This story was reported by Alfonso A. Castillo, Matthew Chayes, Lisa L. Colangelo, Michael Gormley and Candice Ferrette. It was written by Colangelo.

New York State will send the National Guard to New Rochelle as part of a "containment" plan to slow the spread of coronavirus in that Westchester city, which has become the center of the state's outbreak, Gov. Andrew M. Cuomo said Tuesday.

Suffolk County said Tuesday night it had three more positive test results, raising the county's coronavirus count to four cases.

County Executive Steve Bellone said the confirmed cases concerned a man in his early 20s, in isolation at Stony Brook University Medical Center; a Southold woman in her early 20s, in isolation at home; and a man in his 80s, in isolation at St. Catherine's Hospital in Smithtown. Suffolk's other COVID-19 patient was hospitalized at Southampton Hospital.

One of the four who tested positive works for Peconic Landing in Greenport, the nursing home said in a statement. Bellone said the county's communicable disease professionals are investigating the patients' contacts.

"While we continue to do all that we can to avoid a widespread outbreak, we are asking the public to do the same," Bellone said in a statement. "If you are sick, stay home and contact your primary care physician to avoid spreading any illness to others."

Nassau County added two cases, bringing its total to 19, Laura Curran, the county's executive, said at a separate Tuesday morning news briefing.

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The number of confirmed cases of coronavirus in New York has increased to 173, Cuomo said. More than 100 people have tested positive for the virus in Westchester County alone.

Suffolk also said it is monitoring 72 individuals under precautionary quarantine and has eight other individuals under mandatory quarantine, with 11 pending test results.

Cuomo admitted creating a containment zone was a "dramatic" action.

“New Rochelle is a particular problem … the numbers are going up unabated,” he said at a news briefing in Albany. “It is the largest cluster in the country. It is a matter of life and death.”

The virus can cause mild to severe respiratory illness and is especially dangerous for the elderly and people with underlying health conditions.

The number of confirmed cases in New York City grew to 36, with 1,980 people in voluntary isolation and 30 others in mandatory quarantine, New York City Mayor Bill de Blasio said Tuesday afternoon.

People looking to board cruise ships at the city's terminals in Manhattan and Red Hook, Brooklyn, will be turned away if they have temperatures over 100.4 degrees, he said. Any passengers who leave cruise ships docked in the city found to have a temperature of 100.4 degrees or above will be taken to a hospital or asked to self isolate.

"This is not a good time to take a cruise," de Blasio said.

Around the region, schools have closed and large events been postponed as a reaction to the growing spread of the virus. The New York Auto Show, scheduled to take place at the Javits Center in April, was moved to late August, and the New York Half Marathon on Sunday was canceled.

The containment plan — which starts Thursday — targets a one-mile radius surrounding a New Rochelle synagogue, in an area that New York State Health Commissioner Howard Zucker called "the center of the activity" for the outbreak. For two weeks, schools, houses of worship and other large gathering places will be closed or restricted within the containment area, but people can move about freely and stores will remain open, Cuomo said.

The National Guard will help deliver food and clean public spaces.

“You are not containing people, it’s facilities,” he said

A New Jersey man died from the virus, Gov. Phil Murphy said Tuesday. The man was in his 60s and lived in Bergen County.

Also Tuesday, New York Attorney General Letitia James ordered two New York City merchants to stop overcharging for hand sanitizers and disinfectant sprays. James said investigators confirmed Scheman & Grant Hardware, doing business as Ace Hardware, in Midtown Manhattan was charging customers $79.99 for 1200 mL or a 40-ounce bottle of hand sanitizer. City Fresh Market in Astoria was found to have charged $14.99 for a 19-ounce bottle of disinfectant spray.

The Nassau County Office of Consumer Affairs has taken action against several retailers since announcing a crackdown on coronavirus-related price-gouging. All the cases involved improperly charging for protective masks.

Curran said two of the county's new positive cases were school bus drivers. Officials have reached out to the families of the 80 children they were in contact with on their routes.

There are currently 72 people on mandatory quarantine and another 74 under precautionary quarantine in Nassau. Tests results on an additional 10 people are pending, officials said.

A 'volatile situation'

Northwell Health Labs has received federal approval to establish a satellite testing facility within the containment circle, Cuomo said.

“This is a volatile situation,” Zucker said. “We have moved from a containment strategy to a mitigation strategy.”

Both de Blasio and Cuomo emphasized the sick and elderly are most at risk for contracting serious illness from the virus, while younger, healthy people will more easily recover or may not even develop severe symptoms.

Cuomo said just 14 of 173 people with the virus in the state are hospitalized, and most of them are elderly or previously ill. The state may order some or all nursing homes to limit or suspend visitation in the future as the outbreak continues. Many nursing homes and assisted living facilities are already closed to visitors.

