Monroe County officials have been unable to locate four people who got off a Greyhound bus Tuesday with a Rochester man who is infected with the novel coronavirus to determine if they contracted the virus during the trip.

The acknowledgment came Friday, three hours before the county announced a second person had tested positive for the virus, with the origin unexplained.

Seven other bus passengers who disembarked with the group at the downtown station have been located and placed in voluntary quarantine. None are showing symptoms of infection, officials said Friday night.

The man has the first confirmed case of COVID-19 in the western and central New York area. He contracted the virus during a recent trip to Italy.

The man boarded Greyhound #252 In New York City shortly after 12:30 a.m.Tuesday and got off the bus in Rochester about 7:40 a.m.

The Monroe County Department of Public Health is attempting to locate everyone who got off the bus at Rochester. Those passengers may have been in close proximity to the man as they disembarked.

Monroe health investigators used video and Greyhound records to identify seven of those passengers, but the company's records did not reveal the identities of other four bus riders who got off here.

Dr. Michael Mendoza, Monroe County public health commissioner, said other bus passengers who got off the coach at other stops would have to be traced by other health agencies. People are thought to have exited in Binghamton and in Syracuse. The bus ultimately traveled to Buffalo and then Toronto.

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Asked why the county didn't name the bus company and begin its public search for passengers earlier, Mendoza said an erroneous report by WXXI News had led to initial uncertainty about how the man arrived in Rochester. (The WXXI report suggested the man got a ride from the airport, not the bus station as the man had told health officials).

"I guess you have to look at it from our perspective," Mendoza said in an interview Friday. "I don’t want to go with information that could be wrong. It’s a call that I have to make."

Once health officials reviewed surveillance video from the bus terminal later on Thursday, verifying the infected man had indeed been on the bus and had worn a mask and gloves, the officials believed the risk to other passengers was low.

The expectation was they could identify the final four passengers without having to make a public appeal.

By late Friday, however, Mendoza concluded that health investigators would be unable to use video or Greyhound records to identify those four passengers, and decided to make a public appeal for help.

"My intention, my hope (was that we) would have better information today (Friday)," he said, going on to express concern about the alarm it could set off across New York: "This is going to be an issue for my counterparts across the state. We publish 'Greyhound bus 252,' and anyone who is on that bus … is somebody that has to be contacted."

The infected man told a Democrat and Chronicle reporter that he wore a face mask and "didn't have any neighbors in front of me or next to me" on the bus.

Mendoza said the video showed the man was the last to exit, seemingly confirming his story that he also sat at or near the rear of the bus.

Anyone who rode the bus, or who knows someone who was on that bus, is asked to contact the health department at (585) 753-5164, option 1 during business hours or at (585) 753-5905 on nights and weekends.

Greyhound #252 began at Port Authority Bus Station in New York City and terminated in Toronto. After letting off in Rochester, it made 10 stops, including Batavia, Buffalo and Niagara Falls, Ontario.

Keeping a distance of six feet or more from other people can cut down on the risk of an infected person spreading the virus.Health experts have said a mask can help prevent an infected person from spread the virus but only if it is the right type of mask, it is worn properly and without interruption and if the infected person doesn't reach inside the mask and pick up virus-laden saliva or mucus on his hands.

People are encouraged to avoid large gatherings and practice social distancing throughout the United States. Many popular businesses and activities have shut down during the coronavirus pandemic.

Gov. Andrew Cuomo has already put restrictions on gatherings in New York state. The order prohibits groups of 500 or more and limits bars, restaurants and other venues to cut occupancy levels by 50%.

President Trump declared a national emergency due to the virus on Friday afternoon. He decided to ban travelers from the European Union two days earlier.