WASHINGTON - A U.S. government staffer who visited Mexico City with President Barack Obama this month came down with flu-like symptoms that spread to family members, who have since recovered, the White House said Thursday.

The Centers for Disease Control and Prevention is testing samples from the family members to see if they might have been infected with the H1N1 swine flu virus suspected of killing up to 176 people in Mexico and one in the United States, White House spokesman Robert Gibbs said.

All four individuals experienced only mild symptoms, and all four have recovered, Gibbs said.

Gibbs said the official, part of an advance team working for Energy Secretary Steven Chu, developed a fever while on the trip. It was not clear whether he had contracted the new strain of flu that threatens to become a pandemic, and he has been well too long for a test to show much.

Health authorities in Maryland tested the sick family members. And on April 28th, the individual's wife, son and nephew tested probable for H1N1. They have tested positive, as I said, for Influenza A. The subtype is unidentifiable, Gibbs said.

That is enough to trigger further tests from the CDC as the new flu shows unclear results on standard seasonal flu tests.

The official himself tested negative. likely because so much time had elapsed since the onset of his symptoms, Gibbs said. Chu also did not develop any symptoms, he added.

Gibbs said Obama, who attended a dinner in Mexico City where the officer was present, had not experienced any symptoms and doctors see no need to conduct any tests on the president.