新冠病毒的“假陰性”是怎么回事？

You had some exposures that may put you at risk for coronavirus. A few days later you come down with a bad cough yourself and feel a little short of breath and really tired. You take your temperature: 101 degrees. A fever.

某些場合可能使你有感染冠狀病毒的風險。幾天后，你咳嗽得厲害，感覺有點喘不上氣，十分疲倦。你量了一下體溫：38度3。發(fā)燒了。

You suspect you might have Covid-19, the disease caused by the novel coronavirus. The days roll into each other, and your doctor urges you to stay home unless your condition worsens. You feel pretty bad, though, and finally get an appointment.

你懷疑你可能得了Covid-19——由新型冠狀病毒引起的疾病。日子一天天過去，你的醫(yī)生建議你待在家里，除非病情惡化。但你感覺很難受，最終還是預約去看醫(yī)生。

They test you for influenza by sticking a swab far up your nose, and you are told the test came back negative, you don’t have flu. They tell you they are saving the Covid-19 tests for those who are even worse off than you are. You go home with a prescription for antibiotics, possibly because they don’t know what else to do, and read about celebrities who are testing positive but don’t seem so sick.

醫(yī)生把拭子探進你鼻子深處，檢測你是否患了流感，你被告知結果是陰性，并沒有得流感。他們告訴你，Covid-19的檢測得留給那些情況比你更糟的人。你拿著抗生素處方回了家，可能是因為醫(yī)生也不知道還能給你開什么藥，你又看到一些名人檢測結果是陽性，但似乎病得沒那么嚴重。

A couple of days later, still with fevers, you go back, and the doctors relent and test you for SARS-CoV-2, the virus that causes Covid-19. They again stick something up your nose to what feels like the bottom of your eyeball.

幾天后，你還在發(fā)燒，又回到醫(yī)院，醫(yī)生們讓了步，給你做了SARS-CoV-2檢測，也就是引發(fā)Covid-19的病毒。他們又把什么東西塞進你的鼻子里，仿佛捅到了眼球底部。

They tell you that the results will be available in a couple of days and you go home and wait. Finally, the results come back and you are told you do not have Covid-19. Now what?

他們告訴你檢測結果要幾天后才出，你可以回家等待。最終，結果出來了，你被告知你并沒患上Covid-19。接下來該怎么辦呢?

This is a real patient’s story. In fact, it is a lot of people’s story — at least some version of it. Across the world, people with signs and symptoms of Covid-19 are testing negative and wondering what it means. They are not showing up in the statistics, and they are left in limbo about what to do next.

這是一則真實的病人故事。事實上，也是很多人的經(jīng)歷——至少某些部分是一樣的。在世界各地，很多出現(xiàn)了Covid-19體征和癥狀的人檢測結果呈陰性，他們想知道這意味著什么。這些人沒有出現(xiàn)在確診數(shù)據(jù)中，對下一步該做什么也束手無策。

The problem may be with the test. Current coronavirus tests may have a particularly high rate of missing infections. The good news is that the tests appear to be highly specific: If your test comes back positive, it is almost certain you have the infection.

問題或許出現(xiàn)在檢測上。目前的冠狀病毒檢測可能有特別高的漏檢率。好消息是，這種檢測似乎是高度明確的：如果你的檢測結果呈陽性，幾乎可以肯定你感染了病毒。

The most common test to detect the coronavirus involves a process known as reverse transcription polymerase chain reaction, or RT-PCR, a jumble of words that describes a method capable of detecting virus particles that are generally present in respiratory secretions during the beginning of an infection. From a technical standpoint, under ideal conditions, these tests can detect small amounts of viral RNA.

檢測冠狀病毒最常見的方法涉及一個稱為“逆轉錄聚合酶鏈式反應”(RT-PCR)的過程，這一長串字是一種檢測病毒顆粒的方法，這些顆粒通常出現(xiàn)在受感染初期的呼吸道分泌物中。從技術角度看，在理想條件下，這些檢測可以檢測出少量的病毒核糖核酸(RNA)。

In the real world, though, the experience can be quite different, and the virus can be missed. The best the Centers for Disease Control and Prevention can say is that if you test negative, “you probably were not infected at the time your specimen was collected.” The key word there is “probably.”

