A growing number of White House staff and senior Republicans have tested positive for Covid-19 since US President Donald Trump revealed last week that he had contracted the respiratory disease.
The infections have interrupted campaigning for the presidential election on 3 November, rattled financial markets and slowed the work of Congress, with the Senate vowing to delay any votes now that three members of the Republican majority have tested positive.
Several people who met Mr Trump last week said they had since tested negative, but it can take days for someone who has been exposed to the virus to develop symptoms or to test positive.