“It’s always the vulnerable population,” Cuomo told WAMC. “All you need is one 8-year-old Johnny to go into a nursing home and see his grandma and hug and kiss grandma and you are off to the races.”

De Blasio said there are no plans to cancel the city's traditional St. Patricks Day Parade on Fifth Avenue. Earlier Tuesday, Cuomo said in an interview on CNN's "New Day" that officials were considering canceling the parade after Boston did as part of continued precautions against spread of the virus. Hours later at his Albany news conference, he urged communities to consider the size of the outbreak in their locale in deciding whether to hold St. Patrick's Day parades.

The parade is scheduled for March 17. A phone message left Tuesday morning with the parade organizer was not immediately returned, but within an hour of Cuomo's interview, the official parade website was updated with a COVID-19 "virus note": "We have received no communications from the authorities concerning the possibility of a postponement at this point. We recommend checking with your local health officials, government, and where appropriate, your personal physician for guidance."

During a news conference and several media interviews Tuesday, Cuomo reiterated his call for the United States to ramp up its testing of potential cases, noting that China tests about 10,000 samples a day.

“How does China and Korea have a better, faster testing than we do?” he said on CNN's "The Lead with Jake Tapper." In contrast, 5,000 cases in total have been tested in the United States since the outbreak.

"That's the scale you need to keep ahead of this beast or you are playing catch-up from Day One. And that’s what we’re doing, playing catch up.”

Contradictory messages

Cuomo tried to clarify what he said has been confusing and sometimes contradictory messages about precautions coming from Vice President Mike Pence and President Donald Trump.

“Let’s remember the bottom line here. The vulnerable population should be taking precautions,” Cuomo said. He said those precautions for the elderly and ill include “thinking twice” about boarding aircraft and avoiding large gatherings of people.

During an early Tuesday morning television appearance on MSNBC's "Morning Joe," de Blasio cautioned against "an overreaction."

"We are better off keeping our society together, our economy together, our schools open. We're better off not closing larger events, because from what we're seeing you don't get this disease by walking into an arena where someone else in that area has it," de Blasio said. "You only get this disease if you're right up on that person and somehow they cough or sneeze really right up on you."

Earlier this week, de Blasio said New Yorkers should stay off the subways "if you can."

De Blasio's advice has shifted from early in the outbreak, when he said a week prior that the virus could be contracted only from prolonged contact and that, "The subway is not the issue. The train is not the issue. The issue is prolonged, consistent contact."

He said the cases in New York City were driven mostly by a lawyer in Westchester who has been diagnosed with the virus. His cluster has been what de Blasio called "the Number 1 generator."

Transportation dip

Long Island Rail Road commuters and transportation officials said there was a noticeable dip in public transportation ridership as companies allowed employees to work from home.

Although the LIRR and its parent agency the Metropolitan Transportation Authority have not provided updated ridership figures, MTA chairman Patrick Foye, in an interview with WCBS radio Tuesday, said the number of commuters is "trending down, I think, probably in the single digits."

The MTA will report its latest ridership data at its monthly board meeting March 23, agency officials said.

Fred Geiger said the “parking lot was empty” when he arrived at the Lindenhurst station to catch his usual 5:17 a.m. train to Penn Station.

“Usually, there’s at least some cars,” said Geiger, 46, a maintenance engineer in Manhattan’s Lower East Side.

Stepping off an LIRR train at Garden City station, which had plenty of empty parking spots Tuesday afternoon, Neil Borden said he wasn't overly concerned about the virus.

"If it's going to happen, it's going to happen. I wash my hands," said Borden, a Bronx resident. "I'm not afraid. I'm 62. I'm in good health."

Anthony Simon, general chairman of International Association of Sheet Metal, Air, Rail and Transportation Workers, the LIRR’s largest union, sought to reassure members as they set about an aggressive campaign to disinfect the entire fleet of train cars every 72 hours, and its 124 stations every day.

In a memo, Simon said his union’s “highest priority is the safety of our customers and employees, while understanding its responsibility to move trains and clean our fleet during this concerning time.”

Recent cases

A lawyer from New Rochelle, linked to a cluster of cases, is hospitalized in Manhattan. Cuomo said the man is recovering, although still in intensive care.

Officials said the confirmed cases of coronavirus in New York State included the executive director of the Port Authority and an EMS worker with the FDNY — the first confirmed case of a first responder who tested positive, according to his labor union.

According to the World Health Organization, there were 113,702 cases globally as of Tuesday, with 4012 deaths. The majority — 80,924 cases and 3,140 deaths — are in China.

The virus has infected 647 people in the United States, and at least 25 have died, according to the CDC.