President Donald Trump announced in a late night tweet that he and first lady Melania Trump had tested positive for COVID-19, and as the story developed throughout the morning on Friday, others who have had contact with him in recent days have also announced positive test results.

Dr. Katherine Gergen Barnett told Boston Public Radio that anyone who has had contact with Trump or others with COVID should quarantine immediately.

"We know the height of contagion is usually when people show symptoms, but we also know that people can be contagious prior to showing symptoms," she said. "Anybody who's been in contact with President Trump, even if they are negative, at this point they need to be quarantined, the CDC recommends for 14 days."

It can take three days for exposure to the virus to show up as a positive test result, so even though Vice President Pence and his wife Karen announced they tested negative Friday morning, Gergen Barnett said they should quarantine.

"We're definitely not out of this window," she said.

Democratic presidential candidate Joe Biden, who debated Trump Tuesday night, tested negative Friday, he announced in a tweet.

According to the New York Times, Trump is experiencing mild, cold-like symptoms. The disease is most transmissable when patients are symptomatic, though there are documented cases of presymptomatic or asymptomatic transmission, and Gergen Barnett said it remains unclear how long Trump has been contagious.

She said the White House needs to be fully transparent about the status of the President and others.

"One of the most critical elements as American people we need, is to just have transparency about his medical condition," she said. "We don't know how serious his symptoms are, and we also know that COVID-19 can be mild initially, and then get quite severe."

UK Prime Minister Boris Johnson — who is in his mid-50s, and like Trump, overweight — became seriously illwith COVID-19 in March, and ultimately spent time in intensive care after self-isolating at 10 Downing St. with a fever for more than a week.

"I'm in no way presupposing that will happen in this case," said Gergen Barnett, "but it is absolutely something to be aware of, and again we just need transparency about how this is evolving."

Gergen Barnett is the Vice Chair of Primary Care Innovation and Transformation and the Program Director in the Department of Family Medicine at Boston Medical Center. She is also an assistant professor of Family Medicine at Boston University School of Medicine.