About two weeks ago, New Jersey’s governor, Philip D. Murphy, urged residents with second homes not to decamp to the shore.
When it became clear that his message had not been fully received, the governor took things a step further: He authorized towns and counties to restrict or prohibit rentals at hotels, motels and short-term lodging to stop travelers from transmitting the virus.
“No one should be leaving their primary residences,” Mr. Murphy said last weekend.
But many already had.
As the coronavirus exploded in New York City, leaders and residents of areas that are seasonal refuges and second homes for city dwellers called for outsiders to stay away. They feared that an influx of people could strain resources, from supermarkets to parks, and potentially overwhelm small exurban hospitals.
That influx of unwanted visitors did not change the virus’s path, which has followed a logical pattern of infection, growing outward from the epicenter of New York City.
It also did not cause an outbreak: Although Suffolk County on Long Island now has the fourth-most confirmed cases among the state’s counties, the caseload remains low in the Hamptons.
Yet preliminary data and anecdotal evidence does suggest that fleeing New Yorkers may have hastened the virus’s spread.
At the southern tip of New Jersey in Cape May, a quaint seaside resort filled with picturesque Victorian mansions and bed-and-breakfasts, a 30-year-old man from New York City was identified on March 18 as the county’s first confirmed case of the virus.
In Greene County, N.Y., home to the Catskill Mountains, the first four confirmed coronavirus cases were all people from New York City.
“I don’t want to give out a false notion that because we have 31 confirmed that we are somehow dodging this pandemic; we are not,” said Shaun Groden, the Greene County administrator.
Mr. Groden and other county leaders have emphasized how their county has no hospital, even highlighting that fact in an official statement warning New Yorkers and people from Westchester to stay away. He said that about 30 percent of the county’s residences are second homes, most of which appear to be occupied now.
“If I was in New York City and I had a place up here, I’d be here,” he said. “But I’m not going to come here with some false sense of security that once you get upstate, you’ll be taken care of. It’s just the opposite.”
Throughout the region, the virus seems to be mostly following a logical pattern of infection, growing outward from its epicenter of New York City. But there have also been small bursts of flulike symptoms in areas where New Yorkers have summer homes, like the Adirondacks, the Jersey Shore, the Catskills and the Hamptons.
In mid-March, the rate of people with flulike symptoms in those areas was about double what would be normal for that time of year, according to data collected by Kinsa, a company that has used internet-connected thermometers to accurately identify coronavirus hot spots before they emerge.
“It might not have emerged yet into deaths or I.C.U. beds being filled,” said Marynia Kolak, the assistant director for health informatics at the Center for Spatial Data Science at University of Chicago, which launched the Covid-19 Atlas to analyze positive diagnoses relative to area population to identify emerging outbreaks.
“But compared to all the other Covid cases in the rest of the country, at a county level, these areas are already flagged as hot spots,” she added.
Concerned municipalities have tried to stem the flow: Many Jersey towns that hug the Atlantic Ocean have closed their beaches and boardwalks in an effort to keep visitors from the north away. On Long Beach Island, a barrier island about an hour and a half from Manhattan, rentals of less than 21 days have been banned.
“The second-home people think that it’s Fourth of July,” said Joseph Mancini, the mayor of Long Beach Township, N.J., which this week joined several other shore towns in closing its beaches to nearly everyone but residents. “They’re out riding, biking, playing on the beach — not social distancing.”
In New York’s Adirondack mountain region, the Regional Office of Sustainable Tourism has shifted its message to urging visitors to stay away instead of encouraging them to come.
“Do we want you to be here? Of course!” its online fliers read. “But for now, we hope you are staying healthy and enjoying outdoor opportunities close to home.”
While there has not been a documented case of the coronavirus in the 17 resort communities on Fire Island, the 32 mile-long strip of barrier islands only accessible by boat from Long Island, several mayors have urged visitors not to come.
But Charles Sherman, the owner of the Davis Park Ferry, which offers access to the island’s easternmost tip, went a step further: On March 20, he suspended all trips for his passenger boats, a decision he said he made in conjunction with the Davis Park Association, a homeowners group.
“We are a small community on Fire Island. The fire department is not there, there are no medical people over there,” Mr. Sherman said. “It was the prudent thing not to run at all. We are protecting it.”
Nevertheless, he said he had watched some people cross from the mainland in private boats.
And in Cape May, where the 30-year-old man from New York City tested positive at a local health care facility while visiting, year-round residents regularly call the offices of elected leaders to report out-of-state plates, according to a government official familiar with the calls.
“Folks from out of state need to understand the critical need to follow stay-at-home orders,” said State Senator Michael L. Testa Jr., a Republican who represents New Jersey’s southernmost district, which cuts across Cape May and Atlantic Counties. “It’s up to them to save their fellow Americans.”
The push to keep New Yorkers at their primary residences extends beyond the metropolitan area: Late last month, the governor of Florida, where many New Yorkers have vacation homes, mandated a 14-day quarantine for anyone who had arrived from the New York region in the previous three weeks.
Similar concerns have even cropped up internationally: On Sunday, Scotland’s chief medical officer resigned after it emerged that she had violated the country’s lockdown rules by visiting her second home by the sea.
The deluge has sent resort towns scrambling to prepare for the virus. Stony Brook Southampton Hospital said it had tripled its number of intensive care beds, to 21, and hired 40 additional nurses, housing them in a local hotel.
Catskill, a village about 35 miles south of Albany, has been training its public works employees to drive ambulances and operate its ladder truck in preparation for a run on services, said Vincent Seeley, the village president.
On the ground, residents fear the virus has spread beyond the handful of cases that may be officially recorded. In East Hampton, where cases more than doubled over the past week, to 83, Kamal Jackson, a volunteer firefighter, said calls from dispatch of “FC,” fever cough — now often code for potential coronavirus — have come over his transponder nearly every day for the last three weeks.
“It was imported from somewhere else,” said Mr. Jackson, 40, who also works for a pool maintenance company and does construction work. “I don’t fault them. They own property; they have a right to be here. But it was definitely brought out here from them.
Leaders from across Suffolk County, on the eastern half of Long Island, sent a letter to Gov. Andrew M. Cuomo on March 27, asking for official restrictions on travel to the area. The governor said on Sunday that he had not “heard any local officials raise concerns” about the need for more travel restrictions and had not yet considered introducing them.
The Shinnecock Indian Nation, a tribe whose leaders signed the letter to the governor and whose 980-acre reservation is at the westernmost edge of the Hamptons, is trying its own tactic: On the edge of Sunrise Highway, the tribe’s large electronic billboards scroll President Trump’s recent advisory that residents of New York, New Jersey and Connecticut “refrain from nonessential domestic travel for 14 days.”
“It feels like we have been invaded and they are taking advantage of our enclave,” said Bryan Polite, the chairman of the tribe. “Those people were selfish, and we have to deal with the ramifications of their actions.”
Donald G. McNeil Jr. and Azi Paybarah contributed reporting.