As many as 20,000 viruses are expelled in an average cough, which may be sufficient to infect many people - particularly those who are not vaccinated.

Julian Tang, a consultant at Singapore's National University Hospital's Division of Microbiology, said as many as 3,000 tiny droplets are produced in a standard cough.

Using previous research on influenza viral loads in nasal secretions, and assuming that each coughed airborne droplet measures between 1 to 5 micrometers in diameter, that adds up to many, many viruses in a single cough.

"Based on this research and assuming about 3,000 droplets are produced per cough, this range of influenza viruses produced per cough is about 195 to 19,500," Tang said.

He added that this figure of 3,000 droplets refers to those that remain suspended in the air for considerable periods - long enough to infect people.

" Larger droplets carrying influenza viruses may also be produced during a cough, but these will fall to the ground relatively quickly and will no longer be considered to be significant in the airborne transmission of influenza," he said.

With a new N1N1 influenza virus spreading around the world, governments in many countries have revived advertisements entreating people to observe personal hygiene.

However, experts are uncertain as to what constitutes an infective dose when it comes to influenza viruses.

But as a guide, previous research has found that it takes just one to 10 organisms to cause viral hemorrhagic fevers, and 10 to 100 organisms to cause viral encephalitis.

今后你咳嗽或打喷嚏时，就有充分的理由捂住嘴了。

据统计，每咳嗽一次平均会释放多达2万个病毒，这足以让很多人感染——尤其是那些没有进行预防接种的人。

新加坡国立大学附属医院微生物科的顾问Julian Tang说，一次普通的咳嗽能产生3000个微滴。

根据此前有关鼻腔分泌物中流感病毒载量的研究，并假设每个咳出的通过空气传播的微滴的直径在1至5微米之间，那么一次咳嗽产生的病毒量就非常之多。

Julian Tang说：“根据该研究，并假设每次咳嗽会产生约三千个微滴，那么一次咳嗽产生的流感病毒量约在195到19500个之间。”

他说，这三千个微滴指的是那些长时间悬浮在空气中微滴——它们存留在空气中的时间足以感染人群。

他说：“咳嗽可能也会产生较大的携带流感病毒的微滴，但这些微滴会相对较快地落到地上，所以对流感在空气中的传播几乎不起作用。”

眼下一种新型的N1H1流感病毒正在全球广泛传播，很多国家的政府纷纷重新打出广告，提醒人们注意个人卫生。

然而，专家们也不能确定多少流感病毒能让人感染。

但此前的研究发现，仅1至10个微生物体就可导致病毒出血热，10至100个微生物即可导致病毒性脑炎，这可作为一个参考。