Scientists are debating whether to use a little-known measure to determine who is truly contagious. The NFL is already using it
Two months before the Super Bowl, the Omicron surge was decimating NFL rosters as players tested positive for COVID. In mid-December, the NFL postponed a game between the Los Angeles Rams and the Seattle Seahawks because the Rams, who would go on to win the Super Bowl, had 29 players out with COVID.
A Ct value indicates how hard it was for the test to detect the virus and therefore how much or how little of the virus was present in a person’s swab sample. Now, players could return either hewing to the previous standard of two negative PCR tests, or with two PCR results that Mayer described as “faintly positive”—with a cycle threshold of 35 or higher. They could also mix and match the two options.
In defining a Ct value cutoff for PCR tests, which some researchers support, the NFL was essentially seeking a medium ground by cooling off the too-hot test. The logic goes that higher Ct values means less virus is present in the sample, so there’s a smaller chance the person who provided it can infect another person.
The CDC has said “a high Ct value can easily result from factors not related to the amount of virus in the specimen” and that Ct values “should not be used to determine an individual’s viral load, how infectious an individual person may be, or when an individual person can be released from isolation.”
Master says it takes a lot of work to make sure that such results match some sort of usable standard and the fact one doesn’t exist is “an underrecognized problem” even among top doctors. “Unless you've got the reference method and the reference standard, it's hard to know what's real.”