(CNN) Officials in states across the South are warning that more young people are testing positive for coronavirus.
The shifts in demographics have been recorded in parts of Florida, South Carolina, Georgia, Texas and other states -- many of which were some of the first to reopen.
And while some officials have pointed to more widespread testing being done, others say the new cases stem from Americans failing to social distance.
In Mississippi, where one health officer called adherence to social distancing over the past weeks "overwhelmingly disappointing," officials attributed clusters of new cases to fraternity rush parties.
Texas Gov. Greg Abbott said last week that people under 30 made up a majority of new coronavirus cases in several counties. He said that increase in young infected people could be related to Memorial Day parties, visits to bars or other gatherings.
And in Florida, Gov. Ron DeSantis said Friday that the median age was 37 for newly diagnosed coronavirus cases over the last week. In the state, 62% of new cases for the week of June 7 are under 45 years old, he said.
"That is a big change from where we were at the end of March and the beginning of April. It was skewing much older at that time," he said.
Coronavirus has more severe outcomes on older people, Blacks and Hispanics, and people with underlying health conditions, according to demographic data from the US Centers for Disease Control and Prevention. From the beginning of the pandemic up through May 30, the median age of positive coronavirus cases was 48, the CDC said.
Given the case increases, the CDC has been conducting a scientific review about the public health benefits of masks, and will soon make an updated recommendation, a senior CDC official told CNN.
A senior official with knowledge of the review said science is being studied as to whether masks are not only "good for source control -- and keeping you from giving it to others -- but we're also seeing if masks are going to protect you from getting [Covid-19] yourself."
"We know it's a good thing to wear a mask to protect others. We are studying if it is also potentially going to keep you safe," the official added.
The CDC website has two separate pages of guidance on face coverings. One recommends people wear masks when they leave their home. The other recommends people wear a mask if they cannot properly social distance.
So far, the US has recorded more than 2.27 million cases and at least 119,921 deaths, according to Johns Hopkins University.
In Florida, Gov. DeSantis said Saturday cases are "shifting in a radical direction" toward populations in their 20s and 30s.
Those younger groups testing positive are mostly asymptomatic and don't require clinical attention, the governor said.
"We're also seeing that not only are they testing positive because they're testing more, they're also testing positive at a higher rate increasingly over the last week," DeSantis said, adding there's evidence of transmission between those younger groups.
That increased testing, he said, comes as many people are returning to the workforce.
Experts have raised alarm about Florida's climbing cases, saying the state could become the next US coronavirus epicenter. On Saturday, Florida reported 4,049 new cases -- the most reported in a single day.
In South Carolina, health officials said Friday people under the age of 30 were increasingly testing positive for the virus -- around 18% of the state's total cases come from people between the ages of 21 and 30.
"The increases that we're seeing serve as a warning that young adults and youth are not immune to Covid-19," said Dr. Brannon Traxler, the state's Department of Health and Environmental Control physician consultant. "They also tell us that younger South Carolinians are not taking social distancing seriously."
And Georgia's largest hospital also reported seeing an increase in patients in their 20s and 30s, according to CNN affiliate WSB.
"It's a little bit of a disturbing trend, and what frightens me is not only that they are younger, the potential of them infecting other people, particularly parents and grandparents," Dr. Robert Jansen, chief medical officer at Grady Health System, told WSB.
Despite stark warnings from experts across the US, hundreds gathered Saturday in Tulsa, Oklahoma, for President Donald Trump's first re-election campaign rally since the start of the pandemic.
Few donned masks even as Tulsa County reported its highest number of new infections in a day Saturday -- the fifth time this week the country reported a record.
The Texas Alcoholic Beverage Commission said Sunday it has suspended the permits of 12 bars found to be in violation of the state's Covid-19 reopening protocols.
The commission issued 30-day permit suspensions to bars in Houston, Dallas, Fort Worth, Austin and other cities.
In Galveston County, Texas, Dr. Philip Keiser with the local health department told CNN affiliate KPRC they were seeing a lot of infections in young people.
And the age of the people testing positive is trending younger, he told the news station.
"Our average age last week of people that were positive was age 30, the average age of people getting tested was 47," he said.
And those numbers come as many haven't followed guidance issued by health officials urging residents to keep their distance and wear face coverings.
"We have data from some of the cell phone companies that show in Galveston County less than 7% of the people are social distancing," Keiser said.
Galveston County is home to about 342,139 people, according to the US Census Bureau.
According to data from Johns Hopkins University, at least 23 states are trending upward in new cases compared to last week. Ten of those states reported more than a 50% jump -- including Texas and Florida, which were some of the first states to begin reopening.
California, the first state to enforce sweeping lockdown measures, is also seeing an increase in cases. On Saturday, the state reported 4,515 new coronavirus cases, the most in a single day.
And more Californians were hospitalized Saturday -- 3,574 -- than at any time since the pandemic started, state data shows. The number of patients being treated in intensive care units with Covid-19 has risen to the highest number since May 3.
As some states report record numbers of daily new cases and state leaders mull implementing face mask requirements, the World Health Organization warned the pandemic is accelerating.
More than 150,000 new cases of the virus were reported to WHO Thursday, the organization's director-general, Tedros Adhanom Ghebreyesus said in a Friday news conference.
Almost half of those cases were reported from the Americas, he said.
"The world is in a new and dangerous phase. Many people are understandably fed up with being at home. Countries are understandably eager to open up their societies and economies. But the virus is spreading fast, it is still deadly, and most people are still susceptible," he said.