CNN News: 病毒如何傳播

How does a virus spread? There are plenty of ways. It could be - - a sneeze, a handshake, to name a few.

病毒是如何傳播的?有很多方法。它可能是——一個噴嚏，一次握手，等等。

Then there's our habits -- washing our hands, not touching our face. Even the climate may play a role in determining how far and how fast an infection spreads.

還有我們的習慣——洗手，不摸臉。氣候也可能在決定感染傳播的距離和速度方面發(fā)揮作用。

Scientists have summed up how far an infection can spread with a number. It's called R0. A number greater than one indicates it'll grow, less than one indicates the outbreak will die out.

科學家們已經用數字總結出傳染病可以傳播多遠。它叫做R0。大于1的數字表示疫情會擴大，小于1的數字表示疫情會消失。

Scientists determine the number with a formula that brings together all the environmental and biological factors.

科學家們將所有的環(huán)境和生物因素結合在一起，得出了這個數字。

This is how it looks in reality -- an infection is introduced to human from animal, let's say, the bigger the R0 number, the more people of virus can infect. So an R0 of two means that patients zero will on average infect two other people who in turn can infect another two people and so on.

這是在現實中的樣子——假設感染從動物被引入到人類，R0值越大，病毒感染的人就越多。R0等于2意味著患者0平均會感染另外兩個人，而這兩個人又會感染另外兩個人，以此類推。

An infection like measles sits higher of the spectrum with an R0 of between 12 and 18.

麻疹等感染的R0值在12到18之間，處于較高的范圍。

At the lower end is something like Ebola with an R0 number of 1.5 to 2.5.

較低的是埃博拉病毒，R0值為1.5到2.5。

And while the flu varies from year to year, one study reports it averages to 1.2.

雖然流感每年都一樣，但一項研究報告稱，平均每年有1.2人感染。

But as various factors change, so too does the R0. Take SARS. When it first emerged, SARS spread rapidly with a high R0, but people were only contagious once symptoms started showing. Once people were informed about the symptoms, they started coming to the hospital earlier. People could check themselves into hospital before infecting other people, pushing the R0 number below one.

但是隨著各種因素的變化，R0也在變化。當SARS剛出現時，它以高數值R0迅速傳播，但人們只有在癥狀開始出現時才知道它具有傳染性。一旦被告知這些癥狀，們可以在感染他人之前先到醫(yī)院檢查，將R0數值壓到1以下。

And that is how a virus can spread.

這就是病毒傳播的方式。