We Still Don't Know When President Trump Last Tested Negative for COVID-19. Here's Why That's a Big Deal

It’s been only about four days since the world learned U.S. President Donald Trump tested positive for COVID-19—but that doesn’t necessarily mean it’s been four days since he was infected.

White House officials and Trump’s personal physician Sean Conley have repeatedly dodged questions about when the President last tested negative for COVID-19. “I don’t want to go backwards,” Conley said when asked about Trump’s last negative test during a Monday press briefing, at which he announced Trump would be discharged from Walter Reed National Military Medical Center to return to the White House.

But the question isn’t only important retroactively. “It matters for a couple of reasons,” says Dr. Megan Ranney, a professor of emergency medicine at Brown University. “The first is because it helps to predict the course of illness. The second reason it matters immensely is because of contact tracing.”