Amid signs of a potentially large outbreak of COVID-19, Monroe County Executive Adam Bello declared a state of emergency Saturday morning and later announced that all public schools in the county were closed until further notice.

The hasty actions stemmed from discovery of a second local person who has contracted the novel coronavirus. The new patient, a 60-year-old woman, is employed at Greece Arcadia Middle School and went to work at least two days after she first felt symptoms of the infection.

The Greece school district announced Saturday morning it would close all of its schools, furloughing more than 10,000 young people and setting up major issues with home care and food supply. Arcadia Middle School's 750 or so students have not been quarantined but were told to monitor their health closely.

Several other districts then announced plans to close their doors, and at 2:30 p.m. Bello announced all 22 school districts in the county would suspend classes until further notice in hopes of curtailing spread of the virus.

Closure details were expected to be announced Sunday.

Dr. Michael Mendoza, the county public health commissioner, said the new coronavirus case marked a milestone.

"I believe this is our first example of community transmission of the virus," he said. The woman had not traveled to an area with a high rate of infection, leading officials to conclude she picked up the virus locally.

"We're entering a very unsettling time," Mendoza said. "It is a time that will test us."

He said health investigators are tracing the woman's actions at the school and elsewhere and have not yet encountered anyone she contacted who is showing symptoms of COVID-19.

Officials would not specify her job but said she came in contact with many of the school's students each day.

Mendoza urged everyone, but especially students, staff and parents in Greece, to double-down on hand-washing, mouth-covering and social distancing.

It is not yet known where the woman acquired the infectious pathogen, but Mendoza said they suspect it could have been at St. Josaphat Ukrainian Catholic Church, the prominent onion-domed house of worship on Ridge Road in Irondequoit.

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The woman went to services there March 1, Mendoza said. She first felt sick on March 4, a timeline that he said was consistent with her contracting the virus from a fellow parishioner three days earlier. Other than services March 1, the woman did not go to any crowded locations in early March, he said.

Mendoza said health investigators did not know if there are any members at St. Josaphat's who are suffering from respiratory symptoms.

The church's pastor, the Rt. Rev. Philip Weiner, said he knew nothing about the matter until Mendoza called him Saturday morning. He said he did not know the name of the church attendee who had COVID-19.

Weiner said he's noticed no unusual illnesses among the church's members, and added staff had begun extra cleaning at the church more than a week ago at the direction of their bishop, the Most Rev. Paul Chomnycky.

Mendoza said during the news conference Saturday he was impressed with the church's hygiene regimen, and encouraged them to continue it.

Weiner said the church had canceled bingo night earlier this week because of Mendoza's recommendation to avoid large gatherings, and he said parishioners who felt uncomfortable coming to church should feel free to skip services.

But he said he did not intend to cancel Sunday Mass. "Offering prayers and public worship — spiritual medicine — is the best way to overcome this," Weiner said. "Surely we are praying for the person who attended the service here."

Tracing the contacts of that sick person may prove a daunting task. County health investigators need to look for sickness among the students and adults who were near the woman in Greece from early March through March 11, when she entered Unity Hospital — but also look backward for the person who presumptively passed the virus to her in late February or early March, at church or elsewhere.

And once they find that person, they must look among his or her contacts for still more people who might be sick.

The scenario laid out by Mendoza at a packed Saturday morning news conference is not dissimilar from the one in Westchester County where a single man who contracted COVID-19 wound up passing the virus to numerous other people, causing the closure of schools, businesses and places of worship.

Mendoza identified some of the challenges associated with the closing of schools including trying to set up day care, relying on older relatives for day care and the impact on public spaces like libraries.

Whether Bello's declaration of emergency will help with the challenges related to school closings, or help with the arduous task of contact tracing, was not clear Saturday. County officials did not respond to several requests for an explanation of the purpose of the emergency declaration.

The woman who became Monroe County's second COVID-19 victim arrived at the emergency department at Unity Hospital on Wednesday afternoon and was subsequently admitted to the hospital. She was in stable condition in an isolation room, officials said Saturday.

Test results received Friday evening confirmed the patient suffers from COVID-19.

The patient who tested positive was one of eight patients being tested within Rochester Regional Health — one at Rochester General Hospital, one at United Memorial Medical Center in Batavia, two at Newark-Wayne Community Hospital and four at Unity Hospital.

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Mendoza said he thought test results were pending on eight or nine patients in Monroe County.

The first case of COVID-19, made public Wednesday night, was a city man who acquired the infectious virus during a vacation in Italy, where COVID-19 is rampant. The man said he had mild symptoms in Italy and did not feel well as he flew into JFK International Airport and rode a Greyhound bus to Rochester on Tuesday.

He was examined Tuesday afternoon in an isolated room at Highland Hospital, where samples were taken for coronavirus testing. Results came back positive Wednesday night.

As of Friday, the man remained quarantined at home and was feeling better.

Also on Friday evening, Mendoza announced that county officials are trying to identify four people who were on Greyhound bus 252 with the man to determine if other passengers contracted the virus. Seven other bus passengers have been located and placed on voluntary quarantine. None are showing symptoms of infection.

The virus is passed when an infected person sneezes, coughs or exhales forcefully, emitting droplets of respiratory fluid riddled with the virus. These droplets can be inhaled by people who happen to be within 6 feet of the infected person.

The virus also spreads when an infected person gets oral or nasal secretions on his hands and then touches a surface such as a tabletop, stair rail or door knob.