(CNN) The major thrust of new coronavirus cases in the United States is in the South and West, where officials say more young people are ignoring social distancing measures and testing positive.
Young people are more likely to have milder outcomes from coronavirus, but they can still infect others who are more at risk.
"With younger age of recent infections in at least some places such as Florida, expect a lower death rate in this wave ... until the 20-40 year olds who are infected today go on to infect others," Dr. Tom Frieden, former director of the US Centers for Disease Control and Prevention, said on Twitter.
Dr. Anthony Fauci, the nation's top infectious disease expert, told Axios that the recent high number of cases in young people is "not surprising." Like Frieden, he warned of what's to come.
"They get infected first, then they come home, and then they infect the older people. The older people get the complications, and then they go to the hospitals," Fauci said. "The death rate always lags several weeks behind the infection rate."
The focus on young coronavirus-positive patients comes as nearly half of states are reporting a rise in new positive cases and some continue to break records in their daily reported cases. Florida on Monday surpassed 100,000 total coronavirus cases, according to data released by the Florida Department of Health.
In California, more than 35% of confirmed cases have been recorded in just the past two weeks, Gov. Gavin Newsom said in a news conference Monday.
The increases highlight America's systemic failure to control the pandemic, a sharp contrast to its trajectory in Europe and Asia. There, coronavirus cases sharply increased in early 2020, were met with fierce efforts to stop its spread and have since rapidly declined.
In the US, the first wave of coronavirus isn't over. In fact, cases took just a small dip and are now increasing months after the pandemic hit American shores.
"I don't think we have the luxury of talking about a second wave right now because we have not gotten out of the first wave," CNN chief medical correspondent Dr. Sanjay Gupta said. "And it's not clear that we will get out of the first wave. Instead of actually having a true ebb and flow, it may just be micro and macro peaks for the foreseeable future."
The pandemic shows no signs of weakening in the US, said Michael Osterholm, head of the Center for Infectious Disease Research and Policy at the University of Minnesota in Minneapolis.
"I think this is more like a forest fire. I don't think that this is going to slow down," Osterholm told NBC's Chuck Todd during an appearance on "Meet the Press" on Sunday.
"I think that wherever there's wood to burn, this fire's going to burn -- and right now we have a lot of susceptible people," Osterholm said. "Right now, I don't see this slowing down through the summer or into the fall. I don't think we're going to see one, two and three waves. I think we're going to just see one very, very difficult forest fire of cases."
Across the US, experts are highlighting the need for social distancing and face coverings. But parts of the country remain divided on wearing face masks in public, and more officials have had to consider making face covers in public a requirement.
"Masking has become controversial. It shouldn't be," Dr. Scott Gottlieb, former commissioner of the US Food and Drug Administration, said on CBS' "Face the Nation" Sunday. "It's a simple intervention. It's a collective action we can all take to help protect our fellow citizens and also protect ourselves and try to reopen the economy safely."
Miami on Monday made wearing a mask in public mandatory, even outdoors. The order will go into effect immediately, Mayor Francis Suarez said at a news conference Monday.
As those discussions take place, the US Centers for Disease Control and Prevention says it will soon make an updated recommendation on the public health benefits of masks, a senior agency official told CNN.
The CDC has so far been conducting a scientific review on the topic, and a senior official with knowledge of the review says researchers are studying 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."
Dr. Zeke Emanuel, who was a health care adviser to President Barack Obama and is a current adviser to Joe Biden's presidential campaign, said the initial resistance to widespread mask usage was wrong.
"Closing down businesses -- it's clear what the cost is. Wearing a mask -- there's no cost. And I think we got it wrong," he said.
Across the South, some officials are raising alarm about an increased number of younger people testing positive for the virus.
In Texas, the governor said last week 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 Saturday cases are "shifting in a radical direction" toward populations in their 20s and 30s. Those younger groups, he said, are mostly asymptomatic and don't require clinical attention.
Experts have raised alarm about Florida's climbing cases, saying the state could become the next US coronavirus epicenter. The number of coronavirus cases reached a milestone Monday as the state reported 100,217 cases, according to data released by the Florida Department of Health.
Saturday, Florida reported 4,049 new cases -- the most reported in a single day.
There are 23 states seeing a rise in new reported cases compared to the previous week, according to data from Johns Hopkins University, led by California, Texas, Florida and Arizona.
In California, the number of people hospitalized with coronavirus is the highest it's been since the beginning of the pandemic, and there have been three single-day highs of new cases recorded in the past week, according to the state department of health.
Newsom announced last week residents were required to wear a face covering in "high risk" settings, including indoor public space, public transportation or while seeking medical care.
In Texas, one of the first states to push forward with reopening, one mayor said he wished the state reopened more slowly while following coronavirus restrictions.
"When the governor started reopening, I wish he had done it a little slowly so we could have seen the numbers in each one of the phases before we moved on to the next phase," Austin Mayor Steve Adler said Sunday night.
Arizona, where President Trump plans to travel on Tuesday, continues to see its new case numbers climb. The state averaged about 2,412 new reported cases per day over the week ending June 21, up about 94% from the previous seven-day period, according to a CNN analysis of data from Johns Hopkins University.
Meanwhile, 17 states are reporting a decline in new cases. They are Alabama, Alaska, Connecticut, Illinois, Louisiana, Maine, Maryland, Massachusetts, Mississippi, New Hampshire, New Jersey, New York, North Carolina, Pennsylvania, Rhode Island, South Dakota and Vermont.
In New York City, once the epicenter of the crisis, the second phase of reopening began Monday. The phase two reopening means outdoor dining, barbershops and hair salons, playgrounds, offices and curbside retail stores can welcome customers.
New York Mayor Bill de Blasio said he plans to dine outdoors at a restaurant Monday night.
"The world of NY restaurants is very, very personally important to me," he said. "I'm very excited that this day has come."
With cases so low in the state but rising elsewhere, Gov. Andrew Cuomo said New York may consider forcing visitors from high-transmission states to quarantine upon arrival.