值得重视的气溶胶传播说
Important aerosol propagation theory
682字
2021-01-12 16:40
57阅读
火星译客

How does coronavirus spread? Scientists are increasingly convinced that airborne transmission plays a role. Last week, more than 200 specialists penned an open letter to the World Health Organization urging it to officially accept that the Covid-19 virus can spread through the air further than social distancing recommendations.

新型冠状病毒是如何传播的?科学家们越来越确信,空气传播在其中发挥了作用。上周(去年7月上旬),逾200名专家联名向世界卫生组织(WHO)发出了一封公-开-信,敦促其正式承认,新冠病毒可以通过空气传播且传播距离大于社交疏离规定中建议的距离。

The WHO says the possibility cannot be ruled out but its reluctance so far to embrace airborne transmission has put it at odds with aerosol chemists and engineers, who now believe the virus can spread through tiny particles that stay aloft for hours on air currents, in addition to the usual accepted route of larger droplets of saliva and mucus sprayed out from coughs and sneezes. The tension highlights the dilemma of using incomplete and potentially outdated scientific evidence to make critical judgment calls in a rapidly changing situation.

世卫组织表示,不能排除这种可能性。但该组织至今不情愿接受空气传播的说法,这使它与研究气溶胶的化学家和工程师产生了分歧。这些研究者现在认为,除了经由咳嗽和打喷嚏时喷出的较大唾液和粘液飞沫传播这一通常公认的传播途径之外,新冠病毒还能够通过可以在气流中悬浮数小时的微小颗粒进行传播。世卫组织与研究者之间的这种紧张突显出,要在快速变化的形势下依据不完整和可能过时的科学证据做出关键性判断,存在一种窘境。

The virus is worryingly contagious, with nearly 13m confirmed cases worldwide. Droplets (defined as particles at least 5-10 microns across) are widely regarded as the master key to respiratory infection. They can be expelled in coughs and sneezes, as well as by singing, shouting and talking. Due to gravity, droplets generally fall to the floor within several metres — hence the need for distancing. Infection can occur directly, when virus-laden droplets enter the eyes, mouth or nose of another person, or indirectly, when a person touches a surface on which droplets have fallen and then transfers the virus to their own eyes, mouth or nose, which explains handwashing guidance.

新冠病毒具有令人担忧的传染性,全世界已有近1300万确诊病例。外界广泛认为,飞沫(定义为直径至少5-10微米的颗粒)是呼吸道感染的主要原因。这种飞沫可以通过咳嗽和打喷嚏喷出,也可以通过唱歌、喊叫和交谈产生。由于重力作用,飞沫一般会在几米内落到地上,这就解释了为何需要保持社交距离。当携带病毒的飞沫进入他人的眼睛、嘴巴或是鼻子时,会造成直接感染,而当携带病毒的飞沫落到物体表面,而某人接触了这些表面并随即将病毒带入自己的眼睛、嘴巴或鼻子时,会造成间接感染,后者解释了卫生指导意见要求我们洗手的原因。

But the appearance of large infection clusters at indoor gatherings has led many experts, such as Kimberly Prather, an atmospheric chemist at the University of California, San Diego, to question whether droplets explain everything. For some cases, she told Nature, the only way to explain certain transmission clusters is “you put it in the air and everyone breathes that air”.

但是在室内聚会中出现的大规模聚集性感染使得许多专家——如加利福尼亚大学圣迭戈分校(University of California, San Diego)的大气化学家金伯莉•普拉瑟(Kimberly Prather)——开始质疑飞沫是否可以解释一切。她向《自然》(Nature)杂志表示,在一些情况下,某些聚集性感染事件的唯一解释是“你将它放入了空气中,所有人都呼吸了这种空气”。

Airborne spread involves particles that are smaller than droplets, called aerosols (also called droplet nuclei or microdroplets). These fine particles, smaller than 5 microns, can be emitted in the same way that droplets are, but also by breathing. They linger in the air, where they can be inhaled by others. Last month, Prof Prather argued for the aerosol transmission of viruses to be “acknowledged as a key factor in the spread of infectious respiratory diseases”, with implications for indoor mask-wearing, ventilation and crowding, as well as wider testing.

