Tomoka Correctional Institution in Daytona Beach, Florida. Photo: Paul Hennessy/NurPhoto via Getty Images

96% of 3,277 inmates in state prison systems in Arkansas, North Carolina, Ohio and Virginia who tested positive for the coronavirus did not show symptoms, Reuters reports.

Why it matters: The findings suggest that asymptomatic patients could be contributing to the spread of the virus at a far higher level than suspected, especially in prisons, which have proven to be a breeding ground for COVID-19 in the U.S.

  • This is especially noteworthy because health officials have prioritized testing and surveillance for people that show symptoms. 4,693 total tests were conducted.
  • “It adds to the understanding that we have a severe undercount of cases in the U.S.,” Leana Wen, adjunct associate professor of emergency medicine at George Washington University, told Reuters.

The big picture: Two prisons — Marion Correctional Institute in Ohio and Chicago's Cook County jail — are among the largest known sources of coronavirus infections in the U.S.

  • At Marion, close to 95% of the 2,028 inmates who tested positive for the virus were asymptomatic, according to Reuters.

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Updated 13 hours ago - Health

World coronavirus updates

Data: The Center for Systems Science and Engineering at Johns Hopkins; Map: Axios Visuals

The number of COVID-19 cases surpassed 20 million worldwide on Monday evening, Johns Hopkins data shows.

The big picture: World Health Organization chief Tedros Adhanom Ghebreyesus told a virtual press conference as the world approached the milestone that 750,000 deaths were set to be recorded this week. "Every life lost matters," he said. "But I want to be clear: there are green shoots of hope and... it's never too late to turn the outbreak around."

Trump: Coronavirus is "under control"

President Trump said in an interview with “Axios on HBO” that he thinks the coronavirus is as well-controlled in the U.S. as it can be, despite dramatic surges in new infections over the course of the summer and more than 150,000 American deaths.

  • “They are dying, that's true. And you have — it is what it is. But that doesn't mean we aren't doing everything we can. It's under control as much as you can control it. This is a horrible plague,” he told Axios' Jonathan Swan.

White House will require staff to undergo randomized coronavirus testing

Photo: Alex Wong/Getty Images

Staff in the Executive Office of the President will be subject to mandatory coronavirus tests, in efforts to "protect the health and safety of the entire White House Complex," CNBC reports.

  • Why it matters: Multiple people in the White House have tested positive for COVID-19 throughout the pandemic, including President Trump's national security adviser Robert O'Brien last week.

What they're saying: “As part of our ongoing efforts to protect the health and safety of the entire White House Complex, randomized testing of Executive Office of the President staff, which has been ongoing for several months, will become mandatory rather than voluntary," a White House official said Monday.