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  It begins as surely as the leaves dropping off the trees.As the mercury drops and the sunlight fades,the sniffles set in.At best,it’s just a cold that leaves us with the strange feeling that we’ve swallowed a cheese grater;if we’re unlucky,our body is wracked with a high fever and aching limbs for up a week or longer.We have flu.


  The real reason germs spread in the winter


  The flu season arrives so predictably,and affects so many of us,that it’s hard to believe that scientists have had very little idea why cold weather helps germs to spread.Over the last five years,however,they have finally come up with an answer that might just offer a way to stem the tide of infection–and it revolves around a rather grim fact about the ways that your sneezes linger in the air.


  A new understanding of influenza couldn’t come quickly enough;worldwide,up to five million people catch the illness each flu season,and around a quarter of a million die from it.Part of its potency comes from the fact that the virus changes so quickly that the body is rarely prepared for the next season’s strain.“The antibodies we’ve built up no longer recognise the virus–so we lose our immunity,”says Jane Metz at the University of Bristol.It also makes it harder to develop effective vaccines,and although you can engineer a new jab for each strain,governments often fail to persuade enough people to take it up.

  人类的确应当尽早加深对流感的认识;每个流感季节,全世界都有多达500万人患病,其中约25万人会因此丧命。流感的破坏力之所以如此巨大,部分原因在于流感病毒的变异速度极快,往往令我们的身体对下一季的菌株措不及防。“我们体内的抗体已经无法识别这些病毒——所以我们失去了免疫力。”布里斯托大学的简·梅茨(Jane Metz)说。这也加大了开发疫苗的难度,虽然完全可以为每一种菌株都设计一种新的疫苗,但政府往往无法说服足够的人注射疫苗。

  The hope is that by understanding better why flu spreads in winter,but naturally fades in summer,doctors could find simple measures to stop its spread.Previous theories had centred on our behaviour.We spend more time indoors in the winter,meaning that we’re in closer contact with other people who may be carrying germs.We’re more likely to take public transport,for instance–and as we’re pressed against spluttering commuters,misting up the windows with their coughs and sneezes,it’s easy to see how this could send us over a tipping point that allows flu to spread through a population.


  Another popular idea concerned our physiology:the cold weather wears down your body’s defences against infection.In the short days of winter,without much sunlight,we may run low on Vitamin D,which helps power the body’s immune system,making us more vulnerable to infection.What’s more,when we breathe in cold air,the blood vessels in our nose may constrict to stop us losing heat.This may prevent white blood cells(the warriors that fight germs)from reaching our mucus membranes and killing any viruses that we inhale,allowing them to slip past our defences unnoticed.(It could be for this reason that we tend to catch a cold if we go outside with wet hair.)

  还有一个流行的观点则把分析重点集中于我们的生理机能:寒冷的天气会导致你的身体丧失对传染病的抵抗力。由于冬天日照时间缩短,我们体内的维生素D含量可能降低。由于维生素D有助于加强我们的免疫系统,因此这种营养物质的缺乏导致我们更容易患传染病。另外,在冷空气中呼吸时,鼻腔内的血管也有可能收缩,避免损失热量。这有可能阻碍白细胞(对抗病菌的斗士)到达鼻粘膜,使之无法杀死我们吸入的病毒,让病菌得以在不知不觉间绕过人体的防御系统。(或许正因如此,所以当我们湿着头发出门时很容易感冒。) 纽约时报中英文网 http://www.qqenglish.com

  While such factors will both play some role in transmission,analyses suggested that they couldn’t completely explain the yearly emergence of flu season.Instead,the answer may have been lying invisible in the air that we breathe.Thanks to the laws of thermodynamics,cold air can carry less water vapour before it reaches the“dew point”and falls as rain.So while the weather outside may seem wetter,the air itself is drier as it loses the moisture.And a steady stream of research over the past few years has shown that these dry conditions seem to offer the perfect environment for the flu virus to flourish.


  Lab experiments,for instance,have looked at the way flu spreads among groups of guinea pigs.In moister air,the epidemic struggles to build momentum,whereas in drier conditions it spreads like wildfire.And comparing 30 years’worth of climate records with health records,Jeffrey Shaman at Columbia University and colleagues found that flu epidemics almost always followed a drop in air humidity.

