The public health authorities descended on a hospital, telling some nurses and doctors they would need to be quarantined. They ordered a synagogue to halt all services, and told attendants at a recent bat mitzvah to stay at home for the rest of the week.
Disease detectives were monitoring lawyers at a small midtown law firm for signs of illness, and scrutinizing the risk of contagion at a university.
The discovery of a second case of the new coronavirus in New York on Tuesday — a man of about 50 who lives in Westchester County, just north of New York City — quickly touched off an intense search by health investigators across the region to determine whether he had infected others, and who might have infected him.
The inquiry stretched from a hospital in Bronxville, N.Y., to a synagogue in nearby New Rochelle, to a law firm and a college campus in Manhattan and to Florida, where the man had visited weeks ago.
The effort provided one of the first glimpses in New York of the kind of comprehensive efforts that have been mounted to stem the spread of the coronavirus around the world — epidemiological detective work that was first conducted in China, where the disease seemed to arise.
Now, it is the reality officials across the United States will face as the epidemic spreads, including in Washington State, where the virus has killed several residents of a nursing home.
What these disease detectives find could well be unnerving, as the scope of the illness’s spread becomes clear.
“I think we have to assume this contagion will grow,” George Latimer, the Westchester County executive, said at a news conference on Tuesday.
On Sunday, the authorities announced the first confirmed case of the new coronavirus in New York: a health care worker who had been infected in Iran, where the illness is raging, and began exhibiting symptoms after returning home. But the health care worker had kept herself largely isolated, and the authorities expressed confidence they had the situation under control.
But the case announced on Tuesday was far more worrisome.
The authorities have little inkling of how the man, a lawyer who lives in New Rochelle but works in Manhattan, had been infected. He had traveled to Miami in February and regularly visited Israel, but had not been to any areas with widespread transmission.
Public health authorities were only beginning to tally the number of people he might have exposed to the illness.
The man became ill on Feb. 22 and was admitted to a hospital in Westchester on Feb. 27., according to Dr. Demetre C. Daskalakis, the deputy commissioner for disease control at New York City’s Department of Health.
The original diagnosis was pneumonia, according to a person who knows the patient well and who spoke on the condition of anonymity. After testing negative for the flu, he was removed from isolation, the person said. Several people visited him.
But his health deteriorated, and after several days he was transferred to NewYork-Presbyterian Hospital in Manhattan. “At that point, it was a bit of a medical mystery,” the person said.
He was tested for the new coronavirus on Monday and health authorities announced the result Tuesday morning. Officials did not specify why the man had not been tested for the virus earlier. He was in “severe condition” as of Tuesday afternoon, according to the Health Department.
Officials acknowledged that doctors, nurses and others at the first hospital the man checked into, NewYork-Presbyterian Lawrence Hospital in Bronxville, might have been exposed to the illness.
“We believe that a couple of the medical professionals have been quarantined,” Mr. Latimer, the county executive, said.
Westchester County health officials were scrambling to trace his movements in the days before his hospital admission. The Westchester health commissioner ordered the synagogue, Young Israel of New Rochelle, to halt all services, and ordered the congregants who attended a bat mitzvah and a funeral there to self-quarantine.
In New York City, investigators with the health department interviewed colleagues at the man’s law firm on East 42nd Street, and identified seven people there worthy of some level of monitoring to see if symptoms develop.
The man has four children, two of whom flew back from Israel in recent days. But the younger two have links to New York City. One child, a daughter, attends a Jewish high school in the Riverdale neighborhood in the Bronx, and the school, SAR, which stands for Salanter Akiba Riverdale and describes itself as a Modern Orthodox Jewish day school, closed on Tuesday as a precaution.
The other, a college student, attends Yeshiva University but had not been on campus since Feb. 27, according to a statement released by the school. City officials said the man’s son, the Yeshiva University student, exhibited light symptoms that could be the coronavirus, or perhaps nothing at all.
Additionally, the school’s statement said, a law school student was in self-quarantine after having contact with the law firm where the Westchester man works.
The man’s family is currently in quarantine in New Rochelle, the authorities said.
The man, now hospitalized, had been planning to attend this week’s annual conference of the American Israel Public Affairs Committee in Washington, D.C., which is typically attended by thousands of people, including members of Congress, according to the person who knows him well.
Gov. Andrew M. Cuomo said news of the second New York patient should not cause alarm, and steeled New Yorkers for the prospect that the virus would spread.
“Yes, people are going to get infected,” the governor said in an interview on Long Island News Radio, adding that most cases involved only mild symptoms. More severe symptoms include pneumonia and respiratory failure. Early estimates put the death rate at 2 percent, although that may drop.
Epidemiologists say it is unsurprising that the illness appears to have spread with little detection given how few people have been tested for the virus. In New York City, fewer than 20 people have been tested; across the state, only a few dozen people have.
Testing on a larger scale has been hampered by regulatory hurdles and limitations that the Centers for Disease Control and Prevention has imposed, although those obstacles are easing.
The city’s public health laboratory discovered that the man had the new coronavirus on the very first day the laboratory began testing, Mayor Bill de Blasio’s office said.
More than 100 people in the United States have been confirmed through laboratory testing to have the new coronavirus.
The new virus is believed to have originated in the Chinese city of Wuhan late last year before spreading to some 70 other countries. More than 92,000 people have been infected, and more than 3,100 have died. New hubs of transmission have emerged in Italy, South Korea and Iran.
The details known about the man’s time at the Bronxville hospital underscore an alarming threat — one undiagnosed patient with the new coronavirus can expose a large number of staff, leading to quarantines.
Elsewhere, hospitals have already been a source of transmission for the new coronavirus. In Wuhan, more than 1,500 medical workers contracted the virus, according to statistics the Chinese government released in mid February. An earlier outbreak of a different coronavirus, the far more deadly SARS, was also fueled by transmissions that occurred in health care settings.
The virus’s impending arrival has caused New Yorkers to grow concerned in the past week. After reports of price gouging on supplies including face masks and hand sanitizers, State Senator Brad Hoylman, a Democrat, introduced a bill on Tuesday to penalize businesses that raised prices on medical supplies by more than 10 percent during a public health emergency.
Concern is sure to grow as health detectives begin to investigate cases around the city. On Tuesday, police officers showed up at the building in Midtown where the Westchester man worked, reportedly after someone in the building called 911 saying they had contact with the man.
Jonathan Crespy had come downstairs to meet his wife for coffee when he learned that a man who worked in the same building as him was the second coronavirus patient. Mr. Crespy had worked from home on Monday out of caution, he said, after learning about the city’s first coronavirus case.
“I came back today,” he said. Asked by a reporter if he would consider working from home again tomorrow, he said, “I think I’ll go home now.”
Joseph Goldstein reported from New York, and Jesse McKinley from Albany, N.Y. Luis Ferré-Sadurní, Michael Gold, Jeffery C. Mays, Annie Correal and Corey Kilgannon contributed reporting.