作者: YC
Agent
武漢肺炎(2019-nCoV)為一種新型的冠狀病毒，病毒結構有75%至80%與當年沙士(SARS)病毒的基因序列相同，並與多種蝙蝠冠狀病毒相類似。
The viral genome has been sequenced, and these results in conjunction with other reports show that it is 75 to 80% identical to the SARS-CoV and even more closely related to several bat coronaviruses
跟以往沙士(SARS)等冠狀病毒不同的是今次的武漢肺炎病毒比以往的冠狀病毒更會在人體的呼吸道的細胞滋長。
but notably, 2019-nCoV grows better in primary human airway epithelial cells than in standard tissue-culture cells, unlike SARS-CoV or MERS-CoV.
Risk
究竟武漢肺炎病毒對大眾的健康有多大風險？那就要從肺炎病毒的致病性(Pathogenicity)和傳染性(Transmissibility)解構。
以往沙士(SARS)等冠狀病毒主要感染肺部內的細胞，引致下呼吸道的衰竭。病毒主要是透過這些肺部受嚴重感染的患者傳染給他人，故此，在疫症後期，透過控制這些發病的帶菌者就可避免人傳人的風險。疫情的可控性因而提高，而疫症的傳染性亦相對降低。
Both SARS-CoV and MERS-CoV infect intrapulmonary epithelial cells more than cells of the upper airways. Consequently, transmission occurs primarily from patients with recognized illness and not from patients with mild, nonspecific signs.
從沙士等例子（圖1）可見，在沒有藥物對策下，病毒的致病性愈強，可控性愈高，傳染性愈低。（參考圖2）
按今次的武漢肺炎病患者的徵狀推斷，病患者大多出現上呼吸道感染徵狀，潛伏期達12-14日，亦有患者沒有發燒徵狀。當中以家庭單位(family cluster)的感染率達83%。在沒有發燒或其他嚴重徵狀下，病毒很可能已人傳人，令帶菌者更難以分辨。
如專家指出，在未知道武漢肺炎病毒的傳染性下，最高級別的應變是最好的防禦。因為若病毒對個人的致病性不高的話，受病毒感染的人就愈難察覺，在沒有任何病徵下，傳染性就愈高，對整個population的風險就愈高。
We currently do not know where 2019-nCoV falls on the scale of human-to-human transmissibility. But it is safe to assume that if this virus transmits efficiently, its seemingly lower pathogenicity as compared with SARS, possibly combined with super-spreader events in specific cases, could allow large-scale spread. In this manner, a virus that poses a low health threat on the individual level can pose a high risk on the population level, with the potential to cause disruptions of global public health systems and economic losses. This possibility warrants the current aggressive response aimed at tracing and diagnosing every infected patient and thereby breaking the transmission chain of 2019-nCoV.
雖然武漢肺炎病毒的致病性(Pathogenicity)沒有以往沙士(SARS)般強，受感染者很可能在沒有發燒等徵狀下無聲無色地人傳人，所以其傳染性(Transmissibility)不容小覷。
結語：No matter which side of scale it’s on, gear up with mask and maintain personal hygiene.
(如有錯漏，歡迎指正)
參考:
Huang C, Wang Y, Li X, et al. Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China. Lancet, January 24, 2020.
Chan JFW, Yuan SF, Kok KH, To KKW, Chu H, Yang J, et al. A familial cluster of pneumonia associated with the 2019 novel coronavirus indicating person-to-person transmission: a study of a family cluster. Lancet, January 24, 2020.
S Perlman. Another Decade, Another Coronavirus. New England Journal of Medicine, January 24, 2020.
VJ Munster, et al. A Novel Coronavirus Emerging in China — Key Questions for Impact Assessment, New England Journal of Medicine, January 24, 2020.
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