新型ウイルスのスクリーニング「過半数を見逃し」、研究

【パリＡＦＰ＝時事】新型コロナウイルスの急速な感染拡大を阻止するために行われている世界的なスクリーニングの取り組みについて、失敗する可能性が高いと結論付けた研究論文が、科学誌「eLife」に発表された。航空旅客を対象としたスクリーニングは、どんなにうまくいったとしても、感染者の過半数を見逃すと警鐘を鳴らしている。（写真は資料写真）
　研究論文を発表した英米の研究チームは新型ウイルスへの主要な対抗策となっているサーモグラフィーや問診票を使ったスクリーニングの効果について、新型コロナウイルスの性質や潜伏期間に関する最新のデータに基づき、コンピューターモデルを使って予測した。
　研究チームは、２０１５年に発表された類似の研究を踏まえた上で、多数の感染者の見逃しは避けられないと結論付け、旅行者のスクリーニング方法を再考するよう各国に求めた。
　米シカゴ大学の博士研究員で論文の筆頭著者のケイトリン・ゴスティック氏はＡＦＰに対し、「平均すると、スクリーニングでは（新型コロナウイルスに）感染している旅行者の約３分の２が見逃されると推定される」と述べた。
　コンピューターモデルの予測によると、感染しているが発症していない「無症状」の患者が２０人に１人のみという最善のケースを想定した場合でさえ、５３％の感染者が見逃される。
　世界保健機関（ＷＨＯ）によると、新型コロナウイルスの潜伏期間は、通常で１０～１４日。つまり、感染者は知らず知らずのうちに他の人に感染させてしまう可能性があり、明らかな発熱を確認するための体温検査や、ウイルスへの暴露の自己申告はほぼ無意味だ。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2020/02/27-14:06）

Global screening efforts to prevent the rapid spread of coronavirus are likely to fail, according to new research warning that even best-case screenings of air travellers will miss more than half of infected people.
The novel coronavirus has infected more than 80,000 people worldwide since its emergence in central China last month.
Traveller screening using temperature monitors and questionnaires is a key response measure, yet the World Health Organization (WHO) on Wednesday said for the first time the number of new cases outside mainland China exceeded those within it.
Researchers in the United States and Britain in a study published in the journal eLife used computer models to predict the impact of screening, based on the latest data of how the coronavirus behaves and how long it takes for patients to show symptoms.
Building on similar work in 2015, they found that many cases would inevitably be missed and called for a re-think in how nations screen passengers.
If someone doesn't realise they have been exposed, and doesn't yet show symptoms, then they are fundamentally undetectable, Katelyn Gostic, a postdoctoral scholar at the University of Chicago and lead author told AFP.
We estimate that on average, screening will miss about two thirds of infected travellers.
Gostic stressed that these misses were not the result of human error, but rather an inevitable by-product of how the virus behaves.
The WHO says that the typical incubation period -- that is the time between a patient contracting the virus and symptoms showing -- is around 10-14 days.
This means that patients could be contagious without even knowing it, rendering temperature tests searching for a tell-tale fever and even self-reporting of exposure largely useless.
Upon screening, travellers fall into one of four categories: symptomatic but unaware of exposure; aware but asymptomatic; symptomatic and aware; and neither symptomatic nor aware.
Gostic and the team found that the final category were completely undetectable by traditional screening methods, and travellers in the third category could only be caught if they were willing to self report.
- 'Tipping point' -
Even assuming a best-case scenario where only one in 20 passengers were subclinical -- that is, infected but not showing symptoms -- the models predicted that 53 percent of cases would be missed.
Substantial fractions of the people who have tested positive in quarantine... did not show any detectable symptoms at the time of diagnosis, said Gostic.
Some of these people may be true subclinical cases. Others will probably develop symptoms in a few days time. Either way, these stories illustrate the difficulty of screening, where the goal is to detect cases as early as possible, but where people simply don't show detectable symptoms early in the course of infection.
Gostic warned that the world may be at a tipping point where screening and even the kind of quarantine measures seen in the outbreak's epicentre Wuhan are no longer effective.
Governments should be thinking about pandemic mitigation, she said.
But we should recognise the hard work and immense value that on-the-ground containment efforts have brought up until this point?providing time for healthcare workers and policy makers to prepare.