Testing Accuracy for COVID-19 (CT Scan vs. RT-PCR), New California Cases (Lecture 27)
Welcome to another MedCram update. Let’s talk about California and testing. But before we do, let’s just review. Total confirmed 82,164; total deaths 2801; total recovered 32,897. We see more of a continuation of what we’ve been seeing in the past.
Let’s go to the Worldometer. We are going to talk a little bit about testing today and also the positivity rate. In UK, they have well over seven thousand tests, of which only 13 positive, and that’s a very low positivity rate of course. In Italy, where they actually have an outbreak, they’ve done over 9,000 tests, of which only 470 are positive; it’s about a 5% positivity rate. In France, 2.2 positivity rate; in Austria, 321 tests, of which two are positive. And then in the United States, notice, we have only done 445 concluded tests, of which 14 are positive, and that’s around 3.1 positivity rate.
These tests are not as sensitive as you may think. They could go to be surprised that the sensitivity on these tests are only around 70 percent, and so it is possible to have a negative test and to still be infected with the coronavirus.
We see that there are so far 334 new cases and one death in South Korea. And the number of confirmed cases is expected to jump in the coming days as health authorities have started testing more than 210,000 members of this church in Daegu.
If we look at the numbers coming out of China and the rest of the world in terms of total deaths, that seems to be leveling off, and if we look at the number of daily new cases outside of China, that has hit its highest amount ever on February 26th, with daily cases of 569.
I want to go to a local site, Eyewitness News, here in Southern California. A new case that has been detected in Northern California in a resident who has not traveled overseas. A couple of things that I want you to be aware of. This patient is a resident of Solano County; turns out that Solano county is the home to Travis Air Force Base where Americans returning from overseas were quarantined. The patient was transferred back on February 19, so that was about a week ago from undisclosed hospital to UC Davis Health, and that is the hospital in Sacramento for the University of California Davis. The patient had already been intubated, was on a ventilator, and was given droplet precaution orders because of undiagnosed and suspected viral conditions. So there are other viruses that can do this.
我想去南加州的一个本地站点，目击者新闻。在北加州的一个未曾出国旅行的居民中发现了一个新病例。我希望您注意几件事。该患者是索拉诺县的居民；原来，索拉诺县是特拉维斯空军基地的所在地，在那里，从海外归国的美国人被隔离。该患者于2月19日被转移回医院，大约是一周前从一家未公开的医院转移到UC Davis Health，那是位于加州大学戴维斯分校萨克拉曼多的医院。该患者已经被插管，正在呼吸机上，并且由于未诊断和怀疑的病毒状况而被给予了滴剂预防措施。因此，还有其他病毒可以做到这一点。
Now at the time, it seems as though UC Davis has asked the CDC for testing, but this was not done at the time. And if you go to the CDC website, it tells you what their requirements are for testing although they do put a disclaimer that they will look at a case-by-case basis. But essentially unless you travel to Wuhan or that part of China, they weren’t really going to be doing that kind of testing, so it’s unclear how eventually UC Davis was able to get the CDC to test this patient.
But they did, and eventually, on Sunday, the CDC ordered the covid-19 testing of the patient. At that time, the patient was put into airborne precautions. What does this mean? It means that anybody going into that room had to have an n-95 mask, and had to go into contact-isolation precautions. That means they would have to wear a gown, gloves. They may even have to wear eyewear protection. If they were not able to do that, then they would have to under something called peppers, where they basically go in with a mask that was vented.
From Sunday to Wednesday, it took for the CDC to confirm. Finally, the patient’s test was positive. The small number of employees were to go home and monitor their temperature for any kind of fever or things of that nature. And the key here is to recognize apparently this patient had NO travel to that part of the world.
They go on to say here at this time, the patient’s exposure is unknown. It’s possible that this could be an instance of what they call community-spread of covid-19, which would be the first time that this is happening in the United States. It’s also possible, however, they said that the patient may have been exposed to a returned traveler who was infected.
Of course, this brings up the issue of anybody that comes in with fever, or signs, and symptoms of a viral illness, and shortness of breath, could be potentially a carrier of this novel coronavirus. And that’s why it’s really important to have lots of personal protective equipment at hospitals where they belong instead of running out at hospital. So it’s really important that hospitals have the ability to acquire personal protective equipment because you don’t want to show up to a hospital where the employees there, or the doctors, or the nurses don’t have the adequate amount of protection so that they don’t pass the virus onto anybody else that might show up at that hospital. So please do not take masks and protective equipment from hospitals for your own use.
