(CNN) The biggest city in the United States is now a search zone for anyone who had close contact with five people recently diagnosed with novel coronavirus .

At least 13 people across metro New York are infected with coronavirus as of Thursday morning, officials have said.

They include the city's first case of community spread -- meaning the source of infection is unknown.

That patient, an attorney in his 50s, is hospitalized at New York-Presbyterian/Columbia University Irving Medical Center.

The man has an underlying respiratory condition that made him more vulnerable to the virus, said Dr. Howard Zucker, commissioner of the New York State Department of Health.

Cuomo said the man's condition was stable and improving.

The attorney has connections across metro New York City. He works at the Lewis and Garbuz law firm in Manhattan, and his family lives in suburban Westchester County.

Officials are testing "a number" of people at the law firm, and none of the tests that have come back are positive, the governor said.

The man's 20-year-old son attends Yeshiva University in Manhattan, and his 14-year-old daughter attends SAR Academy and High School in the Bronx.

Now, the man's wife, son, daughter and a neighbor who drove him to the hospital are all infected with coronavirus, Gov. Andrew Cuomo said Wednesday.

Only the attorney is hospitalized. His family members and his neighbor are isolated at home, Cuomo said.

SAR High School will be closed through Tuesday, the governor said. Yeshiva University officials said in a statement that classes are canceled through Tuesday. Residence halls and dining facilities will stay open.

"Students who have been quarantined or self-quarantined on campus will be receiving food and will be monitored by our health center along with guidance from city agencies," the university said.

About 1,000 people are being asked to self-quarantine after the latest cases, Cuomo said.

Various health departments will contact those people and provide guidance.

"If anything, we are being over-cautious," Cuomo said.

Those asked to self-quarantine include some congregants of the Young Israel of New Rochelle synagogue in Westchester County.

Young Israel has about 380 family congregants and will be closed through this Sunday, its website says.

How to protect yourself and others from coronavirus • Wash your hands often with soap and water for at least 20 seconds. Be sure to wash the backs of your hands and under your nails. • Avoid touching your eyes, mouth or nose • Stay at least 3 feet (1 meter) away from anyone who may be infected. • If you're feeling sick, cover your mouth and nose when you cough or sneeze. But don't use your hands. Use either your bent elbow or a tissue that you throw away immediately. Sources: US Centers for Disease Control and Prevention, World Health Organization

Anyone who attended Young Israel services on February 22 and anyone who attended a funeral and a bat mitzvah on February 23 must self-quarantine, Westchester County Executive George Latimer said.

Fortunately, Cuomo said, the health care worker knew to stay home after she started feeling sick and has not taken public transportation.

"She took precautions. She basically was isolated at home, went for a test, the test came back positive, and she's isolated in her home again and being treated," Cuomo said Monday.

The woman's husband has also been isolated in their Manhattan home. As of Wednesday, the husband does not have coronavirus, Cuomo said.

But for the five new cases, scouring New York for potential contacts is a daunting task.

The names of the attorney, his family members and his neighbor have not been publicly released. But city health officials are asking anyone who had close contact with the family to call 311.

"Now, more than ever, New Yorkers must come together as a city to limit the spread," said city Health Commissioner Dr. Oxiris Barbot.

"The Health Department will do everything in our power to minimize the disruption caused by this evolving situation, and we will continue to communicate openly and honestly with New Yorkers," Barbot said.

Disease detectives are on Yeshiva's campus in Manhattan trying to identify close contacts of the infected student, New York Mayor Bill de Blasio said. He said two contacts have already been taken to Manhattan's Bellevue Hospital for testing.

While the new coronavirus cases may be alarming, the governor emphasized there's no need to panic.

"We have an epidemic caused by coronavirus, but we have a pandemic that is caused by fear," Cuomo said.

While the elderly and people with weakened immune systems are more vulnerable to severe complications, about 80% of the people who contract the virus recover on their own.

"If you understand the facts, there is no reason for undue anxiety," Cuomo said.