NEW: All these months into the pandemic, we may have been testing the wrong way. Data from some state labs suggest up to 90% (!!) of people who get a positive result are no longer contagious and don’t need to isolate. Strap in, this is important. 1/x
Are we quarantining millions of people unnecessarily? Article by on pitfalls of #COVID19 PCR for quarantine / public heatlth action / policy. *Disclaimer* the article is based on my discussions with her. I want to clarify here: 1/17
Agree with that antigen tests have an important role, but disagree that high CT counts mean we shouldn’t contact trace. Tests are done at a single point in time - they don’t tell us anything about the history of infectiousness. 1/2
Stunning new research finds C19 PCR tests are much too sensitive to be useful in assessing spread. "In 3 sets of testing data...compiled by officials in MA, NY & NV, up to 90% of people testing positive carried barely any virus." The implications are huge.
Article by argues that we may be using too low a threshold for classifying PCR results as positive. Not mentioned is whetherhow this may change our assumptions of frequency of asymptomatic infections/transmission.
Massive thanks to who alerted me to this, and to and many others, incl at state labs. --/10
NYT finally acknowledging some facts, while 🇨🇦 media continues fear-mongering “Up to 90% of people testing #COVID19+ carried barely any virus” b/c PCR tests too sensitive & “detect.. genetic fragments—leftovers from infection that pose no particular risk”
Public service announcement from a #clinicalmicrobiologist - Ct is NOT a viral load... want set set positive at a threshold at <30 Cycles? Expect a lot of false negatives for seriously ill patients admitted to hospitals... 🤦‍♀️🤯
No idea how can cover so many aspects of the #SARSCoV2 #COVID19 #coronavirus pandemic. Here, she talked to me, , , , & about how too much testing sensitivity may not be a good thing.
As the NYT reported in an article you’ve probably read: “up to 90 percent of people testing positive carried barely any virus” Most correctly interpet this as evidence of the “Casedemic” being used to keep schools closed - because it is! 6
Up to 90 percent of people who test positive for the coronavirus are highly unlikely to spread it to others, according to data from two states. What should we do about that? 
Here is an article saying the #Covid19 Tests are too sensitive and showing too many False Positives
The NY Times is just realizing that a positive PCR test doesn’t necessarily mean a person is contagious. It’s estimated that only 10-30% of people who test positive actually have a high enough SARS-CoV-2 viral load to be infectious.
"Standard tests are diagnosing huge numbers of people who may be carrying relatively insignificant amounts of the virus. Most of these people are not likely to be contagious, and identifying them may contribute to bottlenecks..."
PCR positivity does not equal infectiousness. Rising “cases” don’t matter when ~90% of them can’t transmit and have mild or no symptoms. Protect the vulnerable and let everyone else get on with living.
"The standard [coronavirus] tests are diagnosing huge numbers of people who may be carrying relatively insignificant amounts of the virus. Most of these people are not likely to be contagious..." As many lockdown skeptics have said over the past six mos
Guter NYT Artikel, in dem Harvard Prof. M Mina Zukunft Coronatestung beschreibt. Er befürwortet genau wie ⁦⁩ die jetzt ignorierte Nutzung des ct Wertes bei PCR. Viele Positive sind so erkennbar nicht ansteckend, müssten nicht in Quarantäne
Up to 90 percent of people who test positive for the coronavirus are highly unlikely to spread it to others, according to data from two states. What should we do about that? 
The article by that quotes about finding too many positives in PCR tests is interesting. Both are superstars. But ppl are drawing conclusions that seem suspect. Thread. [1/
Up to 90 percent of people who test positive for the coronavirus are highly unlikely to spread it to others, according to data from two states. What should we do about that? 
Your Coronavirus Test Is Positive. Maybe It Shouldn’t Be. The usual diagnostic tests may simply be too sensitive and too slow to contain the spread of the virus.
This article and many other posts by point to a key challenge that has yet to be resolved: diagnosis for clinical purposes may not be the same as diagnosis for public health purposes.
Spot on ! From a COVID infectiousness point of view, maybe your qualitative (+/-) PCR is giving false pos, not that antigens are giving false neg. We need a Ct for PCR results!
“The standard tests are diagnosing huge numbers of people who may be carrying relatively insignificant amounts of the virus. Most of these people are not likely to be contagious.”
This issue that PCR positivity does not equal infectious positivity was also well reported in a recent article also by that has really raised awareness of why we MUST consider PCR Ct values. 5/
PCR Testing 101: "Each PCR cycle doubles the amount of targeted sequence (amplicon) in the reaction." 2 4 8 16 32 64 128 256 512 1024 2^30 = 1.1 BILLION "amplification" in EU. 2^40 = 1.1 TRILLION "amplification" in US. Even NYT has figured this out!
An important piece by with on the diff between *detection* & *viral load*. Unfortunately the headline is misleading & is being used to discredit PCR testing. (Search on Twitter). A PCR positive is a positive. No question.
Great article by in . Amazing that clinical folks still don’t get that viral load and potential dose of exposure to secondary contacts is important information. Shows widespread innumeracy that needs to be overcome.
85-90% w/ Covid-19 pos swab CT of 30-40 (=low viral load) in Massachusetts indicates: 1. V high % not infectious *when* diagnosed. 2. Most people getting tested way too late. Should use the 30-40 CT% as measure of testing strategy. ⁦
Reposting as promised. 90% of PCR Test producing positive results are not infectious. "False positives." False positive "cases" lead to false positive hospitalizations. False positive "cases" lead to false positive deaths. PCR tests are the problem.
