Several cases have been confirmed among those who have had close contact with Donald Trump and his aide Hope Hicks, whose diagnosis prompted the test that confirmed the US president had the coronavirus.
The period between infection and sickness can be anything from a few days to two weeks, so he could have contracted it on a number of occasions and from a variety of people.
Here is a summary of some of those involved so far:
Donald Trump, 74
US president since 2016, he has seen his campaign effectively put on hold after testing positive for COVID-19.
He was at the White House Rose Garden last Saturday 26 September to announce the nomination of Judge Amy Coney Barrett to the Supreme Court. He attended a rally in Pennsylvania on Saturday night, and another event in Ohio on Monday.
On 26 September Donald Trump held an event in the Rose Garden to announce his nominee for the Supreme Court
He was at a fundraiser and rally on Wednesday in Minnesota, where he did a shorter speech than usual.
By Thursday morning Mr Trump would have been aware of the positive test result for Hope Hicks. Despite this, he went ahead with a fundraising trip to his golf club in New Jersey. According to public health guidelines he should have isolated, having been in close proximity to someone infected with the virus.
In the early hours of Friday, after returning from the New Jersey event, he tweeted to say he and his wife had tested positive and were in isolation.
Hope Hicks, 31
Presidential adviser and former White House communications director. She is a close confidante to Mr Trump.
Ms Hicks was not at the Rose Garden event on 26 September.
She was part of the team who travelled with Mr Trump to Cleveland for the presidential debate on Tuesday. She returned a negative test on Wednesday morning and joined others for the trip to Minnesota that day. It was in Minnesota that she reported feeling unwell.
She stayed apart from others on the first leg of the journey (by plane) and did not take the crowded Marine One back to the White House. On Thursday morning her test was positive. Those who had been near her were not immediately told.
Melania Trump, 50
First lady, wife of Donald Trump.
She often travels with her president husband and she was at the Rose Garden event in late September.
Her diagnosis was announced at the same time as her husband’s on Friday 2 October.
She tweeted later in the day that she was experiencing “mild symptoms” and was “overall feeling good”, adding: “I am looking forward to a speedy recovery.”
Kellyanne Conway, 53
Former presidential adviser who left the White House in August.
She was at the Rose Garden event on Saturday, sitting in the front row.
Pictures of the event showed a few hundred people sitting close to each other, many without masks, including Mrs Conway.
She tweeted: “My symptoms are mild (light cough) and I’m feeling fine.”
Senator Mike Lee, 49
Republican from Utah, Mr Lee was also at the Rose Garden last Saturday and met Amy Coney Barrett, who was announced as Mr Trump’s pick for the vacant seat on the US Supreme Court, a few days later.
He announced he had tested positive for COVID-19 on Friday, after a negative result earlier in the week.
Senator Thom Tillis, 60
Republican from North Carolina and a member of the Judiciary Committee.
He had a negative test before attending the White House Rose Garden event on Saturday and he met Mr Trump’s Supreme Court nominee Ms Coney Barrett on Wednesday. Mr Tillis was pictured wearing a mask at the Saturday event, but not at the Wednesday meeting.
On Thursday night he took part in a debate with the Democratic challenger for his senate seat, Cal Cunningham. Both wore masks.
Mr Tillis revealed his positive test result on Friday. Mr Cunningham has said he will get tested.
John Jenkins, 65
President of the University of Notre Dame, Mr Jenkins is another person who was at the Rose Garden event last Saturday and who announced his positive test result on Friday.
The university’s vice president Paul Browne said in a statement that Mr Jenkins had “learned that a colleague with whom he has been in regular contact tested positive for COVID-19”.
Bill Stepien, 42
The president’s campaign manager has also tested positive for the coronavirus and is experiencing “mild flu-like symptoms”.
Mr Trump’s immediate campaign events have all been cancelled, and his next debate with Democrat Joe Biden, scheduled for 15 October, is now in question.
The trio tested positive on Friday after spending last weekend at the White House or travelling with Mr Trump, according to Zeke Miller, president of the White House Correspondents’ Association.
Joe Biden, 77
Democratic presidential candidate, Mr Biden debated with Mr Trump in Cleveland on Tuesday.
Unlike Mr Trump, Mr Biden has regularly worn a mask when in public. However, during the exchanges, he was not wearing one.
Many people in the audience, including Mr Trump’s family members, were also not wearing masks.
Both Mr Biden and his wife Jill tested negative on Friday.
Kamala Harris, 55
Mr Biden’s running mate, candidate for vice president, had a routine test and the result was negative on Thursday.
Amy Coney Barrett, 48
Mr Trump’s nominee for the Supreme Court was at the Rose Garden event on 26 September to accept her Supreme Court nomination.
She recovered from a confirmed case of the coronavirus earlier this year.
Mike Pence, 61
The US vice president and his wife Karen tested negative on Friday morning.
According to reports, Mr Pence was in the Oval Office with the president on Tuesday and was last publicly seen with him at a Monday news conference.
William Barr, 70
The US Attorney General was at the Rose Garden event on 26 September and was seen without a mask, speaking with Mrs Conway, but he tested negative on Friday, a Department of Justice spokesperson said.