All of NFL's positive coronavirus tests from the weekend return negative

The NFL has cleared all individuals who tested positive over the weekend for the coronavirus, after what its testing partner called an "isolated contamination during test preparation." All of the original test results have been classified as false positives.

Eleven teams were affected by the mistake, with sources telling ESPN that 77 individuals had positive tests, leading to some anxious moments and altered Sunday practice schedules -- but ultimately no evidence of an outbreak. Buffalo Bills quarterback Josh Allen was among those whose initial test resulted in a false positive, forcing him to miss the team's Sunday practice, according to ESPN's Adam Schefter.

According to the sources, the NFL retested the original 77 samples, all of which had been processed at the same BioReference lab in New Jersey. All of the retests came back negative. The league also conducted quicker, point-of-care tests Sunday, and all of those tests also were negative.

According to training camp protocol agreed upon by the NFL and the NFL Players Association, the 77 individuals -- players, coaches and some staff members -- can resume their normal activities Monday.

BioReference, which the NFL hired to conduct all of its COVID-19 testing, uses five labs around the country to process the league's daily tests. The New Jersey lab was the only one to produce false positives over the weekend.

In a statement Monday morning, BioReference said: "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 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. Reagents, analyzers and staff were all ruled out as possible causes and subsequent testing has indicated that the issue has been resolved. All individuals impacted have been confirmed negative and informed."

In an email sent Sunday night to its members, the NFLPA said it has "initiated an investigation into both the testing process at the lab site in question and whether or not all of our protocols were followed."

Three of the hardest-hit teams over the weekend were the Minnesota Vikings, who had 12 individuals produce false positive tests, the New York Jets (10) and the Chicago Bears (nine). Those numbers created immediate alarms after the NFL had produced a low infection rate during the first month of training camp. As of Monday morning, only three players remained on the COVID-19 list.

Cleveland Browns coach Kevin Stefanski said he was among the false positives. A dozen of his players were cleared just ahead of Monday's practice. Stefanski wasn't able to lead Sunday's practice and stayed away from the team's practice facility as he waited to be cleared. Defensive coordinator Joe Woods led the practice instead.

"It's something I take seriously," said Stefanski, who initially found out about the false positive test early Sunday morning, "and our whole goal is to keep everybody safe."

The episode is likely to influence discussions between the NFL and NFLPA, who are working to finalize regular-season testing protocols. The sides must decide whether to continue daily testing, which expires Sept. 5, and create a policy for weeding out false positives when determining eligibility for games.

During training camp, all positive test results are followed by two additional tests over a 24-hour period. If both of those tests come back negative, the original test is classified as a false positive.

Information from ESPN's Jake Trotter was used in this report.