  例如,科学家已经通过实验研究了流感在豚鼠之间的传播途径。在潮湿的空气中,流感病毒难以积聚势头,而在干燥的空气中却会像野火般迅速蔓延。将最近30年的气候记录与健康档案进行对比后,哥伦比亚大学的杰弗里·沙曼(Jeffrey Shaman)和他的同事发现,流感爆发几乎总是伴随着空气湿度的下降。

  In fact,the overlap of the graphs was so close,“you could pretty much put one on top of each other,”says Metz,who together with Adam Finn,recently reviewed all the evidence for the Journal of Infection.The finding has now been replicated many times including analyses of the 2009 Swine flu pandemic.

  事实上,这两个图形的重叠度极高,“几乎可以用一个图形完全覆盖另一个。”梅茨最近与亚当·费恩(Adam Finn)共同为《传染病期刊》(Journal of Infection)评估了所有的证据。这一发现已经得到了反复的验证,包括2009年爆发的猪流感。

  That’s counter-intuitive–we normally think that the damp makes us ill,rather than protects us from disease.But to understand why,you need to grasp the peculiar dynamics of our coughs and sneezes.Any time we splutter with a cold,we expel a mist of particles from our nose and mouths.In moist air,these particles may remain relatively large,and drop to the floor.But in dry air,they break up into smaller pieces–eventually becoming so small that they can stay aloft for hours or days.(It’s a bit like the mist you get when you turn a hose pipe to its finest spray.)The result is that in winter,you are breathing a cocktail of dead cells,mucus and viruses from anyone and everyone who has visited the room recently.

纽约时报中英文网 http://www.qqenglish.com


  What’s more,water vapour in the air seems to be toxic to the virus itself.Perhaps by changing the acidity or salt concentration in the packet of mucus,moist air may deform the virus’s surface,meaning that it loses the weaponry that normally allows us to attack our cells.In contrast,viruses in drier air can float around and stay active for hours–until it is inhaled or ingested,and can lodge in the cells in your throat.


  There are some exceptions to the general rule.Although the air on aeroplanes is generally dry,it does not seem to increase the risk of catching influenza–perhaps because the air conditioning itself filters out any germs before they have a chance to circulate.And although the dry air seems to fuel the spread of flu in the temperate regions of Europe and North America,some contradictory results suggest the germs may act somewhat differently in more tropical areas.


  One explanation is that in particularly warm and wet conditions of a tropical climate,the virus may end up sticking to more surfaces within a room.So although it can’t survive in the air so well,the flu virus could instead be thriving on everything that you touch,making it more likely to pass from hand to mouth.


  But in the northern hemisphere at least,these findings could offer a simple way to kill the germs while they are still hanging in the air.Tyler Koep,then at the Mayo Clinic in Rochester,Minnesota,has estimated that simply running an air humidifier in a school for one hour could kill around 30%of the viruses flying around the air.Similar measures could(almost literally)pour cold water on other disease hotspots–such as hospital waiting rooms or public transport.“It would be a way of curbing the large outbreaks that occur every few years as the flu virus changes,”he says.“The potential impact in the cost of work days missed,schools days missed,and healthcare,would be substantial.”

  但至少在北半球,可以根据这些发现设计一种简单的方式,在病菌仍然漂浮在空气中的时候将其消灭。当泰勒·科普(Tyler Koep)就职于明尼苏达州罗切斯特市的梅约诊所时,他曾经估计,只要在学校里使用空气加湿器一个小时,就能杀死30%漂浮在空气中的流感病毒。还可以采取其他一些类似的措施,例如在医院大厅或公共交通工具等流感传播的热点地区泼洒冷水。“这可以抑制因为病毒的变异而每隔几年爆发一次的严重流感疫情。”他说,“疫情会导致企业停工、学校停课、健康受损,潜在影响十分巨大。”

  Shaman is now working on further trials,though he thinks that it will involve a tricky balancing act.“Though higher humidity is associated with lower survival rates for influenza,there are other pathogens,such as pathogenic mould,that thrive at higher humidity,”he says.“So care must be taken with humidification–it's not solely beneficial.”


  The scientists are keen to emphasise that measures like vaccines and good personal hygiene are still the best ways to protect yourself;using water vapour to kill the germs would just offer an additional line of attack.But when you are dealing with an enemy as mercurial and pervasive as the flu virus,you need to use every possible weapon in your arsenal.




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