How does it spread?

Officials have not fully determined where exactly the virus started or how it is transmitted.

Though coronavirus has been reported in countries other than China, it does not appear to be spreading within those countries, according to the World Health Organization.

“At this time, there is no evidence of human-to-human transmission outside China,” Dr. Tedros Adhanom Ghebreyesus, the W.H.O.’s director general, said at a news conference. “That doesn’t mean it won’t happen.”

Finding out how the coronavirus spreads may require help from a disease detective (like those who investigated the measles outbreak in New York last year).

The flu is the bigger threat in New York right now

The mystery surrounding the coronavirus may also overshadow the dangers that New Yorkers face from a more common virus: the flu.

New York State keeps track of flu cases and reports the totals each week. Starting in October, cases start trickling in. They peak around January and February and usually peter out by August.

The 2017-18 flu season was particularly bad in the state. At its peak, there were more than 10,000 flu cases reported each week for five consecutive weeks, starting toward the end of January.

This flu season looks as if it may be worse. More than 57,000 flu cases have been reported across the state, according to the New York State Flu Tracker.