米、国民にマスク着用を推奨　トランプ氏発表　新知見で方針転換

【ワシントンＡＦＰ＝時事】ドナルド・トランプ米大統領は3日、新型コロナウイルス流行の拡大防止に向けた米政府の新たな方針として、国民に対し外出時のマスク着用を推奨すると発表した。（写真は資料写真）
　トランプ氏はホワイトハウスで開いた記者会見で、米疾病対策センターが人々に対し何らかの方法で顔を覆うよう要請していると説明。ただ、医療用マスクについては医療従事者が利用できるように入手を控えるよう促した。
　トランプ氏は、着用は「任意だ」と強調。「する必要はないし、私はしないことにした。ただ、一部の人々がしたいなら、問題ない」と述べた。記者会見の出席者にマスクをしていた人は一人もいなかった。
　従来は、患者とその世話をする人のみがマスクをすべきだとされていた。しかし最近になって、それ以外の人もマスクをすべきことを示す科学的根拠が出てきたと複数の米保健当局高官がマスコミに語っていた。
　米国立アレルギー感染症研究所のアンソニー・ファウチ所長は３日、ＦＯＸニュースに対し、マスク着用のガイドラインを変更する理由として、「新型ウイルスはせきやくしゃみだけでなく、会話をしただけでも伝染するという最新の情報がある」と語った。
　その数日前には米疾病対策センターのロバート・レッドフィールド局長が、感染者の最大４分の１が無症状の可能性があると述べていた。

■マスクで飛沫減少、一方で防護具が汚染源になる恐れも
　米科学アカデミーは１日、この問題に関する最近の研究結果をまとめた書簡をホワイトハウスに送付。その中で、最終的な結論はまだ出ていないものの、「現在入手可能な研究結果は、通常呼吸によるウイルスのエーロゾル（エアロゾル）化と整合性がある」と説明した。
　米保健当局はこれまで、新型コロナウイルスの主な感染経路は感染者のくしゃみやせきにより出る直径１ミリ程度の飛沫（ひまつ）だとしていた。この飛沫は直ちに約１メートル先へと落下する。だが、感染者が息を吐いた際にウイルスが超微細な霧状の粒子「エーロゾル」となって浮遊することが可能であれば、ウイルスの拡散阻止がより困難となり、顔を覆う必要性を裏付けることとなる。
　米科学アカデミーは香港と中国で行われた２つの研究に言及。香港の研究によると、マスクを着けた新型コロナウイルス感染症患者からの飛沫やエーロゾルはマスクを着けていない患者より少なかったという。
　一方、中国の研究によると、武漢の複数の病院を調べた結果、患者用トイレと医療スタッフが防護具を脱ぐ部屋でウイルスのエーロゾル化が顕著だったとしている。防護具を脱いだ際に微粒子が空中に舞い上がった可能性があり、医療従事者が使う防護具が汚染源になる恐れが浮上した。米科学アカデミーの専門家らは、これらの微粒子は呼吸で体内に取り込まれる大きさではないが、手などに付着する恐れがあるとしている。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2020/04/06-13:24）

President Donald Trump on Friday recommended that Americans cover their faces with masks when outdoors, a policy U-turn following growing scientific research suggesting their widespread use can stem the spread of the coronavirus.
Trump told a White House briefing that the Centers for Disease Control and Prevention (CDC) was urging people to wear face coverings like scarves or homemade cloth masks, but to keep medical-grade masks available for health workers.
It's going to be really a voluntary thing, he underlined. You don't have to do it and I'm choosing not to do it, but some people may want to do it and that's okay.
The about-face was widely expected after senior health officials told reporters the scientific evidence had evolved.
Speaking to Fox News on Friday, Anthony Fauci, head of infectious diseases at the National Institutes of Health, cited recent information that the virus can actually be spread even when people just speak as opposed to coughing and sneezing.
Days earlier, the CDC's Robert Redfield said up to a quarter of people who are infected may be asymptomatic.
Taken together, the developments represent powerful arguments in favor of the widespread use of facial coverings.
Previously, the advice was that masks should only be used by sick people and their caregivers.
The new recommendations are in line with those made by France's National Academy of Medicine on Friday, and by New York Mayor Bill de Blasio a day earlier.
The city has seen almost 1,000 of the US's nearly 7,000 deaths.
But the message was undermined by the fact that none of the officials present at Friday's briefing were following it.
Trump said he would not be wearing one as I greet presidents, prime ministers, dictators, kings, queens, I don't know, it somehow, I don't see it for myself.
- Breathing and speaking -
Fauci's comments about the virus's spread via breathing came after the National Academy of Sciences (NAS) sent a letter to the White House on April 1 summarizing recent research on the subject.
It said that though research isn't yet conclusive, the results of available studies are consistent with aerosolization of virus from normal breathing.
Until now, US health agencies have said the primary pathway of transmission is respiratory droplets, about one millimeter in diameter, expelled by sick people when they sneeze or cough.
These quickly fall to the ground around a meter (three feet) away.
But if the virus can be suspended in the ultrafine mist people expel when exhaling -- in other words, an aerosol -- it becomes much harder to prevent its spread.
- The aerosol debate -
A recent NIH-funded study published in the New England Journal of Medicine found that the SARS-CoV-2 virus could become an aerosol and remain airborne for up to three hours.
The paper received widespread attention even as critics said the findings were overblown because researchers had used a medical device called a nebulizer to deliberately create a viral mist, something they argued would not occur naturally.
The NAS letter pointed to preliminary research by the University of Nebraska Medical Center that found the genetic code of the SARS-CoV-2 virus, its RNA, in hard-to-reach areas of patients' isolation rooms.
The NAS scientists also cited two other studies -- both not yet peer reviewed -- from Hong Kong and mainland China.
The Hong Kong researchers had some patients with coronavirus and other viral respiratory illnesses wear masks, while other patients in the study didn't cover their faces.
They found fewer droplets and aerosols from coronavirus patients who wore masks.
The Chinese paper raised concerns that personal protective gear used by health workers could be a source of airborne virus.
The team studied hospitals in Wuhan and found two major areas where the virus was aerosolized: patient bathrooms and rooms where medical staff removed protective gear.
This may be because doffing protective gear causes particles to get re-suspended in the air. Even if these particles are not of breathable size, they could settle on people's hands and bodies, the NAS panel said.
So far, the World Health Organization has been more cautious on the airborne threat.
In an analysis published on March 29, it wrote that aerosol transmission was only known to occur during particular medical treatments that required assisted breathing.