空气传播涉及到比飞沫更小的颗粒,称为气溶胶(也称为飞沫核或微滴)。这些小于5微米的细小颗粒可以像飞沫一样喷出,也可以通过呼吸排出。它们悬浮在空气中,可以被他人吸入。上月,普拉瑟教授表示,病毒的气溶胶传播“作为传染性呼吸道疾病传播的一个关键因素应得到承认”,这对室内佩戴口罩、通风、聚集,以及更广泛的测试都具有影响。

A patchwork of studies can indeed be pieced together into plausible scenarios of airborne infection. People produce clouds of aerosols when they breathe and talk; some individuals are “superemitters”, exhaling particularly large clouds; aerosols can remain buoyant for hours; research from the 2002-2003 Sars outbreak show aerosols can contain an infectious virus. Interestingly, airborne transmission may explain some perplexing superspreading events when distancing and hygiene rules were followed. One restaurant outbreak was traced back to an air conditioning unit.

确实可以用一些零散的研究拼凑出空气传播的合理情景。人们在呼吸和交谈时会产生气溶胶云;有些人是“超级喷射者”,会呼出特别大的气溶胶云;气溶胶可以在空中飘浮数小时;2002-03年“非典”(SARS)爆发时的研究表明,气溶胶可能含有一种传染性病毒。有趣的是,在相关人员遵循了社交距离和卫生规定的情况下,空气传播或许能够解释一些令人困惑的超级传播事件。一家餐厅爆发感染事件的原因就可以追溯到一个空调设备。

Other observations provide circumstantial support: asymptomatic and pre-symptomatic spreaders do not, by definition, sneeze or cough appreciably and yet are known to transmit the virus to others. Aerosols might be even more dangerous than droplets: smaller particles can potentially penetrate deeper into the airways, possibly bypassing the immune system and causing more severe disease.

其他观察结果提供了间接的支持:根据对于传播者的定义,无症状和出现症状前的传播者不会打喷嚏或咳嗽,但我们已知他们会将病毒传播给他人。气溶胶可能比飞沫更加危险:更小的颗粒有可能进入呼吸道的更深处,可能绕过免疫系统,导致更严重的疾病。

For now, the WHO maintains that only “aerosol-generating procedures” in medical settings, such as the insertion of breathing tubes, are proven to spread Covid-19 through the air. But it agreed last week that more research is needed. Prof Prather points out that some of the science guiding today's advice was gathered in the 1930s, and requires updating; others complain that the bar for admitting new evidence is set too high.

目前,世卫组织坚持认为,只有医疗环境下的“气溶胶产生程序”,如气管插管,被证实可以通过空气传播新冠病毒。但该组织上周同意,需要进行更多的研究。普拉瑟教授指出,对如今卫生建议进行指导的是上世纪30年代总结得出的一些科学观点,需要进行更新;其他人则抱怨称,承认新的科学证据的门槛设定得太高了。

The current uncertainty over airborne spread mirrors the international debate about masks. An anxious pro-mask consensus was building for months before the WHO's advice formally changed in June to support face coverings. Strong evidence always trumps weak, but, in an extraordinary situation, weak evidence — especially when it converges from multiple disciplines — is arguably better than none. The final answer on airborne coronavirus transmission might well be blowing in the wind.

当前关于空气传播说法的不确定性呼应了国际社会对于口罩的争论。世卫组织(去年)6月才正式改变建议、支持佩戴口罩,在之前的数月中,各方一直紧张地建立支持佩戴口罩的共识。强有力的证据总是好过不充分的证据,但在特殊的情况下,不充分的证据——特别是当它横跨多个学科时——总比没有证据要好。关于新冠病毒究竟能否通过空气传播,目前我们很可能还无法得出一个最终定论。

0 条评论
评论不能为空