Jiangxi Provincial Centre for Disease Control and Prevention, Nanchang, Jiangxi Province, China ⁵ Beijing Center for Disease Prevention and Control; and Beijing Research Center for Preventive Medicine, Beijing, China ⁶ CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China ⁷ Office of Director-General, Chinese Center for Disease Control and Prevention (China CDC), Beijing, China

Correspondence:
H Yu
yuhj chinacdc.cn
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Citation style for this article: Feng L, Wu J T, Liu X, Yang P, Tsang T K, Jiang H, Wu P, Yang J, Fang V J, Qin Y, Lau E H, Li M, Zheng J, Peng Z, Xie Y, Wang Q, Li Z, Leung G M, Gao G F, Yu H, Cowling B J. Clinical severity of human infections with avian influenza A(H7N9) virus, China, 2013/14. Euro Surveill. 2014;19(49):pii=20984. https://doi.org/10.2807/1560-7917.ES2014.19.49.20984 Received: 18 Jun 2014

Abstract

Assessing the severity of emerging infections is challenging because of potential biases in case ascertainment. The first human case of infection with influenza A(H7N9) virus was identified in China in March 2013; since then, the virus has caused two epidemic waves in the country. There were 134 laboratory-confirmed cases detected in the first epidemic wave from January to September 2013. In the second epidemic wave of human infections with avian influenza A(H7N9) virus in China from October 2013 to October 2014, we estimated that the risk of death among hospitalised cases of infection with influenza A(H7N9) virus was 48% (95% credibility interval: 42-54%), slightly higher than the corresponding risk in the first wave. Age-specific risks of death among hospitalised cases were also significantly higher in the second wave. Using data on symptomatic cases identified through national sentinel influenza-like illness surveillance, we estimated that the risk of death among symptomatic cases of infection with influenza A(H7N9) virus was 0.10% (95% credibility interval: 0.029-3.6%), which was similar to previous estimates for the first epidemic wave of human infections with influenza A(H7N9) virus in 2013. An increase in the risk of death among hospitalised cases in the second wave could be real because of changes in the virus, because of seasonal changes in host susceptibility to severe infection, or because of variation in treatment practices between hospitals, while the increase could be artefactual because of changes in ascertainment of cases in different areas at different times. .