WASHINGTON — A security aide helping with arrangements during President Barack Obama’s recent trip to Mexico became sick with flu-like symptoms and three members of his family later contracted probable swine flu, the White House said Thursday.

The disclosure from press secretary Robert Gibbs comes days after the White House played down risks to the U.S. delegation on the two-day trip that started April 16. Gibbs remained steadfast that the president was never at risk of contracting the flu, which has quickly spread across the globe.

The employee, who was not named by the White House, is an aide to Energy Secretary Steven Chu and helped plan security for part of the administration’s Mexico trip.

The aide arrived in Mexico on April 13, Gibbs said, and became ill on April 16. He developed a fever on April 17, the day Obama left Mexico for the Summit of the Americas in Trinidad and Tobago. The person in question flew back commercially to Dulles on a United flight on April 18; Gibbs had no details yet on whether people on that flight have been notified.

“Obviously we’ll do everything in our power to ensure that what can be done to alert them will be done,” he said.

Ten other people who were on the presidential trip to Mexico saw the White House doctor afterward for symptoms of illness. All were tested and found not to have swine flu, Gibbs said.

The Obama administration appeared to have found out about the security official’s case only by happenstance.

In the course of conversations about preparations for a possible pandemic, a White House doctor asked the acting director of the Centers for Disease Control and Prevention in Atlanta, Dr. Richard Besser, to notify the administration of any Washington-area cases. Besser said that, in fact, there were some probable cases in Maryland and that they involved an employee of the Energy Department.

The man, who is from Anne Arundel County, Md., near Baltimore, visited his brother on April 19 and his nephew became ill. In the next two days, the aide’s wife and son also became ill, Gibbs said.

Gibbs said the three members of the aide’s family are being tested to see if they had the same strain of swine flu that is threatening to become a pandemic. More than 100 cases have been confirmed within the United States.

Gibbs said the aide is listed as a suspected case of the virus. He returned to work on Thursday.

“The original patient tested negative likely because so much time had elapsed since the onset of his own symptoms that they would not show up in the test,” Gibbs said.

“All four individuals experienced only mild symptoms, and all four have recovered,” he said.

The aide worked on Chu’s security detail and went ahead to prepare for the trip. He attended a dinner with Obama on April 16 but Gibbs said the aide never was close enough to Obama to put the president at risk.

Obama has had no symptoms of the virus and doctors see no need to conduct any tests on his health, Gibbs said.

He also said the energy secretary hasn’t experienced any symptoms.

Asked about others involved in the U.S. delegation to Mexico City, Gibbs said no one else has gotten sick.

The White House declined to release the aide’s identity, citing privacy concerns.