Updated Thursday, March 12 at 8:35 p.m. to add word that a local mother and son have tested negative and that local stores saw big crowds.

ROCHESTER, N.Y. — The first coronavirus infection in western and central New York was confirmed late Wednesday night in a Rochester man, Monroe County officials announced.

The test results triggered an aggressive attempt to identify the man's associates, some of whom have already been placed in quarantine. Health investigators are tracing more people who might have been exposed in hopes of short-circuiting the local spread of COVID-19, the disease caused by the novel coronavirus.

© Shawn Dowd Dr. Michael Mendoza, Monroe County public health commissioner provides details about the first confirmed case of COVID-19

The patient who tested positive for the virus was in isolation at home and "recovering nicely," County Executive Adam Bello said. There was no immediate indication that the man passed the virus to anyone locally, though that investigation was on-going.

"There is no immediate threat to the people of Monroe County," Bello said at a Thursday morning news conference.

Officials are sure the man contracted the virus during a recent visit to Italy, where more than 12,000 people have been infected and 825 have died. The man traveled from Rome to JFK International Airport, and took "ground transportation" to Rochester on Tuesday, officials said.

He was treated at Highland Hospital on Tuesday afternoon under closely controlled conditions in the hospital's special "decontamination room." Samples were collected then for coronavirus testing.

In a bit of good news, a mother and son who had visited Italy last month said Thursday evening that their coronavirus tests had come back negative. County officials said at 5:30 p.m. Thursday there were no new confirmed cases of COVID-19 in the county.

But confirmation of that first local case also led Dr. Michael Mendoza, the county public health commissioner, to recommend that people consider canceling any gathering of more than 50 people.

He said large gatherings, especially in confined spaces, were situations where the virus might spread easily from one person to another.

The St. Patrick's Day parade was an early casualty. Mayor Lovely Warren said at the news conference that the popular parade, scheduled for Saturday, would be postponed indefinitely.

Mendoza said organizers of sporting events, religious services, public meetings, school conclaves and business gatherings should consider his advice and make their own decision about the propriety of continuing.

"Gatherings are risky," Mendoza said.

Warren said her political fundraising ball, which was expected to draw 900 people Saturday evening at the downtown convention center, was being canceled.

Mendoza also said that Monroe County nursing homes should limit visitors and take steps to screen employees for any signs of illness. He asked hospitals to re-consider the degree of patient access they will allow.

"Although the risk to our community remains low at this time ... we must acknowledge a need to re-examine our practices," Mendoza said.

News of the local case, as well as a nationwide wave of cancellations and grim news about the virus, may have panic buying. Numerous shoppers reported on social media that stores had long lines, with many having run out of paper and cleaning products and some being low on food staples.

© Sarah Taddeo Crowd at Wegmans East Avenue at 5 p.m. Thursday

Mendoza said county officials have seen no signs yet that the virus, which is passed on when an infected person coughs or sneezes or in some cases touches a surface, is spreading through the community.

But, he said, "we are anticipating at some point seeing community transmission."

As of Thursday morning, 50 people were quarantined at home in Monroe County because of concerns they could have been exposed to the coronavirus. Some of them were associates of the man who tested positive, while others were people who themselves have returned from trips overseas.

Among those in quarantine are the mother and son from Greece who traveled to Italy.

The mother said her son's fever broke Wednesday, roughly at the time he was at Rochester General Hospital. She has had no symptoms, she said. The family, whose story first was reported by WHAM-TV (Channel 13), returned from Italy on Feb. 24, and her son developed the sniffles a week or so later. She had concerns, she said, but was told just to monitor him, as he has allergies.

He was sent home from school with a fever on Monday, and she struggled to get clear direction or access for testing from her pediatrician and others until Wednesday.

Thursday evening, the mother posted on Facebook a relieved message: "THANK YOU for all your prayers and concerns! This was a wake up call for sure. WE ARE NEGATIVE. Praise GOD!" A county spokeswoman confirmed the two had tested negative.

Three other tests of Monroe residents also are pending, Mendoza said Thursday morning.

He would reveal few details about the man who tested positive Wednesday. The man was in isolation in his Rochester home for an indefinite period of time.

