Epidemiology of Avian Influenza a H7N9 Virus in Human Beings Across Five Epidemics in Mainland China, 2013-17: An Epidemiological Study of Laboratory-Confirmed Case Series

        Background

        The avian influenza A H7N9 virus has caused infections in human beings in China since 2013. A large epidemic in 2016-17 prompted concerns that the epidemiology of the virus might have changed, increasing the threat of a pandemic. We aimed to describe the epidemiological characteristics, clinical severity, and time-to-event distributions of patients infected with A H7N9 in the 2016-17 epidemic compared with previous epidemics.

        背景：中国自2013年发现了第一例感染。在2016-17曾出现一个大的疫情年，大家担心这种病毒的流行病学可能已经改变了，存在越来越多的大流行威胁。此研究描述人类禽流感H7N9病毒流行病学特点、临床严重程度，以及比较2016-2017年与之前感染了H7N9疫情患者流行病事件分布。

        Methods

        In this epidemiological study, we obtained information about all laboratory-confirmed human cases of A H7N9 virus infection reported in mainland China as of Feb 23, 2017, from an integrated electronic database managed by the China Center for Disease Control and Prevention (CDC) and provincial CDCs. Every identified human case of A H7N9 virus infection was required to be reported to China CDC within 24 h via a national surveillance system for notifiable infectious diseases. We described the epidemiological characteristics across epidemics, and estimated the risk of death, mechanical ventilation, and admission to the intensive care unit for patients admitted to hospital for routine clinical practice rather than for isolation purpose. We estimated the incubation periods, and time delays from illness onset to hospital admission, illness onset to initiation of antiviral treatment, and hospital admission to death or discharge using survival analysis techniques.

        方法：在流行病学研究中，我们收集由中国疾病预防控制中心(CDC)和省疾病预防控制中心管理提供的，截至到2017年2月23日为止所有中国大陆实验室证实的人类感染H7N9病毒的病例。每例感染H7N9病毒的病人需在24小时内通过法定传染病国家监测系统上报中国疾病预防控制中心。该研究描述了H7N9病毒感染的流行病学特征，并估算了住院病人接受常规临床治疗的死亡风险、机械通气和入院ICU的风险而不是仅为隔离风险考虑。由此我们利用生存分析推算潜伏期、从发病到入院及从发病至开始抗病毒治疗的时间间隔，以及住院至死亡或出院的时间。

        Findings

        Between Feb 19, 2013, and Feb 23, 2017, 1220 laboratory-confirmed human infections with A H7N9 virus were reported in mainland China, with 134 cases reported in the spring of 2013, 306 in 2013-14, 219 in 2014-15, 114 in 2015-16, and 447 in 2016-17. The 2016-17 A H7N9 epidemic began earlier, spread to more districts and counties in affected provinces, and had more confirmed cases than previous epidemics. The proportion of cases in middle-aged adults increased steadily from 41% (55 of 134) to 57% (254 of 447) from the first epidemic to the 2016-17 epidemic. Proportions of cases in semi-urban and rural residents in the 2015-16 and 2016-17 epidemics (63% [72 of 114] and 61% [274 of 447], respectively) were higher than those in the first three epidemics (39% [52 of 134], 55% [169 of 306], and 56% [122 of 219], respectively). The clinical severity of individuals admitted to hospital in the 2016-17 epidemic was similar to that in the previous epidemics.

        结果：2013年2月19日—2017年2月23日，在中国大陆的报道了1220例实验室确诊的人感染H7N9病毒病例，2013年春季134例, 在2013-14年306例，2014-15年219例，2015-16年114例，2016-17年447例。在2016-17年 H7N9疫情开始的更早，蔓延到更多的省份和区县，并比以往年份有更多的患病病人。中年人的患病比例从最开始流行的41%(55/134)稳步增加至2016-17年的57%(254/447)。在2015-16年和2016-17年城市郊区和农村居民的患病比例(分别63% 和61%)均高于前三个流行期(分别为39% ，55% 和56%)。在2016-17年发病的入院临床严重程度与以往年份相似。

        Interpretation

        Age distribution and case sources have changed gradually across epidemics since 2013, while clinical severity has not changed substantially. Continued vigilance and sustained intensive control efforts are needed to minimise the risk of human infection with A H7N9 virus.

        解释：自2013以来，H7N9的流行年龄分布和流行特点逐渐改变，而临床严重程度没有发生实质性变化。需要继续警惕和持续加强控制工作，以尽量减少人感染H7N9病毒的风险。

        翻译：张雅芝

        审校：曹广慧