This article is a frustrating framing of Covid19 testing. I agree that using viral load data is important, but it's an irresponsible way to pit public health activities against one another in US context of confused science comms & federal denialism/
via thanks ⁦⁩ for explaining that what we need isn’t fewer tests but different ones—tests that, counterintuitively, need to be LESS sensitive in order to pick up the cases that are truly infectious ⁦
Dr Mina is really on to something. Now that we’ve learned more about this virus, perhaps it’s time to focus on developing frequent, more available, point of care non-PCR based testing. ⁦⁩ ⁦⁩ ⁦
Up to 90 percent of people who test positive for the coronavirus are highly unlikely to spread it to others, according to data from two states. What should we do about that? 
This is a really fascinating article. Taught me something I didn’t know about virus testing and the lessons could have profound effects on policy interventions going forward.
wrote on the importance of ct value in this piece There still isn’t an agreed upon threshold value. “The CDCs own calculations suggest that it is extremely difficult to detect any live virus in a sample above a threshold of 33 cycle”
If the goal is to find infectious people, this is OK... or perhaps even better so that we are not isolating people who are no longer infectious. Again, covered in this article. (which admittedly caused some confusion) 7/
“The usual diagnostic tests may simply be too sensitive and too slow to contain the spread of the virus.” A great piece shedding some light on this by
The standard diagnostic test for the coronavirus may be too sensitive and too slow. This researcher has a better idea. 
I haven’t yet been tested for #COVID19 but I had thought results did show viral load/ amount of virus if +. It‘s a huge missed opportunity for further research if #PCR tests are only indicating positive or negative results.Are any #PCRs using CT of <35?
Are #coronavirus tests too sensitive? Should the standard for a positive test be revised to reflect whether or not there's enough virus to spread to others? Fascinating piece by
There’s a lot we don’t understand about #COVID19 but one thing is perfectly clear – #testing (more importantly #rapidtesting) is our best defense against the #virus.
The result of diagnostic PCR is not binary but a positive integer exponent for the number of steps required to amplify and detect a strand of genetic material. The more steps, the less viral load to begin with, assuming no errors. There is a large gray...
The usual diagnostic tests for #COVID-19 may simply be too sensitive and too slow to contain the spread of the virus
The challenge to our existing COVID testing paradigm continues with an excellent article in today's NYT.
Late to this but this ⁦⁩ story on the oversensitivity of PCR corona tests is really interesting and tells a complicated diagnostic thing quite deftly
Are the standard-issue coronavirus tests too good for our own good? on the science behind the tests and why ramping up use of antigen tests are key to curbing transmission via (Aug. 29)
Great article by who seems to have the pulse on covid19 reporting! This is also exactly why pooling with pcr is so great, pool size of 128 would correspond to a Ct shift of 7 cycles, and get rid of all these spurious false positives,...
"Your Coronavirus Test Is Positive. Maybe It Shouldn’t Be.' A rather excellent piece by which I wish I had written
But the testing is so sensitive that >90% of positive cases are neither contagious nor ill. That wasn't a big problem when we were testing only people we suspected of being ill; now that we're testing everybody, it's a huge problem.
Quote: “On Thursday, the United States recorded 45,604 new coronavirus cases ...If the rates of contagiousness in Mass. and N.Y were to apply nationwide, then perhaps only 4,500 of those people may actually need to isolate and submit to contact tracing.”
Current #SARSCoV2 tests are PCR and give a yes/no results. But they determine Ct data that correspond to viral load, which are ignored yet provide a window into a person's infectiousness
Your Coronavirus Test Is Positive. Maybe It Shouldn’t Be.
“I’m really shocked that it could be that high — the proportion of people with high C.T. value results. Boy, does it really change the way we need to be thinking about testing.”— I think calibrating #COVID19 cycle thresholds is definitely needed
Your #coronavirus Test Is Positive. Maybe It Shouldn’t Be: The usual diagnostic tests may simply be too sensitive and too slow to contain the spread of the virus. via
Your #Coronavirus Test Is Positive. Maybe It Shouldn’t Be. Up to 90 percent of people who test positive for the coronavirus are highly unlikely to spread it to others, according to new data, by via #Covid19 #TestTraceIsolate
This might make sense from a contact tracing perspective but failing to diagnose people who have a low viral load can have devastating consequences for their ability to get proper medical care & workplace accommodations. See:
Trump's positive was on a PCR test. Worth noting, as this Aug NYT piece does, that PCR tests are so sensitive that they often give positives when viral load is very low--i.e., less chance of serious illness and of further transmission.
more studies showing positive tests dont' mean infectious. We are using tests that have too high amplification (cycle times). hence positives tests don't mean panic. 90% were not infectious.
Your #Coronavirus Test Is #Positive and Maybe It Shouldn’t Be!!!!!
NYTimes raised questions about a PCR "positive." This video shows the PCR test isn't really a binary Y/N. Someone chose "40 cycles" threshold. Do we need a variable scale test? Are there discernable levels of infectiousness?
Your #Coronavirus Test Is Positive. Maybe It Shouldn’t Be “new data underscore the need for more widespread use of rapid tests, even if they are less sensitive.”
On Thursday, the United States recorded 45,604 new coronavirus cases. If the rates of contagiousness in Massachusetts and New York were to apply nationwide, then perhaps only 4,500 of those people may actually need to isolate and submit to contact tracing.
If your coronavirus test is positive. Maybe it shouldn’t be... #COVID19 #CoronaTesting #Medicine #DiagnosticTests #FDA