Jill Biden is keeping her schedule despite close contact with the president.

Jill Biden, the first lady, tested negative for the coronavirus in Michigan on Thursday morning, as President Biden tested positive in Washington, D.C.

The first lady has been in recent close contact with the president, but is keeping her travel schedule, which includes stops in Michigan and Georgia on Thursday, according to Michael LaRosa, her spokesman. He said she would follow Centers for Disease Control and Prevention guidance concerning mask-wearing and social distancing.

When asked whether Dr. Biden would quarantine when she returns to the White House, Dr. Ashish K. Jha, Mr. Biden’s coronavirus response coordinator, said at a daily briefing on Thursday, “I have to say, I have not engaged on the question of what happens when the first lady returns back.”

The C.D.C. says that people who are up to date with their vaccinations do not need to quarantine after close contact with someone who is infected, as long as the vaccinated person has no symptoms.

But depending on when Dr. Biden was last in contact with the president, it could be several days before she can safely assume she did not catch it from him. The incubation period for an Omicron infection, or the time period between when someone is exposed to the virus and when they develop symptoms, is about three to four days, on average, according to the C.D.C. It may also take several days for the virus to replicate enough to be detectable.

The C.D.C. recommends that people who have been exposed to the virus be tested at least five days after having close contact with an infected person. (Some experts recommend testing sooner — between two and four days after exposure — because of Omicron’s relatively short incubation period.) People who have been exposed should also watch for symptoms and take other precautions, like wearing a well-fitting mask around others for 10 days, according to the agency.

Dr. Biden, like the president, has received a full course of coronavirus vaccinations, including two booster shots.

“I talked to him just a few minutes ago,” she said of Mr. Biden in Detroit, where she was visiting a summer learning program and wearing a mask. “He’s doing fine. He’s feeling good.”