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In little noticed July interview, Fauci warned that widely used COVID tests may pick up 'dead' virus

Over-sensitive tests can pick up just "dead nucleotides" rather than live virus, he said.

Updated: December 10, 2020 - 10:41pm

​In recently resurfaced video from July, Dr. Anthony Fauci appeared to acknowledge that large numbers of positive COVID-19 cases may arise from oversensitive tests that pick up mere fragments of the virus rather than active, viable infections. 

If true, a sizable proportion of patients may have been unwittingly receiving positive test results that have little bearing on either their individual health or their risk of spreading the virus to others — suffering, in the process, much avoidable anxiety and disruption to everyday life.

At the same time, case numbers reported by public health authorities and major COVID tracking websites that conflate infection with infectivity and test-positivity with illness may leave the public with distorted impressions about both the virality and public health risks of COVID-19 to the general population. This may contribute in turn to popular overreaction and public health policy overreach.

Fauci's admission came on a July 16 episode of This Week in Virology, a longtime science podcast hosted by Columbia University virologist Vincent Racaniello. Fauci, the director of the National Institute of Allergy and Infectious Diseases, had joined the program to discuss various aspects of the COVID-19 pandemic, including testing. 

Concerns have been raised over the last several months that laboratory tests widely deployed to detect SARS-Cov-2 — what are known as polymerase chain reaction, or PCR, tests — may in fact be picking up remnants of the virus instead of clinically significant levels of infection. Some critics have argued that significant numbers of positive COVID-19 tests are actually not infectious at all.

At the center of the debate is the "cycle threshold" at which a PCR test operates. PCR tests work by multiplying a virus fragment over a series of cycles until it can reliably detect and confirm the virus within a sample. The more cycles a test must go through before it detects the virus, the smaller and weaker the original sample was.

High cycles, in other words, are expected to correlate to weaker viral samples, indicating that a positive case in that context may have a significantly different meaning in epidemiological or virological terms than would a lower cycle threshold positive. 

At high levels, 'the chances of it being [accurate] are minuscule,' Fauci says

Joining the hosts of This Week in Virology in July, Fauci directly responded to a question about COVID-19 testing, specifically how patients with positive tests might determine whether or not they are actually infectious and need to quarantine. 

"What is now sort of evolving into a bit of a standard," Fauci said, is that "if you get a cycle threshold of 35 or more ... the chances of it being replication-confident are minuscule." 

"It's very frustrating for the patients as well as for the physicians," he continued, when "somebody comes in, and they repeat their PCR, and it's like [a] 37 cycle threshold, but you almost never can culture virus from a 37 threshold cycle." 

"So, I think if somebody does come in with 37, 38, even 36, you got to say, you know, it's just dead nucleotides, period." 

Fauci noted that patients who receive a positive COVID-19 diagnosis are not immediately given the cycle threshold of their test. "When someone comes in and it's positive, they don't give them the threshold until you go back and ask for it," he said.

Fauci's office did not respond to requests for comment on his remarks in the July video. But his concession in that video stands as one of the most prominent admissions from a high-ranking federal official that widely used PCR tests may be giving a significantly skewed picture of the virus's current activity throughout the country. 

Vincent Racaniello, the Higgins Professor at Columbia University's Department of Microbiology & Immunology and the host of This Week in Virology, echoed Fauci's remarks when reached for comment on Sunday.

"I agree that in general, Ct values over 36 do not represent infectious virus, only pieces of viral RNA," he told Just the News. "Of course the Ct can also depend on the machine used and the primers so the number might vary depending on the lab."

"I recently had a PCR of Ct 34.7 which I considered negative," he said. "On retest in 3 days it was negative."

High-threshold tests appear to be widely in use in the United States. A review by the New York Times in August found that, of just one batch of positive tests from New York, Massachusetts and Nevada, "up to 90 percent of people testing positive carried barely any virus."

Individual test manufacturers and labs, rather than infectious disease authorities, are generally in charge of setting the cycle threshold of a COVID-19 test. "Most PCR assays for infectious diseases have Ct cutoffs in the range of 35-40," the Alaska Department of Health and Human Services states in a COVID-19 PCR informational document.

The state in that document noted that most of its PCR tests utilize cycle thresholds of 37, while its backup tests put the number as high as 40.

Positive COVID-19 tests have been greatly increasing since the beginning of October. On Thursday of this week the U.S posted a new one-day record of nearly 120,000 new cases, though — as has been the case for the course of the pandemic — it is unclear how many of those test results are indicative of illness and/or communicability  and how many are the product of the potentially misleading high cycle thresholds of the kind Fauci warned about.