空気感染しないというWHOの反論が下。米国のCDCはWHOの見解をそのまま転載しているようだ。空気感染の定義にもよるが、例えば咳により口から飛びだすドロップレットの飛距離は想像以上、１０メートルを超すとか昔に記憶している。その間空気中に浮いているということである。いずれにせよ、慎重に行動することに変わりはない。例えば人との距離を６フィートぐらいに置くというのが推薦基準としてアメリカの記事によく見かける。
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WHO Reviews 'Available' Evidence On Coronavirus Transmission Through Air
March 28, 2020 5:19 PM ET, Writer: Nell Greenfieldboyce
The World Health Organization says the virus that causes COVID-19 doesn't seem to linger in the air or be capable of spreading through the air over distances more than about three feet.
But at least one expert in virus transmission said it's way too soon to know that.
"I think the WHO is being irresponsible in giving out that information. This misinformation is dangerous," says Dr. Donald Milton, an infectious disease aerobiologist at the University of Maryland School of Public Health.
The WHO says that "according to current evidence," the virus is transmitted through "respiratory droplets and contact routes." By that, the agency means the virus is found in the kind of big droplets of mucus or saliva created through coughing and sneezing.
These droplets can only travel short distances through the air and either land on people or land on surfaces that people later touch. Stopping this kind of transmission is why public health officials urge people to wash hands frequently and not touch the face, because that could bring the virus into contact with the nose or mouth.
Other viruses, however, get shed by infected people in a way that lets the germs actually hang suspended in the air for minutes or even hours. Later, these airborne viruses can get breathed in when other people pass by. Measles is a good example of that kind of transmission—the Centers for Disease Control and Prevention says that "Measles virus can remain infectious in the air for up to two hours after an infected person leaves an area."
The WHO said that this kind of airborne transmission of the new coronavirus might be possible "in specific circumstances and settings in which procedures that generate aerosols are performed," such as when a patient is intubated in a hospital or being disconnected from a ventilator.
Based on that, the agency recommends "airborne precautions" when medical workers do those procedures. Otherwise, the WHO says, healthcare workers caring for COVID-19 patients could use less protective "droplet and contact precautions."
That troubles Milton, who says so little is known about this new virus, SARS-CoV-2, that it's inappropriate to draw conclusions about how it is transmitted.
"I don't think they know and I think they are talking out of their hats," Milton says.
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