The NFL tweaked its testing procedures Friday for the novel coronavirus, mandating that a positive test under certain circumstances be confirmed by two more tests taken soon thereafter.

The modified protocol addresses a situation like that of Detroit Lions quarterback Matthew Stafford, who spent time on the team’s Covid-19 reserve list for what the Lions later called a false-positive test.

“We and others are clearly learning that not every single positive test means a new case of Covid infection,” Allen Sills, the NFL’s chief medical officer, said in a conference call with reporters.

Under the revised protocols, a positive coronavirus test by an asymptomatic individual with no known history of infection with the virus would be followed by two confirmatory tests taken on the day after the positive test result is received.

The player, coach or staff member involved would be kept isolated outside the team facility pending the results of the two follow-up tests. If both confirmatory tests are negative, the individual would be considered not infected by the virus and would be allowed to reenter the facility and rejoin team activities.

“We’ve always wanted to make sure that we provide the most accurate test results,” Sills said. “As I said, in doing 75,000 tests over the first two weeks, you collect a lot of learning. We’re constantly looking at all aspects of the protocol, how we can make it better. And we’re also constantly learning what these test results mean and how we can interpret them and how they match up with the clinical correlation.”

Sills said the NFL is trying to separate individuals with persistent positive tests (those who continue to test positive as long as months after recovering from an infection) and those with unconfirmed positive tests (those who have a single positive test within a string of negative testing results) from those whose positive test represents a new case of coronavirus infection.

The NFL Players Association announced Thursday that 56 players had tested positive between the opening of teams’ training camps July 21 and Wednesday. The league declined to confirm that number Friday, saying it continued to sort through the testing data to attempt to determine how many positive test results represent active new coronavirus infections.

When the Lions activated Stafford from the Covid-19 reserve list Tuesday, the team said in a written statement: “His testing sequence for the Pre-Entry period was: negative, negative, False-Positive. The next three tests were all negative. To be clear, Matthew does NOT have COVID-19 and never has had COVID-19 and the test in question was a False-Positive.”

NFL players, coaches and certain team staff members are being tested daily during the first two weeks of training camps. The protocols developed by the league and NFLPA say that the testing frequency can be reduced to every other day thereafter, based on the rate of positive tests. Sills said the NFL is open to the possibility of continuing daily testing, based on ongoing deliberations with the NFLPA. But he also stressed that mask-wearing, distancing measures and symptom screening are crucial safeguards.

“It’s very important that we understand that testing is not the foundation of our safety net for our clubs,” Sills said. “Testing is an important part of our overall system. But testing is one part of that system. And we continue to emphasize to everyone in our team ecosystem — players, coaches, staff, everyone — that testing alone is not what makes us safe.”

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