Jill Biden, the first lady, tested positive for Covid-19, the White House announced late Monday night, but she is experiencing only mild symptoms and will remain at the family home in Rehoboth Beach, Del., where she and President Biden spent part of the weekend.

Mr. Biden tested negative for the virus after the first lady’s diagnosis, a spokeswoman said. The president returned to the White House on Monday evening.

Officials said Mr. Biden would continue to test on “a regular cadence” throughout the week and would monitor for possible signs of infection.

The first lady’s diagnosis is a reminder that Covid-19 remains a potent virus in the country.

In recent weeks, public health authorities have noted an increase in the number of Covid infections around the country, though the total number remains low and experts do not believe the United States will experience a dangerous wave of illness like those during the height of the pandemic in 2020 and 2021.

Still, scientists have identified new variants of concern, called EG.5 and BA.2.86. EG.5 has become the dominant variant of Covid in the United States and BA.2.86 — while responsible for fewer infections — shows more than the usual amount of mutations from the original coronavirus, a fact that concerns scientists because it could mean it is better at evading vaccines.

The effects of Covid-19 on daily life in America have largely receded, though it remains a danger for the elderly and people with compromised immune systems.

The number of deaths from the virus is the lowest since the pandemic began, and roughly one-tenth of the levels seen in January of this year. Few people wear masks when they are in public and businesses no longer close for fear of the virus’s spreading.

But doctors are still urging people to make sure they get vaccinated. An updated vaccine expected this fall is designed to better protect against some of the newer variants.

For Mr. Biden, his wife’s illness is a throwback to the beginning of his administration, when the virus was raging and the economy was reeling from closures.

Those days are largely in the past. Mr. Biden rarely mentions Covid or the pandemic in speeches anymore. In Labor Day remarks in Pennsylvania on Monday morning, Mr. Biden only made a glancing reference to the economic effects of the virus.

“We’ve recovered all the jobs lost during the pandemic,” he said. “We’ve added millions more.”

Mr. Biden spent Saturday with his wife as the couple traveled to Florida to tour damage from Hurricane Idalia. They spent Sunday at their home in Rehoboth Beach.

If Mr. Biden does test positive in the next several days, it could jeopardize his plans to travel abroad later in the week. He is scheduled to leave on Thursday for a three-day trip to India, where he is supposed to attend a meeting of the Group of 20 leaders from around the world. He is then scheduled to travel to Vietnam for a day before returning to the United States.