NEW YORK TIMES: UP TO 90% OF PEOPLE WITH “POSITIVE” COVID TEST RESULTS AREN’T INFECTIOUS
by Kevin Ryan
“Your Coronavirus Test Is Positive. Maybe It Shouldn’t Be.”
That’s the title of a New York Times article today that has very significant implications for COVID policy moving forward.
“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,” the New York Times writes.
“The tests being used are too sensitive, meaning they pick up even tiny fragments of virus that do not indicate a person is actually meaningfully infected.”
Indeed an investigation by the newspaper finds that up to 90% of positive test results are in people who are not infectious.
THE EXPLANATION
The PCR test searches for the virus by amplifying virus materials, essentially growing them in amplification “cycles” until they are detectable. The smaller the amount of virus, the more cycles are needed to detect it.
Often the test uses so many amplification cycles that even the tiniest genetic fragments – leftovers from infection that pose no risk whatsoever – trigger positive test results.
And the test result merely returns “Positive” or “Negative”, with no indication of how much virus was found, or how many amplification cycles were needed to find the virus (called the cycle threshold).
THE PROBLEM
A test result that simply says positive or negative “isn’t good enough” according the doctors interviewed for the New York Times article. It’s the AMOUNT of virus found that should dictate whether the test result should be categorized as positive, and what the patient should do next.
“It’s really irresponsible,” Dr. Michael Mina, an epidemiologist at the Harvard T.H. Chan School of Public Health. “We’ve been using one type of data for everything, and that is just plus or minus — that’s all. We’re using that for clinical diagnostics, for public health, for policy decision-making.”
“It’s just kind of mind-blowing to me… that they’re just returning a positive or a negative,” said Angela Rasmussen, a virologist at Columbia University in New York. “It would be useful information to know if somebody’s positive, whether they have a high viral load or a low viral load,” she added.
Just how many of the “positive” test results are from patients who have so little virus that they aren’t infectious?
The New York Times reviewed three sets of testing data from Massachusetts, New York, and Nevada. It found that 90% of people who tested “positive” carried barely any virus.
If that rate holds true for the entire county, it would mean that the United States has far fewer actual infectious cases of COVID than is being reported.
“On Thursday, the United States recorded 45,604 new coronavirus cases, according to a database maintained by The Times. 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,” the Times wrote.
Experts informed of these numbers were stunned.
“I’m shocked that people would think that [such small amounts of virus] could represent a positive,” Juliet Morrison, a virologist at the University of California, Riverside, said.
“I would say that none of those people should be contact-traced, not one,” Dr. Mina said.
The number of people with positive results who aren’t infectious is particularly concerning, said Scott Becker, executive director of the Association of Public Health Laboratories. “That worries me a lot.”
“I’m really shocked” Dr. Ashish Jha, director of the Harvard Global Health Institute, agreed. “Boy, does it really change the way we need to be thinking about testing.”
THE IMPLICATIONS
Just yesterday, California revamped its criteria for reopening businesses, basing it on how many positive test results a county has instead of hospitalizations, and setting the bar incredibly low. Just 1 new positive test per day out of 15,000 residents now keeps a county at the strictest level where nearly all businesses are shut down or heavily restricted.
But today’s revelation by the New York Times shows that such a move will essentially keep the state permanently locked down with little regard for how many of those positive test results are actually from infectious Californians, and how many are from overly sensitive PCR tests.
Indeed, most of the case-based measurements that the media has been using to gauge how the states are doing at controlling COVID may now be all but meaningless in light of the New York Times data.
Also, comparing the summer “surge” in some states to the spring outbreak is also now less meaningful. In the spring, only symptomatic people were being tested. Symptomatic people are those who have the highest viral loads, and therefore did not need a lot of “amplification” in their tests to result in a positive test.
But in the summer, the guidelines switched to testing more people, including those who were not symptomatic. This likely resulted in significantly more “positive” results from non-infectious patients.
THE SOLUTION
One solution would be to adjust the cycle threshold used to decide if a patient is infected. Most tests set the limit at 40. “Any test with a cycle threshold above 35 is too sensitive” scientists interviewed by the Times agreed. Dr. Mina said he would set the figure at 30, or even less.
From 70% to 90% of tests would no longer be judged positive if the amplification cycles were limited to 30, according to the Times.
And less sensitive, rapid tests should be used to verify positive PCR results, Dr. Mina said.
“In what may be a step in this direction, the Trump administration announced on Thursday that it would purchase 150 million rapid tests,” the New York Times article said.
SOURCES:
https://www.nytimes.com/2020/08/29/h...s-testing.html
https://covid19.ca.gov/safer-economy/
Originally Posted by Methais
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