Hi,
Artikel im Science Magazin über Michael Mina, Epidemiologe der Harvard-Universität:
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AT THE MOMENT, THE UNITED STATES has no semblance of public-health testing” for the coronavirus, says Michael Mina, an assistant professor of epidemiology at both Harvard Medical School and the Harvard T.H. Chan School of Public Health. What does Mina—an expert in viral testing protocols—mean by that?
Zitat:
Current tests for active infection with SARS-CoV-2 are highly sensitive—but most are given to suspected COVID-19 patients long after the infected person has stopped transmitting the virus to others. That means the results are virtually useless for public-health efforts to contain the raging pandemic.
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Furthermore, such tests detect tiny fragments of viral RNA even after the patient has recovered. Mina says that means “the vast majority of PCR positive tests we currently collect in this country are actually finding people long after they have ceased to be infectious.” In that sense, a positive result can be misleading, because the results can’t be relied on to guide the epidemiological efforts of public-health officials, which are focused on preventing transmission and controlling outbreaks: “The astounding realization is that all we’re doing with all of this testing is clogging up the testing infrastructure,” with results arriving a week or more after tests are administered, “and essentially finding people for whom we can’t even act because they are done transmitting.” In fact the testing backlog is so dire, and so “absolutely horrendously useless as a system for public-health surveillance,” that Mina believes the United States should at the very least throw away the millions and millions of samples that are waiting to be tested—and perhaps even halt the current testing regime and just start over.
Zitat:
To do that, Mina says, everyone must be tested, every couple of days, with $1, paper-based, at-home tests that are as easy to distribute and use as a pregnancy test: wake up in the morning, add saliva or nasal mucous to a tube of chemicals, wait 15 minutes, then dip a paper strip in the tube, and read the results. Such tests are feasible—a tiny company called E25Bio, and another called Sherlock Biosciences (a start-up spun out of Harvard’s Wyss Institute for Biologically Inspired Engineering and the Broad Institute in 2019) can deliver such tests—but they have not made it to the marketplace because their sensitivity is being compared to that of PCR tests.
Mina says that is beside the point. “Imagine you are a fire department,” he says, “and you want to make sure that you catch all the fires that are burning so you can put them out. You don’t want a test that’s going to detect every time somebody lights a match in their house—that would be crazy: you’d be driving everywhere and having absolutely no effect. You want a test that can detect every time somebody is walking the streets with a flame-thrower.”
https://harvardmagazine.com/2020/08/...-public-health
Der zitierte Michael Mina auf Twitter, ich zitiere nur Teile daraus:
Zitat:
So much focus on sensitivity of the test. As though all tests must match up to PCR
But could focusing so much on achieving the greatest molecular sensitivity for asymptomatic testing *when testing is infrequent* be doing more harm than good?
I’ll explain
1/
Zitat:
The molecular tools we use like PCR for #COVID19 tests detect the virus genome.
Like detecting DNA in a piece of hair, detecting virus RNA tells little about whether the virus is still active...
2/
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But after the virus is cleared by the immune system, all of those viruses leave little trails of RNA behind. The RNA gets stuck in vesicles one the cells and it can sit there, in the nose or mouth, for weeks or months at very low levels...
4/
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The PCR test can continue picking up that leftover RNA the whole time it is there - for weeks or months AFTER the viral infection has been essentially cleared.
So ultimately, the majority of time spent in the PCR positive state is after infection, not transmissible
6/
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On the other hand, with a very sensitive test, people might stay positive for many weeks or even months bc it continues to detect the leftover RNA from the past infection.
But this can be bad - it leads to unnecessary quarantines of people already past their infection
9/
Zitat:
if doing low frequency screening of asymptomatics with PCR, the majority of people found to be positive will be detected only after their infection.
So in the US we are unnecessarily quarantining millions of ppl, assuming they are infected when they’re already recovered
10/
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And we are contact tracing all of these people and quarantining and testing their contacts looking only at the two days prior to their swab for the test - meanwhile they were likely infectious 1-5 weeks earlier! So wasting resources tracing the wrong people.
11/
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So maybe the most sensitive PCR test is not only costly for screening, but maybe even more damaging than a cheaper more frequent lower sensitivity test.
