The Brazilian embassy in Washington said on Friday that the country's charge d'affaires, Nestor Forster, tested positive after sitting at Mr Trump's dinner table. So, too, have a top aide to Brazilian President Jair Bolsonaro, who took a photo with Mr Trump and attended a party with him, and another person who attended a campaign fundraiser with the president that day, two Republican officials told AP.

Mr Trump, after days of insisting that he was not exhibiting symptoms of the virus, relented after being pressed by reporters about his resistance to testing when multiple lawmakers and countless citizens across the country who have had the same degree of exposure have not only tried to get tested, but also chosen to try to avoid potentially infecting others.

The president, according to AP, had been reluctant to take the test for fear it would project weakness or worry. Mr Trump has wanted to appear in full control during the crisis, and had expressed concerns that taking personal steps could undermine that appearance.

Mr Trump came into office as self-described germaphobe who tried to avoid handshakes as he conducted his real estate business. But he acknowledged on Saturday that he is now finding it difficult to resist shaking hands, a habit that he says he has picked up since becoming a full-time politician.

"People come up to me, they shake hands, they put their hand out," Mr Trump said. "It's sort of a natural reflex, and we're all getting out of it. All of us have that problem."

The White House is stepping up efforts to try to keep the virus at bay.

On Saturday, the White House announced that it is now conducting temperature checks on anyone who is in close contact with Mr Trump and Mike Pence, the vice-president, including reporters who attend a White House briefing and anyone entering the Oval Office.

Mr Pence also wrote a memo to White House staff on Saturday reminding them to take precautions such as avoiding physical contact, washing hands frequently and staying home when sick.