但在現(xiàn)實世界中，這一過程可能會大不相同，病毒可能會被漏掉。疾病控制和預防中心(Centers for Disease Control and Prevention)也只能說，如果你的檢測結果為陰性，“你可能在進行樣本采集的時候并沒被感染。”這里的關鍵字是“可能”。

False-negative test results — tests that indicate you are not infected, when you are — seem to be uncomfortably common. Increasingly, and disturbingly, I hear a growing number of anecdotal stories from my fellow doctors of patients testing negative for coronavirus and then testing positive — or people who are almost certainly infected who are testing negative.

假陰性的檢測結果——即你已經(jīng)被感染，但檢測表明你沒有——似乎是十分常見的現(xiàn)象。令人不安的是，我逐漸從我的同行醫(yī)生那里聽到越來越多的軼事，比如病人的冠狀病毒檢測呈陰性，然后又呈陽性;或是有些幾乎肯定被感染的人檢測結果呈陰性。

Unfortunately, we have very little public data on the false-negative rate for these tests in clinical practice. Research coming out of China indicates that the false-negative rate may be around 30 percent. Some of my colleagues, experts in laboratory medicine, express concerns the false-negative rate in this country could be even higher.

不幸的是，在臨床實踐中關于這些檢測假陰性率的公開數(shù)據(jù)非常少。來自中國的研究表明假陰性率可能在30%左右。我的一些檢驗醫(yī)學專家同事?lián)?，美國的假陰性率可能更高?/p>

There are many reasons a test would be falsely negative under real-life conditions. Perhaps the sampling is inadequate. A common technique requires the collection of nasal secretions far back in the nose — and then rotating the swab several times. That is not an easy procedure to perform or for patients to tolerate. Other possible causes of false negative results are related to laboratory techniques and the substances used in the tests.

在現(xiàn)實情況中，有很多原因會導致檢測呈假陰性。也許是取樣不充分。一種常見的方法是深入鼻子后部收集鼻分泌物，然后將拭子旋轉幾次。這不是個容易完成的步驟，病人也難以忍受。其他可能導致假陰性結果的原因，則與實驗技術和檢測使用的物質有關。

So, where does that leave us? Even with more testing, we are likely to be underestimating the spread of the virus. For now, we should assume that anyone could be carrying the virus. If you have had likely exposures and symptoms suggest Covid-19 infection, you probably have it — even if your test is negative. We should all continue to practice the behaviors — rigorous hand washing, not touching the face, social distancing — that impede its spread. And we need better information about the performance of these tests — including any new tests that are introduced — in the real world.

那么，我們還能怎么辦呢?即使進行更多檢測，我們也可能會低估病毒的傳播。眼下，我們應該假設任何人都可能攜帶病毒。如果你可能接觸過病毒，并顯出Coivd-19的癥狀，那么你可能已經(jīng)被感染——哪怕你的檢測結果是陰性。我們都應該堅持嚴格洗手、不摸臉、保持社交距離這些行為來阻止病毒的蔓延。我們還需要更好地了解這些檢測——包括所有新引入的檢測——在現(xiàn)實世界的表現(xiàn)。

Even as better tests emerge, we should always put the test result in the context of the other information we have. It’s a lesson that endures throughout medicine: Look at the big picture, not a single piece of data. Triangulate on the truth, using all the sources of information you have, no matter how good a single test. And don’t be shy about questioning a conclusion that doesn’t fully fit the facts.

即便出現(xiàn)了更好的檢測辦法，我們也要始終將檢測結果與掌握的其他信息聯(lián)系到一起。這是貫穿醫(yī)學始終的一課：從大局出發(fā)，而不只看單一的數(shù)據(jù)。不管某一次檢測結果有多好，也要利用你掌握的所有信息來源，對真相進行三角測算。面對與事實不完全相符的結論，要敢于去質疑。