He said he had developed a runny nose while backpacking in southern Italy, but had his temperature checked twice at the airport in Rome before boarding his flight. He slept little on the direct flight to JFK, and arrived in the United States feeling jet lagged: "Honestly, it felt like a hangover," he said in an interview.

The man described his screening by customs officials at JFK as lax.

The man wore a mask on the plane and during his return to Rochester on a sparsely filled intercity bus, fearing that with a cold his immunity might be compromised: "I didn’t want to get a coronavirus," he said.

Mendoza and UR Medicine physicians said the man appeared to have done everything right once he returned to Rochester on Tuesday.

First, he isolated himself at home. Having no primary-care doctor of his own, he called the county health department on the advice of a doctor friend, he said. And after the county made the arrangements, he appeared at Highland Hospital on South Avenue about 4 p.m. on Tuesday.

"I think everything happened like clockwork," said Dr. Bilal Ahmed, associate medical director at Highland.

Once at Highland, the patient was outfitted with a protective mask outside the hospital and ushered into the private negative-pressure room. Ahmed and two other providers, all volunteers, wore gowns, face shields and respirators to examine the man and collect oral and nasal swabs.

Mendoza said health investigators are still conducting "contact tracing," or tracking down the network of people in Rochester to whom the man or his close associates could have passed the virus. Officials also are working backward to find people who might have been exposed on the plane from Rome and the man's trip from JFK to Rochester.

Health officials have said for some time they expected COVID-19, which causes mild flu-like symptoms or no symptoms in most people who contract it, to appear in the Rochester area.

The man diagnosed Wednesday night is not necessarily the first in Monroe County to contract the virus. He is just the first person whose test came back positive.

Laboratory testing for the virus has rolled out slowly, nationwide and in New York. Testing didn't become more readily available until the last week or so.

© Mike Wren,New York State Department of Health Coronavirus testing at New York State's Wadsworth Lab in Albany.

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"We are entering a very unsettling time," Mendoza said, but it is a time to "combat emotions" and let facts and science take the lead.

Warren urged residents to take the precautions outlined by the area's medical professionals, including stay home from work if they feel ill.

"We need the public’s help," Warren said. 'We are preparing for the worst, but we are praying for the best."

Cases of COVID-19 have been identified in countless other American communities and in 100 nations around the world. The virus likely has been spreading from person to person in some U.S. cities for weeks.

Three other Monroe residents had previously tested negative for the novel coronavirus.

As of mid-day Wednesday, 216 people in New York had tested positive for the coronavirus. Of that number, 121 were in Westchester County, one of the nation's worst hotbeds for the infectious pathogen. No cases had been confirmed farther west than Ulster and Saratoga counties until Wednesday night.

Just over 1,300 people have been diagnosed with COVID-19 in the United States, with 38 of those people dying from the virus.

Medical experts say the virus is a cause for deep concern but not for panic. About 80 percent of people who have confirmed COVID-19 had symptoms that were no worse than a minor case of pneumonia.

"It causes far more mild illness than severe illness. This may ultimately behave like a very bad flu. That’s the context in which we should be thinking about it," Dr. Paul Graman, the hospital epidemiologist at UR Medicine's Strong Memorial Hospital, told a group of physicians at a March 4 talk.

Initial symptoms of infection often are mild aches and pains and a cough. Fever and stomach distress also can occur.

About 20% of those who contract COVID-19 become seriously ill and may require hospitalization. A study in China, where the virus was first observed in December, found that 1% to 2% of patients will die.

Older people, people with suppressed immune systems and people with pre-existing health problems such as heart disease, high blood pressure, diabetes and asthma fare worse than others, that study found.

The first people who tested positive for the virus in the United States, in January, acquired it while living or traveling in Asia. But by late February, public-health officials reported the first person-to-person transmission in the Pacific Northwest.

As federal restrictions were eased and testing became more common, cases began popping up in one state after another. The first New York was reported Feb. 29, the day after the state Department of Health was cleared to conduct its own testing for coronavirus.

Contact watchdog reporter Steve Orr at sorr@democratandchronicle.com or at (585) 258-2386. Follow him on Twitter at @SOrr1. This coverage is only possible with support from our readers. If you don't already have a digital subscription, please sign up today.

This article originally appeared on Rochester Democrat and Chronicle: First coronavirus case confirmed in Monroe County. Here's the latest.