The coronavirus pandemic for months has upended the daily work of Congress, which has seen a series of outbreaks.
Most recently, the Jan. 6 violent insurrection at the Capitol forced members to cluster together in rooms for several hours. Some House Republicans were seen not wearing masks during the ordeal, and refusing to do so.
And at least one holding room for House members included a lawmaker who was already positive, the Capitol attending physician told Congress.
"During this time, individuals may have been exposed to another occupant with coronavirus infection," said Dr. Brian Monahan, who urged members to seek testing.
Several members quarantined as a result of the concerns and at least one tested positive, including New Jersey Democratic Rep. Bonnie Watson Coleman.
This, as a wave of lawmakers have received the first shot of the Pfizer-BioNTech COVID-19 vaccine, which is now available to all members of Congress.
Senate Majority Leader Mitch McConnell, House Speaker Nancy Pelosi and top Senate Democrat Chuck Schumer were among the first to take part in the vaccinations.