余宏傑課題組在禽流感H7N9病毒人際間傳播風險研究領域取得進展

復旦大學公共衛生學院余宏傑課題組在禽流感H7N9病毒人際間傳播風險研究領域取得進展，研究結果以「Assessment of Human-to-Human Transmissibility of Avian Influenza A(H7N9) Virus Across 5 Waves by Analyzing Clusters of Case Patients in Mainland China, 2013–2017」為題於近期發表在Clinical Infectious Diseases(IF 9.12)（論文鏈接：https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciy541/5046928）。

自2013年3月中國發現了全球首例人感染禽流感H7N9病例以來，每年冬春季都會出現一波人感染禽流感H7N9疫情。該病毒可通過基因重配或適應性突變演變成為引起流感大流行的病毒，持續的病毒學和流行病學研究是大流行風險評估的重要內容。

2016-2017年第五波疫情前，H7N9病毒為低致病性禽流感病毒。2017年初，有研究報道，少數人感染禽流感H7N9病例中所分離病毒的HA裂解位點插入了多個鹼性氨基酸，提示該病毒已變異為高致病性禽流感病毒。2016-2017年第五波疫情較往年出現的早，地理擴散範圍更廣，報告的病例數也超過了前四波。因此，第五波疫情中，禽流感H7N9病毒在人與人之間的傳播風險是否增強成為尚待解決的科學問題。

本研究通過分析聚集性H7N9疫情的流行病學參數的變化，定量評估H7N9病毒人際間的傳播風險是否發生了變化。研究發現，報告的聚集性病例的發病時間分布與散發病例相似。聚集性H7N9疫情的中位病例數為2，最大為3。所有聚集性H7N9疫情的人際傳播均未超過2代。與沒有血緣關係的親屬相比，有血緣關係的感染禽流感H7N9的相對危險度為1.65（95%置信區間：0.88-3.09），但無統計學差異。假設具有相同的易感性，統計模擬的結果顯示，當聚集性H7N9病例佔全部病例5.6%時，暴露後人感染禽流感H7N9的風險為4.2%（圖A）。禽流感H7N9病毒有效繁殖數上限為0.12（95%置信區間：0.10-0.14），各波次間無統計學差異（χ2 = 1.52, p=0.822）（圖B）。

圖：五波人感染禽流感H7N9疫情中，感染髮病的風險及有效繁殖數上限估計值

（A：聚集性病例佔比與感染風險；B：有效繁殖數上限估計值）

Abstract

Background

The 2016–17 epidemic of human infections with avian influenza A(H7N9) virus was alarming, due to the surge in reported cases across a wide geographic area and the emergence of highly-pathogenic A(H7N9) viruses. Our study aimed to assess whether the human-to-human transmission risk of A(H7N9) virus has changed across the 5 waves since 2013.

Methods

Data on human cases and clusters of A(H7N9) virus infection were collected from the World Health Organization, open access national and provincial reports, informal online sources, and published literature. We compared the epidemiological characteristics of sporadic and cluster cases, estimated the relative risk (RR) of infection in blood relatives and non–blood relatives, and estimated the bounds on the effective reproductive number (Re) across waves from 2013 through September 2017.

Results

We identified 40 human clusters of A(H7N9) virus infection, with a median cluster size of 2 (range 2–3). The overall RR of infection in blood relatives versus non–blood relatives was 1.65 (95% confidence interval [CI]: 0.88, 3.09), and was not significantly different across waves (χ2 = 2.66, P = .617). The upper limit of Re for A(H7N9) virus was 0.12 (95% CI: 0.10, 0.14) and was not significantly different across waves (χ2 = 1.52, P = .822).

Conclusions

The small cluster size and low Re suggest that human-to-human transmissibility of A(H7N9) virus has not changed over time and remains limited to date. Continuous assessment of A(H7N9) virus infections and human case clusters is of crucial importance for public health.

來源：復旦大學公共衛生學院

本期編輯：Tony

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