Mayor Bill de Blasio and his public-health team have been holding regular briefings on the coronavirus crisis in New York City, ­detailing the extent of its transmission, updating the public on the progression of the disease in infected persons and offering guidelines for avoiding infection.

All good work, but there are signs that the city is less prepared for a mass outbreak than officials suggest. De Blasio and Health Commissioner Oxiris Barbot have stressed that though the coronavirus is certainly contagious, the mechanics of transmission are relatively limited.

“The virus can only transmit when bodily fluid, such as through a sneeze, cough or spit, is transferred from a person who has the virus, directly into another person,” de Blasio stated in a news release. “Disease detectives have determined that the virus does not survive for more than two or three minutes in open air.”

The claim that coronavirus dies quickly upon exposure to the ­atmosphere is striking; it also seems to contradict information elsewhere. The World Health ­Organization says that the novel coronavirus appears to behave similarly to related viruses and “may persist on surfaces for a few hours or up to several days.” A ­recent article in the Journal of Hospital Infection suggests that, depending on the surface material, it can remain infectious for up to nine days.

If coronavirus loses its potency after two or three minutes, then many intensive practices and precautions are unnecessary, such as constant deep cleaning of buses and subways. Closing schools for 24 hours for sterilization after a local infection — as Gov. Andrew Cuomo has announced he would do — would also be unnecessary.

Asked how the Department of Health had concluded that the ­virus dies quickly in the open air, the mayor was unpersuasive. “There are studies, there are academic studies, there are global and national organizations providing the information they have,” he said. “But you know, the old saying, God bless the child who’s got his own or her own … All ­information is valuable, but the information that we’re gleaning from our own direct experience is the most valuable to us.”

When pressed, Barbot acknowledged that the finding is hypothetical. “This is a novel virus that we’re still learning a lot about,” she said. Since the virus’ surface-contamination properties remain in dispute, the city would have been better off not presenting its own findings as fact. That would make its broader instructions less contradictory.

More troubling is the insistence that New York’s hospital system is fully capable of handling a widespread outbreak, which in ­extreme cases can cause total respiratory failure and necessitate ­intubation. De Blasio and Dr. Mitchell Katz, the head of NYC Health + Hospitals, the largest public-health network in the country, have said ­repeatedly that the hospital system has “1,200 beds that can be brought online immediately,” as a reserve stock.

As a public-health emergency, coronavirus is a logistical crisis about capacity. Most people who get infected, perhaps 80 percent, are asymptomatic or suffer only lightly. Of the remainder, a fraction become seriously ill and require the use of a ventilator.

The disease appears to be spreading exponentially, with the total number of new cases outside China increasing by a factor of 10 every 14 to 16 days. Assuming this trend holds, then the 20 or so cases we see in Gotham now could reach 2,000 by mid-April, 200,000 by mid-May and even 2 million by June.

New York City’s entire hospital system has about 26,000 beds. If 10 percent of the city’s population becomes infected, and only 5 percent of those 850,000 people ­become seriously ill, that would still require 42,500 hospital beds — and nursing staff to tend to the patients, along with ventilators and other equipment.

Katz offered an optimistic take on that prospect: “Our hospitals have tents that would allow us to turn a parking lot into an intensive-care unit.” And he reiterated the relatively small share of patients who will require intensive care.

It’s probably true that, even if 2 million New Yorkers are infected by June, and only 5 percent — 100,000 — need to be intubated, that it wouldn’t happen all at once. Still, the image of intensive-care parking lots is less than encouraging for anxious New Yorkers.

Seth Barron is associate editor of City Journal, from which this column was adapted. Twitter: @SethBarronNYC