Florida’s biggest county ordered restaurants and gyms closed again Monday because of a rise in confirmed coronavirus cases and hospitalizations, as the U.S. emerged from a Fourth of July weekend of picnics, pool parties and beach outings that health officials fear could fuel the rapidly worsening outbreak.

The see-saw effect — restrictions lifted, then reversed after a resurgence of cases — has been seen around the U.S. in recent weeks and is expected again after a long holiday that saw party-goers and sunbathers gathering, many without masks, on one of the biggest weekends of the summer.

Confirmed cases are on the rise in 41 out of 50 states plus the District of Columbia, and the percentage of tests coming back positive for the virus is increasing in 39 states.

Florida, which recorded an all-time high of 11,400 cases Saturday and has seen its positive test rate over the past two weeks reach more than 18%, has been especially hard hit, along with other Sunbelt states such as Arizona, California and Texas.

In Florida’s Miami-Dade County, population 2.7 million, Mayor Carlos Gimenez issued an emergency order closing restaurants and certain other indoor places, including gyms and vacation rentals, seven weeks after they were allowed to reopen.

“We want to ensure that our hospitals continue to have the staffing necessary to save lives,” Gimenez said in a statement.

Hair salons and stores will remain open along with hotel pools and summer camps. Beaches will reopen in the county on Tuesday after they being closed over the weekend. “But if we see crowding and people not following the public health rules, I will be forced to close the beaches again,” the mayor warned.

Hospitalizations across the state have been ticking upward, with nearly 1,700 patients admitted in the past seven days compared with 1,200 the previous week. Five hospitals in the St. Petersburg area were out of intensive care unit beds, officials said. Miami-Dade said it has more than 1,600 coronavirus patients now in the hospital, more than double from two weeks ago.

“If we continue to increase at the pace we have been, we won’t have enough ventilators, enough rooms,” said Dr. David De La Zerda, a respiratory specialist at Miami’s Jackson Memorial Hospital.

Officials in Texas said hospitals are in danger of being overwhelmed. Hospitalizations statewide surged past 8,000 for the first time over the Fourth of July weekend, a more than fourfold increase in the past month. Houston officials said intensive care units there have exceeded capacity.

Along the border with Mexico, two severely ill patients were flown hundreds of miles north to Dallas and San Antonio because hospitals in the Rio Grande Valley were full.

In Arizona, the number of confirmed cases has surpassed 100,000, and more than half of those infected, or over 62,000, are under 44, state health officials said.

Around the country, health officials have warned that the surge is being driven in large part by younger people who are disregarding the social distancing rules and that they could easily spread it to older, more vulnerable people, such as their parents and grandparents.

The coronavirus is blamed for over a half-million deaths worldwide, including more than 130,000 in the U.S., according to the tally kept by Johns Hopkins University. The number of confirmed cases in the U.S. stood at about 2.9 million, though the real number of infections is believed to be 10 times higher.

Over the past few days, new cases per day nationwide have hit record levels well over 50,000. On average, the daily count has surged more than 80% over the past two weeks, according to an Associated Press analysis.

Average deaths per day have fallen over the same period from around 600 to about 510, reflecting what experts say are advances in treatment and prevention and the large share of cases among young adults, who are more likely than older ones to survive COVID-19.

But deaths are considered a lagging indicator — that is, it takes time for people to get sick and die. And experts are worried the downward trend in deaths could reverse itself.

Meanwhile, three of the top U.S. medical organizations issued an open letter urging Americans to wear masks, social distance and wash hands often to help stop “the worst public health crisis in generations.”

The American Medical Association, American Nurses Association and American Hospital Association issued the plea in the absence of a mask-wearing order from Washington and said steps taken early on that helped slow the spread of COVID-19 “were too quickly abandoned.”

The White House again rejected calls for a nationwide order to wear face coverings. Appearing on “Fox and Friends,” White House chief of staff Mark Meadows said that President Donald Trump sees the issue as a state matter.

“We’re allowing our local governors and our local mayors to weigh in on that,” he said.

In New York City, once the most lethal hot spot in the country, nail salons and dog runs were allowed to reopen but indoor dining was postponed indefinitely.

Mayor Bill de Blasio said about 50,000 more people will come back to work as the city enters Phase 3 of reopening, covering tattoo parlors, indoor tanning and sports such as basketball, volleyball and handball.

“It will be more of summer again because we did this hard work to get this far and we cannot let up now,” he said.

New York Gov. Andrew Cuomo said he was concerned about reports of large gatherings over the holiday weekend in New York City, on Fire Island and in some other places.

“I understand people are fatigued,” he said. “We’ve been doing this for 128 days. I get it. But it doesn’t change the facts, and we have to stay smart.”

(AP)