Two months before the Super Bowl, the omicron surge decimated NFL rosters as players tested positive for covid-19. In mid-December, the NFL postponed a game between the Los Angeles Rams and Seattle Seahawks because the Super Bowl-winning Rams had 29 players out with covid.
The number of NFL employees testing positive per week in December rose from around 30 to around 300, most of them players who are expected to be absent from practices and games. The new variant “hit us like a ton of bricks,” said NFL Chief Medical Officer Dr. Allen Sills.
NFL Players Association medical director Dr Thom Mayer said the disruption highlighted a big question: If a player was vaccinated and recovered from covid but still tested positive, were there any conditions that might make it “reasonable to send them back [to the field] and safe to do so?
The NFL and the players’ association have determined that there are. The same week the NFL postponed the Rams-Seahawks game, the league made a small but significant change to its rules to allow players to return after testing positive for covid, a metric that relies on an obscure metric called the threshold. of cycle, or Ct value.
A Ct value indicates how difficult it was for the test to detect virus and therefore how much or how much virus was present in a person’s swab sample. Now players could go back either to the previous standard of two negative PCR tests, or with two PCR results that Mayer described as “slightly positive” – with a cycle threshold of 35 or more. They could also mix and match the two options.
The change essentially redefined what was considered negative to bring players back into the game earlier. In doing so, the NFL has entered a gray area of covid testing that has been debated by public health professionals throughout the pandemic: how to determine when someone is no longer contagious with covid.
The main problem is that there is no good way to know if a person is contagious. Antigen tests, the kind that people can do at home and record the results in minutes, are too “cold”, prone to passing away people who are in the early days of their infection. PCR tests are too ‘hot’, so sensitive that they can continue to register someone as positive after an infection clears.
But PCR tests often contain more information than just “positive” or “negative”: they can also indicate how many times the machine had to copy the genetic material of the virus into the sample before it produced enough. to actually see it. More cycles usually means the sample didn’t have much virus to work with; fewer cycles means there was enough virus in the sample to be easy to detect.
By setting a Ct value threshold for PCR testing, which some researchers argue, the NFL was essentially looking for middle ground by cooling the test too hot. Logic dictates that higher Ct values mean that less virus is present in the sample, so there is less chance that the person who provided it could infect another person.
“We’re looking for the sweet spot,” Sills said. “We don’t want to fire someone too soon who is contagious. We also don’t want to remove someone from an environment when they are not sick and no longer contagious.
Sills recently co-authored a Centers for Disease Control and Prevention article focused on NFL employees who tested positive for covid during the same week in mid-December. It showed that among 173 frequently tested and fully vaccinated NFL employees, about 70% were able to return to work before the end of the 10 days of isolation, under the new testing protocols.
The problem is that the use of Ct values to determine infectivity is not yet cleared by the FDA – PCR tests have received emergency use clearance for the sole purpose of determining if someone is ” positive” or “negative”, not to determine how positive it is. could be.
The CDC has stated that “an elevated Ct value can easily result from factors unrelated to the amount of virus in the sample” and that Ct values ”should not be used to determine an individual’s viral load, the degree of infection of a person, or when an individual can be released from isolation.
The NFL was ready to go because its employees were massively vaccinated, its covid cases were mostly mild, and internal data from previous variants suggested people with high Ct values weren’t able to spread the virus, Sills said. And, as Mayer pointed out, “if the games aren’t played, the players don’t get paid.”
Some researchers draw a line at a Ct value of 30, assuming that everyone with a test result below that number is likely infectious and everyone above probably isn’t. But other researchers were able to grow live virus from people with high Ct values, which is considered proof that these people were contagious. And over the past two years, laboratory medicine professionals have warned against using Ct values to make decisions about individual care, including determining who is infectious.
“It’s such a gray area right now, in terms of what exactly defines when you’re infectious and when you’re not,” said Dr. Stephen Master, president of the American Association for Clinical Chemistry, who released a statement on the summer saying Ct values shouldn’t be used and published a blog post in December titled “How to Say No to Reporting Ct Values”.
The Master said that a lot of work needs to be done to ensure that such results meet some kind of usable standard and that the fact that there is none is “an underestimated problem” even among best doctors. “Unless you have the gold standard and gold standard, it’s hard to know what’s real.”
Scientists working to develop a gold standard sent the same virus samples to more than 300 labs and found that what looked like a Ct value of 17 in one lab was a Ct value of 27 in another .
In concluding that no one whose test had a Ct value of 35 or higher could transmit the virus, the NFL Sills relied on data from the league’s 32 teams. And the NFL has circumvented a barrier to variability by requiring that all PCR tests be performed on the same lab equipment — Roche’s cobas analyzer — and by certain labs.
Even then, said Jim Huggett, a molecular biologist from the University of Surrey in the UK who has studied the variability of Ct values in labs around the world, two labs using the same equipment could get different results, which means that the same person on the same day could get different Ct values. blown before collection or the length of time the sample sat before being analyzed – both of which can affect Ct values.
Dr. Rosemary She, a pathologist at the University of Southern California’s Keck School of Medicine and director of microbiology at Keck Medical Center, said a high Ct value can sometimes amount to nothing more than a bad swab. .
In 2020, she co-wrote a letter while representing the College of American Pathologists that warned against using Ct values to determine what might be going on in a person’s body. Among the hospitalized patients she tests, a Ct value as high as 40 can mean either “the end of an infection” or just “poor sampling,” she said.
Dr. Robby Sikka, chair of the COVID Sports and Society task force — which advises tech companies, sports leagues and Broadway on their covid responses — is more optimistic about the usefulness of Ct values. He said data from sports and business circles are very promising. For example, his small preliminary study of 37 people in a highly vaccinated workplace showed that people who returned after at least five days of isolation, followed by two PCR tests with Ct values of 30 or more, did not transmit. not the virus to all colleagues.
At the community level, James Hay, an infectious disease epidemiologist at Harvard TH Chan School of Public Health, published a study in the journal Science that showed that only 30 positive PCR tests provide enough information, when Ct values are taken into account, to show whether an epidemic is growing or declining.
Researchers in South Africa and Great Britain are studying Ct values to track the direction of outbreaks, and Hong Kong scientists say Ct values provide a faster way to find out what’s going on than looking at case counts – and potentially faster than tracking the coronavirus in communities through wastewater samples.
KHN (Kaiser Health News) is a national newsroom that produces in-depth journalism on health issues. Along with policy analysis and polling, KHN is one of the three main operating programs of KFF(Kaiser Family Foundation). KFF is an endowed non-profit organization providing information on health issues to the nation.
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