Still, he said, no amount of planning would do much to mitigate an outbreak that prevents the majority of his manufacturing staff from coming to work. A group of 15 employees cannot suddenly do the work of 50.

Most major companies in the United States have said little about how they would respond to an outbreak, except to note their concern for the health and well-being of employees.

A spokeswoman for Amazon said the company was “watching this situation closely” but declined to comment on specific protocols. Representatives for several major banks, retailers and technology companies said they would look to the C.D.C. for guidance.

Other large companies have already put new precautions in place. Facebook is asking employees who host guests at its corporate offices to make sure the visitors have not recently traveled to mainland China. And at an all-hands meeting on Thursday, executives at the commercial real estate firm SquareFoot in New York told employees to take their laptops home on Friday in case they have to work remotely this next week.

It’s unclear whether workers, especially in retail and manufacturing jobs, would continue to be paid if the coronavirus crisis forced stores and factories to close for an extended period.

For some small-business owners, the coronavirus still feels like a distant threat.

“We’re not trying to overreact,” said Michael Stanek, who runs a company near Cleveland that manufactures toner for printers. “We could probably continue to operate with up to maybe 50 percent of employees sick.”

Still, Mr. Stanek said he was considering ramping up production in the coming days so that the company has enough inventory to keep supplying its customers even if its plant shuts down.

And when he gave out paychecks on Thursday, he reminded employees to wash their hands.

Reporting was contributed by Miriam Jordan in Los Angeles; Donald G. McNeil Jr. and David Yaffe-Bellany in New York; Mike Baker in Blaine, Wash.; and Matt Richtel in San Francisco.