But this really brings up a big issue, and that is how do you test people for coronavirus? How do you know quickly whether or not this person that’s coming in has this virus? Obviously, if we see here in this case, it took them from Wednesday, when they actually got the positive test, all the way from Sunday, when they first ordered the tests. You can see that that’s not the optimal situation, especially when we add to the situation that this test is not really that sensitive, meaning that if you have a negative test, you can absolutely rule it out.
So enter a study that I think is going to be important, and that is this Science Daily News article, which talks about this article that was just published in Radiology called CT Provides the Best Diagnosis for COVID-19. I will put a link to it in the description below.
Basically what they did is in China, they looked at over a thousand patients, and they did this reverse-transcription-polymerase-chain-reaction, which is what RT-PCR stands for. This is where you look for the actual RNA of the patient and compared it to the classical findings that they see on CT scan.
Here’s another news item of the same article. So the title is CT Provides Best Diagnosis for COVID-19. And it says the study from China shows that chest CT demonstrates better sensitivity than this blood test looking for the actual PCR of the virus.
Remember that halfway through the epidemic last month, they changed the criteria, the definition, for the diagnosis of COVID-19. As you can see here in a study of more than a thousand patients that was published in the journal article Radiology, which I would link to so you can look at it for yourself, chest CT actually outperformed blood testing in the diagnosis of 2019 novel coronavirus, and this was looked at in Wuhan, China.
So it’s important to understand that you have to make an early diagnosis of COVID-19 if you’re going to isolate, and you’re going to prevent the spread of that disease. As we talked about earlier in an early JAMA article, 41 percent of patients who contracted COVID-19 did so in the hospital, and the majority of those, 41 percent, were healthcare workers.
According to the latest guidelines by the Chinese government, the diagnosis must be confirmed by reverse transcriptase-polymerase-chain-reaction, or the gene sequencing. They say here, however, that those throat samples are only about 30 to 60 percent positive at initial presentation. Having a low sensitivity implies that there’s going to be a lot of people who will be negative initially, and you’re going to miss those people. Those people are going to come through into your hospital and potentially infect other people, specifically people who are there to help and causing them to be taken out of work and put into isolation most likely.
And so they say here that early diagnosis of COVID-19 is crucial for the disease treatment and control. Compared to RT-PCR, that is the genetic testing, they say here that chest CT Imaging may be a more reliable, practical, and rapid method to diagnose and assess COVID-19, especially in the epidemic area.
So why did they think that? Well, let’s take a look and see the study. There were over a thousand patients who underwent both CT chest and RT-PCR tests from January 6 to February 6th, and what they did was they looked at all of those people who had a positive PCR, and there was about 601 of those. And everybody that had a positive CT scan, and there were 888 of those.
And then they asked the question. What’s the sensitivity? What’s the specificity? And what’s the accuracy? And what they found was that about eighty-one percent of patients with a negative RT-PCR but a positive CT scan were reclassified as highly likely or probable cases with COVID-19 based on the comprehensive analysis of clinical symptoms, typical CT manifestations, and dynamic CT follow-ups. What they mean by that? It was getting worse and they were consistent. They also found in a lot of these that the initial test may have been negative, but that follow-up tests turned positive, confirming in a lot of these cases the original CT findings.
Let’s review those results. The results showed that 59 percent of these patients that they tested had PCR results that were positive, 88% had positive CT scans. They said that the sensitivity, and this is something that you want to be very very high in this situation, because something that is very sensitive, it means that if it is negative, you can practically rule it out, and as it turned out that sensitivity of chest CT was 97 percent based on positive RT-PCR results.
In patients with negative RT-PCR results, 75 percent of those patients had positive CT findings, and of those 48 percent were highly likely cases. So what we’re seeing here is that CT scans may be the way to get a quick screening of whether or not your patient with fever is likely to have COVID-19. But the question is what are the findings on CT? It’s good enough to know that you should get a CT, but what is it that you should be looking for?
I’m going to link in the description below a YouTube video describes the findings on CT scan of known cases of covid-19, and that concludes our update for today. Realize that many of these videos are made the evening before they get released because I am still working in the Intensive Care Unit, seeing patients every single day. And so this is something that I do at the end of the day because we, as healthcare providers, run on the frontline, and we have to be prepared. Thanks for joining us.