Covid-19 is spreading further among those around US President Donald Trump, with White House adviser Stephen Miller and a top military official infected.
Mr Miller, who has been self-isolating for the past five days, confirmed on Tuesday that he had tested positive.
Several military leaders are also quarantining after Coast Guard official Admiral Charles Ray tested positive.
Meanwhile, Democratic candidate Joe Biden has said Mr Trump should not debate him if he is still infected.
Speaking about their scheduled second encounter in Miami, Florida, on 15 October, he said he would be guided by medical experts.
"I think if he still has Covid, we shouldn't have a debate," he said.
Mr Trump returned to work in the White House from hospital on Monday despite being diagnosed with the disease only last week.
While at Walter Reed Medical Center, he was treated with dexamethasone - a steroid medication usually given to severe and critical Covid-19 patients - and supplemental oxygen.
What do we know about Miller?
The Trump adviser said he was in self-isolation after "testing negative every day" until Tuesday.
He had been closely involved with the president before the latter fell ill, attending a meeting on 27 September to prepare for the first presidential debate in Cleveland, Ohio, and later taking flights with him on Air Force One, the New York Times reports.
His wife, Katie Miller, who is Vice-President Mike Pence's spokeswoman, contracted the virus back in May and later recovered.
In July, Mr Miller's 97-year-old grandmother, Ruth Glosser, reportedly died due to complications with Covid-19.
The White House denied that coronavirus had caused Mrs Glosser's death, saying in a statement she had "died peacefully in her sleep from old age".
But Mr Miller's uncle produced a death certificate listing "respiratory arrest" and Covid-19 as "a condition leading" to the cause of Mrs Glosser's death.
Mr Miller - who writes the president's speeches - is known for his hardline views on immigration.
What's the latest on the US military leaders?
Adm Ray, vice-commandant of the US Coast Guard, is said to be experiencing mild symptoms.
While officials who attended meetings with Adm Ray last week are now quarantining, none have so far tested positive or exhibited symptoms, the Pentagon said.
It is not known how Adm Ray contracted the virus. The admiral attended an event at the White House about 10 days ago but it is not clear if he contracted the virus there or elsewhere, officials told the Associated Press news agency.
Other White House officials have tested positive for coronavirus in recent days.
The Coast Guard said Adm Ray had tested positive on Monday and was isolating at home. It added that any Coast Guard personnel who had been in close contact with him would also quarantine.
Nearly all members of the Joint Chiefs of Staff - a body consisting of senior military officials who advise the US president - are in quarantine after attending meetings with Adm Ray last week, the BBC's US partner CBS News reports.
In addition to the chairman of the Joint Chiefs, General Mark Milley, those in quarantine are said to include the vice-chief of staff, army chief of staff, chief of naval operations, air force chief of staff, CyberCom commander, Space Force chief, chief of the National Guard and deputy commandant of the Marine Corps.
Pentagon spokesman Jonathan Hoffman told reporters there had been "no change to the operational readiness or mission capability of the US Armed Forces".
"Senior military leaders are able to remain fully mission capable and perform their duties from an alternative work location," he said.
The Pentagon is conducting contact-tracing related to last week's meetings.
Will the Florida debate go ahead?
Mr Trump has said he intends to take part despite fears that he will still pose a risk of infection so soon after falling ill.
Asked about the debate, Mr Biden said: "I think we're going to have to follow very strict guidelines. Too many people have been infected and it's a very serious problem. And so I'll be guided by the guidelines of the Cleveland Clinic and what the docs say is the right thing to do, if and when he shows up for debate."
Trump campaign spokesman Tim Murtaugh responded by insisting the president would "be healthy and will be there". "There's no getting out of this one for Biden, and his protectors in the media can't cover for him," he added.
One possible option would be for the two candidates to debate with each other virtually.
Meanwhile, plexiglass will be used to separate Mr Pence and Democratic vice-presidential candidate Kamala Harris and limit the risk of Covid transmission when they debate in Salt Lake city, Utah, on Wednesday. Both candidates recently tested negative.
An unnamed senior official close to Mr Pence told CBS News he did not want a plexiglass divider on his side of the stage but did not object to Ms Harris and moderator Susan Page having dividers if they wanted them.
Cases rising at the White House
First Lady Melania Trump, aide Hope Hicks and a number of Republican senators have all been confirmed as having the virus.
Press Secretary Kayleigh McEnany has tested positive, announcing her diagnosis on Monday, and three other members of staff in the press office - Chad Gilmartin, Karoline Leavitt and Jalen Drummond - have also tested positive.
Ms McEnany was seen speaking to journalists without wearing a mask on Sunday but said no members of the press had been listed as close contacts by the White House medical unit.
Many of the people in Mr Trump's inner circle who have tested positive attended a gathering at the White House Rose Garden on 26 September that is being scrutinised as a possible "super-spreader event".
Another coronavirus case to emerge from that event, at which the president unveiled his nominee for the US Supreme Court, is a Christian minister from California.
Pastor Greg Laurie, who is said to have mild symptoms, was also with Mike Pence earlier that day at a prayer march in central Washington DC.