The apparent missed cases maybe aren’t false negatives. Maybe the (+) on the PCR are False (+) for actionable results
14/
Zitat:
To finish, high sensitivity PCR is great if youre a doctor and need to know what is wrong with your patient. Like a detective, you want all shreds of (RNA) evidence
But it’s not always better & sometimes a lower sensitivity test is more accurate at detecting active infection.
https://twitter.com/michaelmina_lab/...90611685404672
Zitat:
PCR positive for #COVID19 does not mean you are infectious
It means you have virus RNA
Like DNA left at a crime scene, it doesn’t mean the virus is still there
Virologists cautioned about equating PCR to live virus since the start of the “molecular revolution” in clinical labs
Anhang 46753
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To clarify the top tweet, it COULD mean you are infectious, but might not. A PCR with a very low Ct value means you are very likely infectious, should be isolated and contacts traced. Interpreting the Ct value is extremely helpful at the low Ct (high viral load) values to triage
https://twitter.com/michaelmina_lab/...90068897701888
Hier noch ein Welt-Artikel:
Zitat:
Wir müssen die Ergebnisse der PCR-Tests genauer auswerten
Ein positiver PCR-Test ist weder gleichbedeutend mit einer Corona-Erkrankung noch mit Infektiösität. Ein anderer Wert ist entscheidender. In Spanien reagiert die Politik auf diese Erkenntnisse – in Deutschland aber will die Debatte kaum einer führen.
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Seit Tagen wird über die Kopplung von Maßnahmen an Inzidenzwerte debattiert. Dabei liegt das Problem viel tiefer: bei den PCR-Tests selbst. Mehr als ein Jahr nach Beginn der Pandemie sollte sich die Öffentlichkeit darüber im Klaren sein, dass ein positiver PCR-Test weder gleichbedeutend sein muss mit einer Erkrankung noch mit Infektiösität. Um darüber Aufschluss zu bekommen, müsste nach der Testung eine Anamnese durchgeführt werden. Helfen würde es auch schon, den Ct-Wert des Testergebnisses in Augenschein zu nehmen – so, wie es im Ausland teilweise schon gemacht wird.
Zitat:
Ab einem Wert von etwa 30 ist eine Ansteckungsgefahr gemäß wissenschaftlichen Studien so gut wie ausgeschlossen. Angesichts der hohen Empfindlichkeit des PCR-Tests kann dieser schon beim Auftreten von minimalen Virusresten anschlagen, entweder zu Beginn einer Infektion oder eben auch während des Abklingens – und zwar bis viele Wochen danach und auch in Fällen, in denen eine Infektion nie bemerkt worden war. Entsprechend irreführend ist es, einen positiven PCR-Test als „Neuinfektion“ zu bezeichnen.
Zitat:
Der Harvard-Epidemiologe Michael Mina schrieb vor einigen Tagen bei Twitter: „Unglaublich, dass Ct-Werte zusammen mit einem positiven Sars-CoV-2-PCR immer noch selten gemeldet werden. Oft ist der Ct-Wert die einzige Information, die ein Arzt oder Kontaktnachverfolger über eine positive Person kennt. Dass wir Ct-Werte wegwerfen, ist bemerkenswert.“ In einem Interview mit dem „Science“-Magazin hatte er erklärt: „Wir müssen aufhören zu denken, dass jemand positiv oder negativ ist, sondern uns fragen, wie positiv jemand ist.“
Das letzte Zitat, in dem Quote,von ihm hat Potential für ein Meme!:biglaugh:
Zitat:
Unter anderem in der spanischen Hauptstadt Madrid hatten die Behörden nach eigenen Angaben Kontakt mit Mina und haben ihren Umgang mit PCR-Ergebnissen angepasst. Die Regionalregierung nimmt die Ct-Werte seit Monaten genau unter die Lupe und lässt sie mit in die Entscheidungen über die Verschärfung oder Lockerung von Maßnahmen einfließen; jüngst lag der Ct-Wert der positiven PCR-Tests in rund 50 Prozent der Fälle bei über 30.
https://www.welt.de/debatte/kommenta...auswerten.html
Gruß
Alef
