Why does the city suspect the new coronavirus?

The three patients all had recently been to China, the source of the outbreak. And each one had tested negative for influenza and other common illnesses.

Still, the authorities have cautioned that the three may well turn out not to have the new virus. Most of the suspected cases around the country have not in the end been identified as involving the coronavirus.

Health officials are telling New Yorkers not to be overly concerned

Public health officials note that the ordinary flu has proved to be far more dangerous so far. Across the country, the C.D.C. says 68 children have died of the flu this year, and the agency estimates 10,000 adults have died. The coronavirus has not yet caused a single death in the United States, officials said.

Of course, that could change if the coronavirus begins spreading here. In China, there were 17,205 confirmed infections as of Sunday, and 361 people have died. Among laboratory-confirmed cases, the illness has a fatality rate of about 2 percent, although that’s expected to drop as more mild cases are discovered. For comparison: The 2009 H1N1 “swine flu” pandemic had a death rate estimated at .02 percent.

At times, city officials have given different guidance than scientists at the C.D.C. At a news conference, Mayor Bill de Blasio said transmission of the new coronavirus required “substantial contact with someone who already has it,” adding that “you don’t get it” from touching a surface.

The C.D.C., however, has more cautious advice: “It’s currently unclear if a person can get 2019-nCoV by touching a surface or object that has the virus on it and then touching their own mouth, nose or possibly their eyes.”

For now, only the C.D.C. can test for the new coronavirus

Local health departments around the country do not yet have that capability. “Since it’s a new test, there are set protocols in place where the C.D.C. first has to standardize the way it runs the analysis,” Dr. Barbot explained. She said she hoped that within a week or two, New York City would be able to test for the coronavirus.