A rash of COVID-19 results that forced multiple NFL teams to adjust their weekend training plans were false positives due to "isolated contamination during test preparation," the lab responsible said Monday.
NFL Network reported 77 individuals from 11 teams had initially tested positive on Saturday, but all had been cleared of having the virus.
"On August 22, BioReference Laboratories reported an elevated number of positive COVID-19 PCR test results for NFL players and personnel at multiple clubs," the lab's chairman Jon Cohen said in a statement.
"The NFL immediately took necessary actions to ensure the safety of the players and personnel. Our investigation indicated that these were most likely false positive results, caused by an isolated contamination during test preparation in the New Jersey laboratory."
The test results rattled a league gearing up for an on-schedule start to the season on September 10, with teams currently conducting training camps.
While leagues including the NBA and NHL resumed their coronavirus-disrupted seasons in controlled "bubble" environments to limit the spread of the virus, the NFL is planning for teams to play in their home stadiums, some with fans allowed depending on local restrictions as cases continue to climb in some parts of the United States.
When the positive tests were returned, the league said the teams involved immediately isolated the individuals involved and began contact tracing, in accordance with the protocols agreed by the league and players' union.
At the same time, the league noted Sunday that tests of NFL personnel conducted at other BioReference labs around the country had not returned similar results.
The Cleveland Browns had closed their headquarters and called of practice after the positive results on Saturday. Six Pittsburgh Steelers players were forced to miss training, as did players from the Buffalo Bills and Minnesota Vikings.