Only one Pi Beta Phi member was showing symptoms and none of her sorority sisters were being allowed to leave the off-campus house, officials said.
“At this point, no members have been hospitalized and any who are ill are experiencing minor effects of the virus,” Pi Beta Phi strategic initiatives director Shawn Eagleburger said in a statement.
The sorority sisters who moved into the Pi Beta Phi house between Aug. 2 and Aug. 6 all tested negative for COVID-19, Eagleburger said.
But as Pi Beta Phi embarked on a virtual recruitment drive to attract new pledges, some of the sorority sisters let their guard down.
“Eager to reconnect with friends, on August 11, a small group of members who reside outside of the facility joined the chapter for a short, informal gathering at the facility,” Eagleburger wrote. “On August 12, the Chapter President was informed one of these members was experiencing symptoms of COVID-19; the member later confirmed she had tested positive. On August 14, members who since began experiencing symptoms were tested; many tested positive.”
University spokeswoman Monica Roberts said the campus was bracing for this possibility of mass infections.
“This was expected,” Roberts told The Daily Oklahoman on Saturday. “When you bring back 20,000 students, there will invariably be more cases related to campus. We’ve prepared for this for five months and have protocols in place to manage the situation. Our priority is the safety and well-being of our campus community and transparency in communications.”
The lockdown at Pi Beta Phi came as Oklahoma has seen a surge in new COVID-19 infections, averaging close to 800 new cases per day in the last four weeks, according to an NBC News analysis of available figures.
Among those infected last month was Oklahoma Gov. Kevin Stitt, a Republican and ally of President Donald Trump who was criticized for his cavalier approach in the early days of the unfolding crisis. So far, Oklahoma has reported 48,342 cases and 661 COVID-19 deaths since the start of the pandemic.
Nationally, the number of confirmed COVID-19 cases was nearing 5.5 million and the death toll as of Monday morning was over 171,000, according to the NBC News numbers. The U.S., which leads the world in both categories, has accounted for roughly a quarter of the 22.5 million cases and 776,000 deaths across the globe.
"It's going away," Trump told reporters for the umpteenth time at Minneapolis-St. Paul International Airport. "But, we’re also going to have vaccines very soon."
Most of the new cases and deaths in the U.S. have been in Southern and Sun Belt states that reopened at the urging of the Trump Administration as the numbers of new COVID-19 cases were starting to climb.
Florida has been hit especially hard in recent months. For the 76th day in a row, the state health department Monday reported more than 1,000 new cases. And the Sunshine State was on track to soon join California as the only states with more than 600,000 confirmed cases, NBC News figures showed.
As of Monday afternoon, Florida had also reported 9,586 deaths.
The American Health Care Association and National Center for Assisted Living said in an updated report Monday that there has been a "major spike in new COVID cases" that has now surpassed the previous peak level on May 31 and that 78 percent of them are in Sun Belt states.
While nursing home deaths from the coronavirus had been declining, they are on the rise again and 69 percent of deaths in late July occurred in Sun Belt states, the report concluded.
A version of this story originally appeared on NBCNews.com.