HOUSTON (BLOOMBERG, AFP) - Texas on Wednesday (June 10) reported 2,504 new coronavirus cases, the highest one-day total since the pandemic emerged.
A month into its reopening, Florida this week reported 8,553 new cases - the most of any seven-day period.
California's hospitalisations are at their highest since May 13 and have risen in nine of the past 10 days.
A fresh onslaught of the novel coronavirus is bringing challenges for residents and the economy in pockets across the United States.
The localised surges have raised alarms among experts even as they are masked by the nation's overall case count, which early this week rose just under 1 per cent, the smallest increase since March.
"There is a new wave coming in parts of the country," said Dr Eric Toner, a senior scholar at the Johns Hopkins Centre for Health Security.
"It's small and it's distant so far, but it's coming."
The number of confirmed coronavirus infections in the US topped two million on Wednesday, according to a tally by Johns Hopkins University.
The pandemic has claimed the lives of more than 112,900 people in the US, which leads the world in the number of confirmed infections with 2,000,464, according to the Baltimore-based school's latest count.
Though the outbreaks come weeks into state reopenings, it is not clear that they are linked to increased economic activity.
And health experts say it is still too soon to tell whether the massive protests against police brutality that have erupted in the past two weeks led to more infections.
In Georgia, where hair salons, tattoo parlours and gyms have been operating for a month-and-a-half, case numbers have plateaued, flummoxing experts.
Puzzling differences show up even within states.
In California, which imposed a stay-at-home order in late March, San Francisco saw zero cases for three consecutive days this week, while Los Angeles County reported well over half of the state's new cases.
The White House Coronavirus Task Force has yet to see any relationship between reopening and increased cases of Covid-19, Food and Drug Administration Commissioner Stephen Hahn said on a podcast.
But in some states, rising numbers outpace increases in testing, raising concerns about whether the virus can be controlled.
It will take a couple of weeks to know, Dr Toner said, but by then "it's going to be pretty late" to respond.
Since the pandemic initially swept the US starting early this year, almost two million people have been infected and more than 110,000 have died.
After a national shutdown that arrested the spread, rising illness had been expected as restrictions loosened.
The trend has been observed across 22 states in recent weeks, though many increases are steady but slow.
In New York, the state hardest hit by Covid-19, Governor Andrew Cuomo only recently started reopening by region. New York City, the epicentre, began the first of four phases on Monday.
"We know as a fact that reopening other states, we're seeing significant problems," Mr Cuomo said on Tuesday.
"Just because you reopen does not mean you will have a spike, but if you are not smart, you can have a spike."
Experts see evidence of a second wave building in Arizona, Texas, Florida and California.
Arizona "sticks out like a sore thumb in terms of a major problem", said Dr Jeffrey Morris, director of the division of biostatistics at University of Pennsylvania's Perelman School of Medicine.
ARIZONA SPIKE
Arizona's daily tally of new cases has abruptly spiked in the last two weeks, hitting an all-time high of 1,187 on June 2.
This week, its Department of Health Services urged hospitals to activate emergency plans.
Director Cara Christ told a Phoenix television station that she was concerned about the rising case count and percentage of people tested who are found to be positive.
Valleywise Health, the public hospital system in Phoenix, has seen an increase in Covid-19 cases during the past two weeks.
It has expanded its intensive care capacity and those beds are 87 per cent full, about half with Covid-19 patients, according to Dr Michael White, the chief medical officer.
Dr White said Valleywise has adequate protective gear for staff, but hospitals aren't getting their entire orders.
A surge in Covid-19 cases could put that supply under stress, he said.
The increase in transmission follows steps to resume business and public life.
"Within Phoenix, we've been more relaxed than I've seen in some of the other parts of the country," Dr White said, with some people disregarding advice to wear masks and maintain 1.8m of distance from others.
"People are coming together in environments where social distancing is challenging."
Texas on Wednesday reported a 4.7 per cent jump in hospitalisations to 2,153, the fourth consecutive daily increase.
The latest figures showing an escalation came as Governor Greg Abbott tweeted a public service announcement featuring baseball legend Nolan Ryan urging Texans to wash their hands and to not be "a knucklehead".
Mr Abbott was criticised for an aggressive reopening last month.
Mobile phone data show activity by residents is rebounding toward pre-Covid-19 levels, according to the Children's Hospital of Philadelphia's PolicyLab.
That could reflect a perception that the virus wasn't "ever a big threat", said Dr Morris, who recently moved to Philadelphia after 20 years in Houston.
Florida's health department said in a statement that it attributes the increase in cases to "greatly expanded efforts in testing", and noted that overall positivity rates remain low, at about 5.5 per cent.
Bucking the trend is Georgia, which was the first US state to reopen. Covid cases there have plateaued.
Despite local outbreaks in the state, "their sea levels did not rise", said Dr David Rubin, director of the PolicyLab, which has been modelling the virus' spread.
"They've kind of held this fragile equilibrium."
CREEPING IN
California was the earliest state to shut down its economy over the coronavirus, after one of the nation's first outbreaks in the San Francisco Bay Area. It has been slower than most to reopen.
Even so, the state has also seen the number of people hospitalised with Covid-19 rebound in the past two weeks, as commerce accelerates.
Case counts are climbing too, although officials attribute that to increased testing and say it's a sign of preparation.
In part, rising numbers represent the virus spreading into places that largely avoided the first round of infections, including rural Imperial County in California's south-eastern desert.
Yet the contagion remains present in places that bore the brunt of the first wave, including Los Angeles County.
Hospitalisations there are lower than at the start of May, but deaths remain stubbornly high, with 500 in the past week alone.
Dr Barbara Ferrer, Los Angeles County public health director, said the region has likely not seen the end of the first wave.
And despite concerns about infections coming out of mass demonstrations in the sprawling city, she thinks the reopening of the economy will have a bigger impact.
"We're not at the tail end of anything," Dr Ferrer said.
"We never had a huge peak. We've kind of been within this band. We're not in decline, we're kind of holding our own in ways that protect the healthcare system."
But, she added, "go to Venice and see the crowds, and you'll understand why I have concerns".
ANOTHER ONSLAUGHT
The US has long been bracing for another wave, but future outbreaks are likely to take a different shape.
Social distancing and mask-wearing, as well as careful behaviour by individuals, are likely to have staying power even as economies reopen.
Experts are steeling for autumn, when changes in weather and back-to-school plans could have damaging repercussions.
"The second wave isn't going to mirror the first wave exactly," said Dr Lance Waller, a professor at Emory University's Rollins School of Public Health in Atlanta.
"It's not snapping back to exactly the same thing as before, because we're not exactly the way we were before."
Dr Daniel Lucey, a fellow at the Infectious Diseases Society of America, compared the virus' new paradigm with a day at the beach: The US has been bracing for another "high tide" like the one that engulfed New York City. Today is a low tide, but "the waves are always coming in".
