Thomas tested positive Wednesday after being in quarantine since Tuesday "out of an abundance of caution" following close contact with a person who later tested positive for the coronavirus, a statement said.
Thomas was among top military officers in quarantine who met with Ray at a secure conference room known as the "tank" at the Pentagon last Friday, Politico reported. Ray had attended the Pentagon meeting last Friday in place of Gen. David Berger, the Marine Commandant, who was traveling in Europe at the time.
Other senior officers who attended the meeting are also in quarantine and working from home as a precaution, including chairman of the Joint Chiefs of Staff, Army Gen. Mark Milley, and Gen. John Hyten, the vice chairman of the Joint Chiefs of Staff.
Other senior generals and admiral in charge of the Army, Navy, Air Force, National Guard, Space Force, and Gen. Paul Nakasone, who runs both the U.S. Cyber Command and the National Security Agency, have also been quarantining.
Pentagon spokesman Jonathan Hoffman said that all of the other senior leaders who came into contact with Ray have been tested for COVID-19 and, other than Thomas, no other tests came back positive.
Thomas "is experiencing mild symptoms, but otherwise is feeling well," a statement said.
Milley, Berger, Air Force chief of staff Charles "CQ" Brown and Army chief of staff Gen. James Conville attended a Sept. 27 event honoring Gold Star Families at the White House. The event took place one day after President Donald Trump held a Rose Garden ceremony announcing Judge Amy Coney Barrett's nomination to the Supreme Court to replace the late Justice Ruth Bader Ginsburg.
At least seven people who attended the Rose Garden ceremony have tested positive for COVID-19, including President Trump, first lady Melania Trump, University of Notre Dame President Rev. John Jenkins, White House counselor Kellyanne Conway, two Republican senators on the judiciary committee and a reporter.
Republic Sens. Mike Lee of Utah and Thom Tillis of North Carolina, who serve on the committee expected to hold hearing on Barrett's nomination on Oct. 12, are the two senators who tested COVID-19 positive.
Sen. Ron Johnson, R-Wis., also announced Saturday that he tested positive for the coronavirus after being exposed earlier in the week. though it's unclear where he contracted it, according to his office. Johnson is not on the judiciary committee, but his illness could impact his ability to be present when the Senate holds a full vote on Barrett's confirmation.
Trump's campaign manager, Bill Stepien, and former New Jersey Gov. Chris Christie, who helped Trump prepare for the first debate with Democratic presidential nominee Joe Biden have also tested positive for COVID-19, along with several other people linked to the White House.
Republican National Committee Chairwoman Ronna McDaniel, who was last seen with the president on Sept. 25, also tested positive for COVID-19 last week, and three White House have reporters tested positive.
The first COVID-19 case linked to the White House came last Thursday evening when Trump's senior advisor Hope Hicks was confirmed to have the virus. Since then, White House press secretary Kayleigh McEnany, and three of her press aides, including Jalen Drummond, Chad Gilmartin, and Karoline Leavitt, have tested positive for COVID-19.
On Tuesday, Stephen Miller, a White House senior advisor responsible for much of the administration's immigration policy, also tested COVID-19 positive and said he has since been in quarantine.
A White House email said Tuesday that "all contact tracing" for COVID-19 cases at the White House was complete.
The COVID-19 outbreak has infected "34 White House staffers and other contacts," in recent days, according to an internal government memo, ABC News reported.
The Marine Corps is following Centers for Disease Control guidelines, including quarantine and contact tracing, according to a statement.
"The Marine Corps remains operationally ready to answer the nation's call," the statement added. "Since April, the Marine Corps has been following, CDC and DoD [Department of Defense] guidelines for temperature testing, social distancing to the greatest extent possible, and the wearing of masks when social distancing is not possible."