Comment: Timely estimates of influenza A H7N9 infection severity [Articles]

The Lancet  
Jul 13, 2013  Volume 382  Number 9887  p101 – 180

Timely estimates of influenza A H7N9 infection severity
Cécile Viboud, Lone Simonsen
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WHO guidance, released in May, 2013, established that estimates of disease severity are key for risk assessment of novel influenza viruses.1 Unfortunately, epidemiological assessment of severity is difficult in the context of an emerging disease, when estimates are most needed to guide pandemic response. The case fatality risk is an estimate of the proportion of patients with a specific disease who have died; however, both the numerator and denominator of this estimator are elusive.2–4 Case detection is typically skewed towards patients with severe disease; laboratory-based case ascertainment can vary geographically and temporally; and there are delays between onset, death, and reporting, potentially leading to overestimation or underestimation of fatality risk.

Comparative epidemiology of human infections with avian influenza A H7N9 and H5N1 viruses in China: a population-based study of laboratory-confirmed cases
Benjamin J Cowling, Lianmei Jin, Eric HY Lau, Qiaohong Liao, Peng Wu, Hui Jiang, Tim K Tsang, Jiandong Zheng, Vicky J Fang, Zhaorui Chang, Michael Y Ni, Qian Zhang, Dennis KM Ip, Jianxing Yu, Yu Li, Liping Wang, Wenxiao Tu, Ling Meng, Joseph T Wu, Huiming Luo, Qun Li, Yuelong Shu, Zhongjie Li, Zijian Feng, Weizhong Yang, Yu Wang, Gabriel M Leung, Hongjie Yu
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The sex ratios in urban compared with rural cases are consistent with exposure to poultry driving the risk of infection—a higher risk in men was only recorded in urban areas but not in rural areas, and the increased risk for men was of a similar magnitude for H7N9 and H5N1. However, the difference in susceptibility to serious illness with the two different viruses remains unexplained, since most cases of H7N9 were in older adults whereas most cases of H5N1 were in younger people. A limitation of our study is that we compared laboratory-confirmed cases of H7N9 and H5N1 infection, and some infections might not have been ascertained.

Human infection with avian influenza A H7N9 virus: an assessment of clinical severity
Hongjie Yu, Benjamin J Cowling, Luzhao Feng, Eric HY Lau, Qiaohong Liao, Tim K Tsang, Zhibin Peng, Peng Wu, Fengfeng Liu, Vicky J Fang, Honglong Zhang, Ming Li, Lingjia Zeng, Zhen Xu, Zhongjie Li, Huiming Luo, Qun Li, Zijian Feng, Bin Cao, Weizhong Yang, Joseph T Wu, Yu Wang, Gabriel M Leung
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Human infections with avian influenza A H7N9 virus seem to be less serious than has been previously reported. Many mild cases might already have occurred. Continued vigilance and sustained intensive control efforts are needed to minimise the risk of human infection.