aOn Thursday, WELT posted a comment entitled “We need to evaluate the results of the PCR tests more accurately.” Four days earlier, author Christian Drosten, Charité’s chief virologist, asked via his employer how he felt about his 2014 PCR test statements. On a Friday afternoon, Charité sent responses from Drosten, which we document here in full.
I am looking at a PCR test This interview He met Professor Christian Drosten. Among other things, he says: “During the SARS outbreak in 2003, there was a strict definition of the condition. PCR was not tested on people who had been in contact with SARS patients but had no symptoms. Instead, they were subsequently tested. To look for antibodies to see if the infection has occurred. This should now happen also in Saudi Arabia. People who are asymptomatic should not be tested with PCR. “
I would like to know if Professor Drosten’s evaluation of testing people without symptoms differs in the Covid-19 pandemic, and if so, to what extent.
Answer from Christian Drosten:
The PCR test evaluation for Covid-19 and Mers varies widely, as both diseases have significantly different epidemiological characteristics.
At this point, only the following aspects should be mentioned: The SARS-CoV-2 virus (the pathogen of Covid-19) is transmitted very efficiently from person to person. About half of all transmissions occur before symptoms appear. It follows that the use of PCR to prevent transmission must also include people who have not (yet) shown symptoms.
On the other hand, Mers-CoV (the pathogen from Mers) and Sars-CoV (the pathogen from SARS) are only transmitted after symptoms appear. Therefore, testing people who show symptoms is sufficient here. Also, Mers-CoV is passively transferable from person to person. Most cases are obtained through direct contact with camels. Therefore, a large number of Mers cases must first be questioned – unlike Covid-19.
At the time of the interview I mentioned, I was in Saudi Arabia myself to investigate one of the largest volcanic eruptions in the city so far (Jeddah). At the time, it wasn’t entirely clear whether and how effectively the newly discovered virus could be transmitted from person to person. At the same time, many hospitals in the city were working with PCR tests that were not fully validated – because they were new.
The quality and reliability of the results obtained were uncertain. At the time, some local media outlets doubted that the outbreak was present, while others were highlighting the situation. In order to get a strong overview of the actual spread of the virus in hospitals, it suggested testing only patients who are showing symptoms of polymerase chain reaction (PCR). This greatly improves the likelihood of pre-testing and thus reduces the risk of false positive evidence with tests that have been verified with uncertainty. Additional antibody testing has also been suggested in order to increase the reliability of laboratory diagnostics.
The tests available at the time were in no way comparable to the Sars-CoV-2 tests available today. As mentioned in the interview I mentioned using the SARS (pathogen: SARS-CoV) example, the safe procedure (PCR test for symptomatic patients, confirmation by antibody test) is the method of choice if an agent is detected New nurse with unconfirmed tests. I must.
Sars and Mers were outwardly similar, because the PCR technique in many of the places where these pathogens occurred was not well developed yet. Certified PCR tests were not commercially available. Also at SARS, many regional laboratories lacked experience with PCR lab protocols. At the same time, the number of cases was relatively small, so antibody testing in addition to PCR may be recommended for safety.
This cannot be compared to the current situation with Covid-19. The release and transmission of the virus from SARS-CoV-2 has become apparent since the spring of 2020. PCR tests for Sars-CoV-2 are better validated and technically prepared from the start (this is simply due to technological advances) and are now available according to certified laboratory diagnostics Formally from a large number of manufacturers.
The tests vary, so not only one target gene is used, but a large number of target genes are used – with complete agreement of test results between manufacturers. Such a well-defined tool as other common viruses (hepatitis, influenza, HIV, and herpes viruses) was not present for Sars-CoV and Mers-CoV.
Of course, in the case of Sars-CoV-2, several antibody tests were performed at the initial stage to confirm the infection later (eg from Germany: Wölfel at al, Nature 2020 based on “Webasto cohort”). Post confirmation of infection in the case of PCR positives by means of a regularly successful antibody test so that mandatory confirmation from a laboratory medical point of view can be dispensed with.
Harvard professor Michael Mina, who is currently working extensively on his work, believes that a purely positive PCR test result is not sufficient to identify the infection, because people who survive the infection will remain positive for weeks that they can be tested. Mina advocates that the Ct value of each test be included in the evaluation of each case. How does Professor Drosten assess this debate, which in my opinion is more intense outside Germany?
Answer from Christian Drosten:
I made the same proposal in the summer of 2020 (see the “Time” articlePlan to fall5 August 2020). Together with RKI, I worked extensively on establishing the Ct or viral load standard. This has now been made available to all diagnostic laboratories, so that PCR results based on viral load or best are possible. Measurement of viral load is already used in many guidelines and in practice for the Public Health Service.