Wajngarten, who posted a picture to his Instagram account that shows him side-by-side with Trump, developed flu-like symptoms and tested positive for the virus that has become a global pandemic, the Brazilian presidency said in a statement.
Trump said he was unconcerned, and downplayed his contact with "the press aide," apparently referring to Wajngarten.
"I did hear something about that. We had dinner together in Florida, in Mar-a-Lago, with the entire delegation. I don't know if the press aide was there. If he was there, he was there. But we did nothing very unusual," he said.
"Let me put it this way, I'm not concerned."
Brazilian media reports said Bolsonaro had also been tested for the virus. Newspaper O Globo reported that the US embassy in Brasilia had contacted the Brazilian government for information on Wajngarten's test. The embassy did not immediately respond to a request for comment from AFP.
The Brazilian president's office "has taken and is taking all necessary preventive measures to protect the health of the president and all staff that traveled with him to the United States," it said in a statement.