(CNN) Just as much of the US was improving, 10 states are seeing their highest seven-day average of new coronavirus cases per day since the pandemic started months ago, according to a CNN analysis of data from Johns Hopkins University.
The data includes new cases reported by Johns Hopkins through Tuesday. The states seeing record-high averages are Alabama, Arizona, California, Florida, Nevada, North Carolina, Oklahoma, Oregon, South Carolina and Texas.
Texas also reported a record-high number of daily Covid-19 hospitalizations on Monday, with 2,326.
Los Angeles County, which accounts for almost half of California's cases, on Wednesday reported another single-day high of new cases, though officials said the spike was due to lagging test reports.
While some politicians have attributed higher case numbers to better testing, recent surges are outpacing the increase in tests, said Dr. Ezekiel Emanuel, chair of the Department of Medical Ethics and Health Policy at the University of Pennsylvania.
"You can have a small percentage increase because of testing in terms of number of cases," he said.
"But when you see 50% or 150% increase in the number of cases you are seeing -- which is what we are seeing across the South -- that's not testing. That's new cases. That's community spread."
According to data from Johns Hopkins University:
• 21 states are seeing upward trends in newly reported cases from one week to the next: Alabama, Alaska, Arizona, Arkansas, California, Delaware, Florida, Georgia, Hawaii, Kansas, Oregon, Louisiana, Montana, Nevada, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, West Virginia and Wyoming.
• Eight states are seeing steady numbers of newly reported cases: Connecticut, Indiana, Maine, Mississippi, Ohio, South Dakota, Utah and Washington.
• 21 states are seeing a downward trend: Colorado, Idaho, Illinois, Iowa, Kentucky, Maryland, Massachusetts, Michigan, Minnesota, Missouri, Nebraska, New Hampshire, New Mexico, New Jersey, New York, North Dakota, Pennsylvania, Rhode Island, Vermont, Virginia and Wisconsin.
• One state, Vermont, has seen a decrease of at least 50%.
Across the country, more than 2.1 million people have been infected with coronavirus, and more than 117,000 have died.
"We're seeing these flare-ups, these hot spots now popping up in a number of states -- particularly Texas, Florida, Arizona," said Erin Bromage, an associate professor of biology at the University of Massachusetts Dartmouth.
"Those case numbers are really going up fast. And more importantly, the number of hospitalizations in those states are increasing, which usually lags a few weeks behind the number of new cases."
Florida recorded almost 2,800 new coronavirus cases on Monday -- its highest number of new and confirmed cases in a single day, according to the Florida Department of Health.
But Gov. Ron DeSantis said the state will not shut down.
"We're going to go forward. We're going to continue to protect the most vulnerable," DeSantis said. He also urged residents to maintain social distancing and avoid crowds.
States don't need to shut down again to control the virus, Bromage said. "They just need clearer messaging to guide their population about what to do."
"Get masks on the population. We know that helps," he said.
"Reinforce the social distancing between people. And slow down this race to (fully) reopen. Because if you don't, we know that these spikes in cases -- if they keep increasing the way they are -- always precede really large cases in hospitals."
West Virginia Gov. Jim Justice reported a sixth outbreak linked to churches. Three are still active, he said.
At least 32 cases have been identified at one church in Greenbrier County, and four cases at a church in Ohio County. Justice did not say how many parishioners had tested positive at a Boone County church, the third active outbreak location.
Nine Texas mayors, including those in Houston, Dallas, Austin and San Antonio, have urged Gov. Greg Abbott to give them the authority to require masks be worn in public "where physical distancing cannot be practiced."
In a letter to Abbott, the mayors said "many people in many of our cities are still refusing to wear these face coverings even though these coverings are scientifically proven to help prevent the disease from spreading."
The governor agreed that "wearing a mask is very important" but expressed reservations about enforcement and potential punishment. "All of us have a collective responsibility to educate the public that wearing a mask is the best thing to do."
A growing number of studies show face masks reduce the spread of the coronavirus, especially because many people are contagious before they have symptoms and because this virus can spread by just talking or breathing.
Arizona Gov. Doug Ducey resisted calls from physicians across his state to mandate wearing masks in public places, saying he would leave that up to mayors to decide, because the level of transmission vary from region to region.
Montgomery, Alabama, Mayor Steven Reed issued an executive order requiring masks or face coverings to be worn in public places, a day after the city council failed to pass an ordnance with that requirement.
An estimated 230,000 to 450,000 cases of the virus were prevented in the states that enacted requirements for mask use between April 8 and May 15, a study reported Tuesday found.
"The findings suggest that requiring face mask use in public might help in mitigating COVID-19 spread," wrote Wei Lyu and George Wehby, with the Department of Health Management and Policy at the University of Iowa's College of Public Health.
Another study published in the Lancet medical journal also said wearing a face mask decreases the chances of spreading coronavirus.
A "second wave" of coronavirus could start in late August, with the US reaching more than 201,000 Covid-19 deaths by October 1, according to the Institute of Health Metrics and Evaluation at the University of Washington.
But analysts say the rates of coronavirus haven't even dropped to a level low enough to call the first wave over.
As the virus spreads, it appears to be following highways as more people go out and more places reopen, researchers from Children's Hospital of Philadelphia and the University of Pennsylvania said Tuesday. They cited south-to-north spread along I-95 on the East Coast, I-85 in the South, and I-5 and I-10 in the West, the team said.
Meantime, New York and New Jersey no longer have the highest per-capita infection rate. That would be the Navajo Nation, which spans parts of New Mexico, Utah and Arizona and has a population of about 173,600 people.
The Navajo Nation announced lockdowns over the next two weekends to try to help quash the outbreak. The first is expected Friday to Monday, and the next will take place the following weekend.
"Now is not the time to back down," Navajo Nation President Jonathan Nez said. "Wear your masks, practice social distancing, and wash your hands."
Some Americans are exhausted from the pandemic, acknowledged Dr. Ashish Jha, director of the Harvard Global Health Institute. But people can't let their guards down.
"We may be done with the pandemic," he said, "but the pandemic is not done with us."